Industrial Biotechnology- Definitions • • • • Industrial Biotechnology refers to the use of microorganisms or biological substances such as enzymes to perform industrial or manufacturing processes. Industrial microbiology or Microbial biotechnology encompasses the use of microorganisms in the manufacture of food or industrial products. Fermentations and fermentation technology. The term Fermentation is derived from the Latin verb ‘Fervere’, ‘to boil’, describing the appearance of the action of Yeast on extracts of fruits or malted grain, due to production of CO2 caused by anaerobic catabolism. Biochemical definition “ Generation of Energy by catabolism of organic compounds” Industrial definition Chemical changes or decompositions produced in organic substrates through the activity of microorganisms. Any process mediated by or involving microorganisms in which a product of economic value is obtained is called fermentation (Casida, Jr., 1968). Other definitions of fermentation A type of energy-converting metabolism in which the substrate is metabolized without the involvement of an exogenous (external) oxidizing agent. Typically, but not necessarily occurs anaerobically in the absence of oxygen. Products are neither more nor less oxidized than the substrate. A process in which chemical changes are brought about in organic substrates through the activity of microorganisms. Any chemical process mediated by microorganisms , which may be aerobic or anaerobic. Carbohydrates are often essential materials for fermentation but organic acids, amino acids, proteins, fats, sterols, alcohols, esters and organic compounds are also fermentable. An anaerobic cellular process in which organic materials are converted into simpler compounds, and chemical energy (ATP) is produced. Fermentation products • Fermentation products command large industrial markets and are assured of market growth because most can not be produced economically by other chemical processes. • Note: The development of modern industrial fermentations is rooted in traditional fermentations, with applications in the production of fermented foods and beverages such as beers and wines, fermented dairy products (yoghurt and cheese), fermented meats and vegetables. • More recently antibiotics, industrial ethanol, organic acids, vitamins, and enzymes such as amylases, proteases, cellulases and lipases have been produced through fermentation processes. Types of fermentation Traditional • Wine, beer, vinegar, bread, cheese, yoghurt. Industrial (20th century). There are 5 major groups of commercially important fermentations: • Microbial cells or biomass as the product, e.g. single cell protein, baker’s yeast, lactobacillus sp. for starter cultures. • Microbial enzymes; catalase, amylase, protease, pectinase, glucose isomerase, cellulase, hemicellulase, lipase, lactase. • Microbial metabolites: - Primary metabolites; fuel/ industrial ethanol, citric acid, acetic acid, glutamic acid, lysine, vitamins, polysaccharides. - Secondary metabolites- antibiotics eg. penicillin • Recombinant products (genetically engineered) - e.g insulin. • Biotransformations e.g. steroid biotransformation. Advantages of fermentations • Complex molecules such as proteins can not be produced by chemical means. • Bioconversions give higher yields. • Biological systems operate at lower temperatures and near neutral pH. • Can achieve exclusive production of an isomeric compound. Disadvantages of fermentations • Can be easily contaminated with foreign unwanted microorganisms (Minimize by aseptic operation of fermenter). • The desired product will usually be present in a complex product mixture requiring separation. • Slow when compared to chemical processes. Essential features of a fermentation unit • Fermenter. • Culture collection laboratory- provides suitable inocula for initiation of required microbiological processes and makes routine sterility checks on fermentation broths. • Control lab - Monitors each fermentation process with assays for reducing sugars, total hydrolysed sugars, and available ammoniacal nitrogen. Also carries out routine determinations of pH and mycelial weight to provide a biochemical picture of the progress of each batch. Fermentation and extraction yields are determined by chemical and biological analyses of samples taken at various points. Fermentation unit (essential features cont’d) Services • Clean water for fermentation media. • Cooling water for temperature control- treated to remove hardness. • Sterile compressed air for aeration. • Boiler house to supply sufficient high pressure steam for sterilization of ingredients. • Adequate supply of electricity to run stirrer motors and air compressors. • Acceptable system of waste disposal. Fermentation unit (essential features cont’d) • Ingredients store: bulk storage for inflammable solvents, sugars, cornsteep liqour, cornmeal and ionexchange resins. • Investigation laboratory: conducts microbiological and biochemical studies of the fermentation and extraction process to increase the yield and efficiency of extraction. • Extraction area. Fermenter design Fermenters for aerobic respiration • Typically a closed vessel that can be sterilized, aerated, stirred, and have the temperature of its contents regulated with a high degree of accuracy. • The shape is usually cylindrical, with a rounded base and smooth interior to facilitate cleaning. • A stirrer shaft runs through the center of the fermenter. • Has impellers (protrusions from shaft) which are dependent on fermenter height and intensity of agitation required. • A cooling system required to remove heat generated by stirring and metabolic heat generated by microbial cultures. The optimum temperatures for penicillin and streptomycin fermentations are 25oC and 28oC, respectively. • Has a non-return air valve to the sparger at the bottom of the vessel. • A bacteriological filter in the exhaust pipe to the atmosphere minimizes dissemination of microorganisms present in spent air. • Addition of anti-foam prevents loss of broth as foam. Fermenter design - Mixing of substrates • Transfer of energy, substrates, and metabolites must be brought about by a suitable mixing device. The efficiency of the transport of any one substrate may be crucial to the efficiency of fermentation. • Microbial fermentation is a three phase system with liquidsolid, gas-solid, and gas-liquid interfaces. • The liquid phase contains dissolved salts, substrates and metabolites. • The solid phase consists of individual cells, pellets, insoluble substrates or precipitates of metabolic products. • The gaseous phase provides a reservoir for oxygen supply, CO2 removal, or for adjustment of pH with gaseous ammonia. Fermenter design- stirrers • Stirring brings about dispersion of air in nutrient solution, homogenization to equalize temperature and concentration of nutrients throughout the fermenter, suspension of microorganisms and solid nutrients, and dispersion of immiscible liquids. • Gas is distributed through pumps and by stirring. Air enters fermentation liqour by an air-sparger at the bottom of the fermenter, beneath the lowest impeller. • The disc stirrer is the most widely used, where 4-8 radial blades/ impellers project out from the edge of the disc. Blades may be curved in turbine stirrers. • Baffles transfer turbulence to fermenter walls, with four baffles commonly installed in each fermenter. • Foam separators- Foaming is frequently a problem in large scale aerated systems. Anti-foam chemical agents cannot always be added as they may have inhibitory effects on fermentation. Foam can be broken down by mechanical means e.g. rakes mounted on stirrers or by centrifugal force. Construction materials/ anaerobic fermenters Construction materials • Select materials that can withstand repeated steam sterilization. • Stainless steel is mainly used for industrial and pilot scale fermenters. Anaerobic fermenters Fermenters designed for anaerobic fermentations are similar to aerobic fermenters but features for aeration are unnecessary. The intensity of agitation is sufficient only for mixing and maintenance of temperature. Process control Defined environmental conditions for biomass and product formation are critical for the success of fermentations. Temperature, pH, oxygen concentration etc. should be maintained by monitoring and correction through control systems. • Rapid changes in pH are minimized or controlled by choice of carbon and nitrogen source, incorporation of buffers, and addition of appropriate quantities of ammonia, NaOH or acid. • Foam levels are monitored with a stainless steel probe inserted through the top plate of the fermenter. When foam rises and reaches the level of the probe, a current passes through the circuit with foam acting as an electrolyte , and a signal is given off. Temperature control Temperature control • Heat produced by microbial activity and mechanical agitation may be removed from the system by chilled water in external jackets. • Extra heat may be provided by use of internal heating coils or heating jackets. There may be overheating at point source with the use of heating coils but efficiency of heat transfer by use of heating jackets may be limited in large vessels due to the surface area/ volume ratio. Process parameters measured in fermentation processes. Physical Chemical Biological Turbidity Viscosity Temperature Weight of fermenter Pressure Agitator shaft power Foam Flow rate Power consumption pH Redox potential Exit gas analysis (O2, CO2) Dissolved O2 Medium analysis Substrate product concentration. Active product Enzyme activity Protein content. Scale-up Scale-up is the operation of a fermentation process at higher production levels. An efficient process at labscale may perform poorly when attempted on a large scale as the fermentation conditions designed at labscale may not be applicable at industrial scale. It is therefore important to evaluate scaled-up processes for maximal yield, and minimal operating time and cost. Aseptic operation Aseptic operation is the protection of microbial media, cultures, and equipment against contamination and subsequent production of undesired metabolites . This may be achieved through : • Foam control • Sterilization of fermenters, air supply, and nutrient media. • Aseptic addition of inoculum, nutrients and supplements. • Aseptic sampling- Sample tubes are closed by external valves connected to steam lines for sterilization of the valve area between samplings. Sterile transfer between fermenters. • Inoculum or substrate in a small fermenter may be transferred to the main fermentation vessel by air pressure through sterilized transfer lines. Transfer should be as rapid as possible to prevent excessive aeration. Maintenance of sterility in fermentations • Minimum number of openings in fermenter. • Small openings should be made leak- proof with O-rings and larger openings with flat gaskets. • Injection ports should be covered with steam – sterilizable closures • No direct connection between non-sterile and sterile areas. • Sterile pipes should be slanted to collect condensate and to drain it. Batch culture • Batch culture is a closed system. Sterilized nutrient solution in the fermenter is inoculated and fermentation is allowed to proceed without the addition of new nutrient. The composition of the culture medium, biomass concentration and metabolite concentration change constantly as a result of cell metabolism. • The four typical phases of growth in batch culture are lag, log, stationary and the death phase. • Biomass and primary metabolite production occur at the growth (log) phase, and secondary metabolite production occurs during the stationary phase i.e. conditions of substrate limitation. • Batch culture may be used for biomass, primary and secondary metabolite production. • Examples of batch culture fermentations are- antibiotic production, brewing, wine production, and dairy (lactic) fermentations. Advantages of batch culture Advantages of batch culture are: • • • • Production is intermittent and based on quantities that are required. Secondary metabolites are produced during the stationary phase and therefore in batch processes only. Instability of strains requires regular renewal - in batch culture fresh inoculum is used for each production batch. Continuous processes present technical difficulties , are labour intensive, and require constant attention. Batch processes are less costly and are simple to operate. Growth phases in Batch culture Lag phase Phase of cell enlargement and adjustment to culture conditions. Duration varies with culture conditions and with species, but inoculation with young actively growing cells at optimal conditions minimises lag. Exponential (log) phase. • Cell division is most rapid at this phase. • Examples of minimal generation times are 13 -17 minutes for E. coli and 6-18h for M. tuberculosis. Stationary phase • There is a balance between cell division and cell death and the net population is constant. • Growth is limited by exhaustion of nutrient supply and the generation of toxic wastes. • For a species, a more or less uniform maximum population per unit volume is usually attained e.g. max 1010/ml for E. coli. Death phase Decline in cell numbers as rate of cell death exceeds cell division due to accumulation of waste and depletion of nutrients. Fed-batch culture • • • • • • In a fed-batch culture, the initial culture is fed sequentially or continuously with the same medium used to establish the culture, without removal of culture fluid, resulting in an increase in volume. A solution of the limiting substrate at the same concentration as that in the initial medium may be added, resulting in a significant increase in volume. A concentrated solution of the limiting substrate may be added, resulting in a minimal increase in volume. A very concentrated solution of the limiting substrate may be added resulting in an insignificant increase in volume. In fed-batch culture, the concentration of the limiting substrate can be maintained at a low level, avoiding repressive effects of high substrate concentration. Fed batch culture is used in the production of bakers’ yeast as an excess of malt leads to a high growth rate that results in oxygen depletion. Also used in penicillin production in the slow growth phase (production phase) by a controlled glucose feed Continuous culture • Microbial populations can be maintained in a state of exponential growth by continuous culture, which is an open system where fresh medium is continuously supplied from a reservoir, and an equal amount (excess medium) is removed continuously from the system through a siphon. • Ensure dilution rate is equal to the growth rate so that the cell loss as a result of outflow is balanced by growth so that there is no change in bacterial mass (concentration) and the system is in a steady state. If the dilution rate exceeds the growth rate, there is progressive dilution of culture, resulting in a washout or loss of culture. Advantages/ disadvantages of continuous culture • Continuous fermentation processes have been developed for the production of single cell protein, starter cultures, organic solvents and ethanol. • The advantages of continuous fermentation processes are potential high yields of biomass and primary metabolites as growth rates are maintained at optimal levels in the log phase and production is continuous, ensuring high production volumes. • Disadvantages are the complexity of the system, high cost, inflexible production schedule and the difficulty in maintaining sterile conditions over a long period of time. Mutant strains may also arise and overgrow production strains. Continuous culture in chemostats/turbidostats Chemostats • The chemostat consists of a culture vessel and a reservoir that supplies nutrient medium at a constant rate. • Growth is controlled and maintained by monitoring the pH or carbon dioxide concentration of the medium or by monitoring the concentration of the limiting nutrient . Turbidostats • In turbidostats continuous culture is based on keeping the turbidity and bacterial concentration constant. • Nutrient flow is controlled by a turbidity probe switch mechanism. Calculation of media flow rate The dilution rate (D) = F/ V Where: D is the volume change/ hour. F = flow rate of medium into the fermenter, given as litres per hour. V = volume of culture medium in litres and specific growth rate is the number of generations per hour. N.B. If the dilution rate exceeds growth rate, the culture becomes progressively diluted to extinction and is said to have undergone a washout. Example 1. If the flow rate F is 30 ml/hr and V is 100 ml, the dilution rate is (30/100)/h = 0.3/ h. 2. A vessel of 1000mL has a flow rate though it of 500ml/hr. The dilution rate is 500/1000 = 0.5/h. Problem 1 • If the specific growth rate of a culture in a continuous fermentation is 0.8 generations per hour and the vessel has a capacity of 500 L what is the maximum flow rate if culture washout is to be avoided? Industrial microrganisms : Selection criteria Selection of the culture to be used is a compromise between productivity of the organism and the economic constraints of the process. Criteria include i. Nutritional characteristics of the organism (The process must be carried out using a low cost medium). ii. The optimum temperature of the organism. iii. Reaction of the organism with the equipment to be employed. iv. Stability of the organism and its amenability to genetic manipulation. v. Productivity and yield per unit time. vi. Ease of product recovery from culture. vii. Toxicity of the organism and product. Isolation of Industrial microorganisms • The first stage in screening for microorganisms of potential industrial application is their isolation, which involves obtaining either pure or mixed cultures, followed by their assessment for ability to carry out the desired reaction or produce the required product. • Ideal isolation procedures start with an environmental source, frequently soil, which is likely to be rich in the desired microorganisms, and are designed to favour the growth of those organisms possessing the industrially important characteristic. • The desired characteristic is used as a selective factor and a simple test is applied to distinguish the most desirable types. Selective pressure may be used in the isolation of organisms which will grow on particular substrates or under conditions that are adverse to other types. • Alternatively, select for a target species or taxon known to have the desirable characteristic e.g. Antibiotic production by Streptomycetes. Preservation of industrial cultures • As isolation is lengthy and expensive, it is essential that the organism retains the desirable characteristics that led to its selection, and should be free from contamination. • Cultures should therefore be stored in a way which eliminates genetic change, protects against contamination and retains viability. Storage on agar slopes • May be stored refrigerated at 5oC or frozen at -20oC and subcultured at weekly or six-monthly intervals. Note: Subculturing may result in strain degeneration through mutation and contamination. Broth cultures • May be stored as as glycerol/broth stocks at -30oC. Storage in dehydrated form Freeze-drying/ Lyophilisation • Involves the freezing of a culture, followed by drying under vacuum, which results in the sublimation of water from cells. • The culture is grown to the stationary phase and resuspended in a protective medium e.g. Serum , milk or sodium glutamate. • Cell suspensions are transferred to ampoules, frozen, and subjected to a vacuum at slightly raised temperatures until sublimation is complete. • The ampoules are finally sealed, and the freeze-dried culture stored at refrigeration temperatures with minimal loss of viability for up to ten years. • Improvement of industrial cultures • • • • Natural isolates usually produce commercially important products in low concentrations, and as a mixture with closely related compounds. Consequently, attempts are made to increase the productivity of the selected organism through induced mutations and genetic recombination (e.g. penicillin yield increased from 20 to 8000 units/ml between 1943 and 1955’ and is currently above 85 000 units/ml or 50g/L). Recombinant DNA technology may result in organisms producing compounds which they were not able to produce previously or improve significantly the production of conventional fermentation products. Directed mutation is relevant when genes to be modified are known and a site targeted through in-vitro enzymatic cleavage and manipulation. A knowledge of the biosynthetic route and control mechanism also enables the prediction of a blue-print of the desirable mutant. • Mutagenesis through radiation. • • • • • Non-ionizing (Ultraviolet) radiation. Short wavelength ultraviolet radiation is an effective mutagenic agent at wavelengths between 200 – 300 nm, and an optimum of 254 nm, the absorption maximum of DNA. Long wavelength UV radiation at 300- 400 nm has less lethal and mutagenic effects than short wavelength UV. However, LWUV may be effective if carried out in the presence of DNA intercalating dyes e.g. 8 Methoxypsoralen. Survivors of UV treatment may be twice as productive as parent strains. In mutagenesis through UV irradiation, a strain is exposed to the mutagen, and mutants with required characteristics are selected. Important products of UV action are dimers, (T-T, T-C, C-C), formed between adjacent pyrimidines or complementary strands, which results in cross-links and induces transitions of GC-AT, transversions, frame-shift mutations and deletions. • Ionizing radiation • Ionizing (high- energy) radiation includes X-rays, γ and β rays, and is used when cell material is impenetrable to UV rays. • Single and double strand breaks occur with a significantly higher probability than non-ionizing radiation. • Double-strand breaks result in major structural changes e.g. translocation and inversion and consequently the resultant mutants are often nonviable and do not survive the irradiation process. • Mutagenesis with chemical agents • Mutagenic chemical agents are generally classified into three groups: mutagens which affect non-replicating DNA; base analogs; and frameshift mutagens. Mutagens affecting non-replicating DNA A number of chemicals cause direct damage to non-replicating DNA • Nitrous acid (HNO2) deaminates adenine to hypoxanthine and cytosine to uracil, resulting in AT-GC transitions through the changed pairing properties of the deamination products. • Hydroxylamine (NH2OH) reacts with cytosine, and the derivative from cytosine pairs with adenine, resulting in GC-AT transitions. • Alkylating agents which include N-methyl-N-nitrosoguanidine (a carcinogen), ethyl methanesulfonate, and mustard gas (Di-2clorethyl-sulfide) cause transitions, transversions, and deletions. • Mutagenesis with chemical agents (cont’d) Base analogs Base analogs such as 5- bromouracil and 2- aminopurine are incorporated into replicating DNA instead of the corresponding naturally occuring bases thymine and adenine due to their structural similarity, resulting in AT-GC transitions. • • Frameshift mutagens Frameshift mutagens intercalate into the DNA molecule and cause errors which result in the alterationof the reading frame, resulting in the formation of faulty protein. The most commonly used frameshift mutagens are the acridine dyes such as acridine orange, proflavine and acriflavine. . which are inserted between two neighbouring bases of DNA strands. • Protoplast fusion • Protoplasts (cells devoid of their cell walls) may be prepared by subjecting cells to the action of wall degrading enzymes in isotonic solutions. • Cell fusion, followed by nuclear fusion, may occur between protoplasts of strains that would otherwise not fuse, and the resulting fused protoplast may regenerate a cell wall and grow as a normal cell with characteristics of both parent cells. • Protoplast fusion is used where a sexual reproductive phase is absent in strains, and where conventional techniques have failed. • Example – An asporulating, slow-growing , high antibiotic yield Cephalosporium acremonium strain was crossed with a sporulating fast- growing , low yield strain, resulting in good sporulation, high growth rate and high antibiotic yields. • Application of recombinant DNA techniques • Targeted genetic material derived from one species may be incorporated into another, where it may be expressed. Requirements for transfer and expression of foreign DNA are: i. A vector DNA molecule (plasmid or phage), capable of entering the host cell and replicating within it. ii. A method of splicing foreign genetic information into the vector. iii. A method of introducing the vector and foreign DNA recombinants into the host cell and selecting for their presence. iv. A method of assaying for the required foreign gene product from the population of created recombinants. • Modification of strain properties other than yield • • • • • • • Important characteristics which may be modified include: Strain stability i.e. avoidance of reverse mutants, and maintenance of high yield. Resistance to phage infection. Tolerance to low oxygen tension. Tolerance of high medium components such as high phosphate levels. Low foam production. Favourable morphology for aeration and filtration. Low production of undesirable product (e.g. elimination of the yellow pigment chrysogenein in penicillin producing strains). • Media for industrial fermentations • – Microbial cultures require growth factors e.g. vitamins, specific amino acids and fatty acids which are provided by fermentation media. – Some media components or chemicals added as supplements to media are directly incorporated into the fermentation product and are known as precursors. Corn steep liquor contains phenylethylamine which is incorporated into the penicillin molecule to yield benzylpenicillin (Penicillin G) • • Criteria to be met by media for industrial fermentations • • Media should – Produce the maximum concentration and yield of the product or biomass. – Allow the maximum rate of product formation. – Produce a minimum yield of undesired product. – Be of consistent quality and be readily available throughout the year. – Cause minimal problems during media making, sterilization, aeration, agitation, extraction, purification and waste treatment. • • Defined and undefined media • • Defined media – Pure defined chemicals of known chemical composition may be used for labscale fermentations and some industrial fermentations e.g. production of vaccines for human use. Although composition is controlled, defined media are expensive and not commonly used for industrial fermentations. • Undefined media – Low- cost complex undefined substrates and by-products of other industries are mostly used for industrial scale fermentations. – Cane and beet molasses, cereal grains, starch, glucose, sucrose, and lactose are used as carbon sources. – Urea, corn-steep liqour, soya-bean meal , nitrates and ammonium salts may be used as nitrogen sources. • • • Advantages/ disadvantages of undefined media. • • Advantages – Low cost! • • Disadvantages – Undefined media have a variable concentration of components which may vary with season and among different batches resulting in unpredictable biomass and product yields. – Impurities in natural materials may interfere with fermentations. – Product recovery and effluent treatment may be problematic for undefined media because not all components will be consumed by the organism. Some residual components interfere with recovery and also contribute to the high biological oxygen demand/ organic content of the effluent. • • Medium formulation • – Media should satisfy elemental requirements for cell biomass and metabolic products, and there must be an adequate supply of energy for biosynthesis and cell maintenance. – Identified growth factors e.g. amino acids, vitamins, and nucleotides which can not be synthesized by the culture microorganism should be incorporated into media in adequate amounts. • Role and choice of carbon substrates • – Dual role of carbon substrate – Biosynthesis – Energy generation • • Factors influencing choice of carbon source – The rate at which the carbon source is metabolised as this influences biomass formation and production of primary or secondary metabolites. – Price and availability. – Purity of carbon source. • • Carbon sources: Sucrose/ molasses/ glucose • • Sucrose/ molasses – Sucrose may be supplied in the pure form or as crude sugar molasses with 33.4% sucrose. – Cane or beet molasses are residues left after crystallization of sugar solutions in refining. – Molasses are used in high-volume low-value products e.g. ethanol and singlecell protein and are also used in high-value products e.g. antibiotics. – Use of crude molasses is more cost-competitive in comparison with pure carbohydrates, but impurities will necessitate more expensive and complicated extraction and purification. • Grapes • Grape juice/ must is used as a medium for wine production and contains 17% sugar (glucose, fructose) and 0.3% ash. • • Carbon sources: Starch/ lactose Starch based media • Sources of starch include soya bean meal (35% carbohydrate), groundnut meal, oat flour, rye flour, maize, wheat, sorghum , barley, potatoes and cassava. • Barley • – Raw material for lager beer manufacture. – Has a high carbon content but only 1.5% nitrogen. – Barley is allowed to germinate under controlled conditions for partial digestion of starch by the enzyme amylase in the malting process. – The malted barley is mashed by warming with water and is sterilized by boiling to give wort, the medium to be fermented by yeast to beer. • • Sorghum • Raw material for traditional beer in Southern Africa. • Lactose • Whey powder is used as a lactose source which is slowly metabolized for the production of secondary metabolites. • • Malt extract • Sulfite waste liqours • Carbon sources - Oils and Fats • Vegetable oils e.g. Olive, maize, cotton seed, and soyabean oil may be used as carbon sources, and also for their content of the fatty acids oleic and linoleic acids which are carriers for antifoams in antibiotic processes. • Nitrogen sources • – Most industrial microorganisms can utilize inorganic and organic sources of nitrogen. – Inorganic nitrogen is supplied as ammonia gas, ammonium salts or nitrates. – Ammonia is also used for pH control and is a major nitrogen source in a defined medium for the production of human serum albumin by Saccharomyces cerevisae. – Organic nitrogen sources include urea. – Complex undefined organic nitrogen sources include corn steep liquor, soya meal, and cotton seed meal. • • Factors influencing choice of nitrogen source • – Ammonia or ammonium ion may be used for biomass production. – Antibiotic production is inhibited by a rapidly used source e.g. ammonium, nitrate or amino acids. Production of secondary metabolites begins after depletion of the nitrogen source. • • Best nitrogen sources for some secondary metabolites • Penicillin Corn steep liquor • Bacitracin Peanut granules • Riboflavin Pancreatic digest of gelatine • Novobiocin Distillers’ solubles • Rifomycin Pharmamedia • Gibberelins Ammonium salt • Polyene antibiotics Soybean meal • Nitrogen sources: Corn Steep Liqour • – CSL a by-product of starch and sugar production from maize. – Sugars are extracted from maize by steeping in dilute aqueous sulphur dioxide which establishes an acid pH and prevents putrefaction by controlling the bacterial population. – A well balanced source of carbon, nitrogen, sulphur and mineral salts. Contains lactic acid ,some reducing sugars, and complex polysaccharides. – Phenyl ethylamine which is present in CSL is a precursor in penicillin-G production. • • Corn Steep Liquor cont’d • – The corn sugar extraction process dissolves nitrogen rich substances and minerals, and a natural fermentation by thermophilic Lactobacillus spp. produces lactic acid. – Extracted corn is drained and filtered before the filtrate is concentrated by heat to 50% solids. – CSL contains 4% w/v nitrogen. 25% of the nitrogen is found as alanine, arginine and glutamic acid. Other amino acids include leucine, methionine and cysteine. – Riboflavin, niacin, biotin, and pyridoxine are also significant components, and calcium, phosphorus and potassium are present at 1, 2.5 and 1.5%, respectively. – The acidic nature of corn steep liqour requires inclusion of calcium carbonate (1% w/v) to provide a suitable pH for microbial growth. • • • Nitrogen sources: Soya bean meal / Pharmamedia • • Soya bean meal – Harvested soya bean seeds contain up to 40% protein, 18.5 - 22% oil, 35% carbohydrate, and 5% ash. Ash contains potassium, phosphorus, sulphur, magnesium and iron. – After heating ,flaking , and oil extraction, the residue soya bean meal contains 8% nitrogen in complex form and is used as a nitrogen source in industrial fermentations. • • Pharmamedia – Pharmamedia is a finely ground powder made from the embryo of cotton seed and contains 56% protein, 24% carbohydrate, 5% oil and 5% ash. – Used for the production of tetracycline. • • • Nitrogen sources - Distillers’ solubles • • Distiller’s solubles • The residue after distillation of alcohol from fermented grain contains 6 – 8% solids, and is rich in protein and the vitamin B complex. Suspended solids are removed by screening and the effluent is concentrated to 35% solids to give evaporator syrup and drum-dried to give distillers solubles, which are a rich source of nitrogen and accessory factors. • • • Minerals • – Magnesium, phosphorus, potassium, sulphur, calcium and chlorine are essential elements and may be added at required concentrations as distinct components. – Cobalt, copper, iron, manganese, molybdenum and zinc essential but usually present as impurities in major ingredients. – Inorganic phosphate concentration influences production of bacitracins, citric acid, and oxytetracycline. Monomycins (antibiotics) are produced by Streptomyces at 0.1 mM phosphate levels. • Penicillin G production process • • Penicillin G is produced using submerged processes in 40 000 – 200 000 L fermenters. Larger tanks not used due to resultant inadequate oxidation. • Penicillin fermentation an aerobic process, with an oxygen absorption rate of 0.4 – 0.8 mM/L per min, requiring an aeration rate 0.5 – 1.0 vvm ( Air vol/ liquid vol/ min) • Optimal temperature is 25-27oC. • Inoculum is propagated from lyophilized spores of Penicillium chrysogenum (initially P. notatum) in seed fermenters • To begin the fermentation process, a number of spores are introduced into a small (normally 250-500ml) conical flask of corn steep liquor where it will be incubated for several days. • The culture is then transferred to a 1 or 2 litre benchtop reactor. • Once this has been successful the process is scaledup again to a pilot-scale bioreactor. This reactor will be similar in design to the bench-top reactor except it will have a size of about 100-1000 litres. After about 24-28 hours, the material in the seed tanks is transferred to the primary fermentation tanks. Penicillin production cont’d • A spore concentration of ~ 5x103/ml and pellet formation is crucial for satisfactory subsequent yield. The recommended inoculation rate is 10% v/v. • For optimal penicillin formation rates, pellets must grow in a loose form and not as compact balls. • Growth phase is typically 40- 60 hours in duration, with a generation time of six hours. There is initial rapid proliferation in the growth phase and ammonia is released • Oxygen supply is critical as increasing viscosity hinders oxygen transfer. Penicillin production cont’d • After growth phase, penicillin production phase commences. Growth rate reduced to 0.01 gen/hr. • Production phase may be extended to 120 – 160 hours by feeding with glucose. • Medium for penicillin fermentation by fed-batch culture consists of corn steep liquor of 4-5% dry weight, which may be replaced by Pharmamedia. Additional nitrogen sources such as soy meal or yeast extract, a carbon source (lactose) and buffers are also added to supplement CSL. Corn steep liquor contains phenylacetic acid, a precursor of penicillin G. Penicillin production cont’d • Typical penicillin production medium composition is; lactose 3.5%, glucose 1%, cornsteep liquour solids 3.5%, calcium carbonate buffer 1%, potassium dihydrogen phosphate buffer 0.4%, oils 0.25%, pH 5.5 – 6.0. • Slow glucose feeding (10%) of total volume in the production phase increases yield by up to 25%. The pH is kept constant at 6.5 and phenylacetic acid is fed continuously as a precursor at 0.5 – 0.8% concentration. • Penicillin is excreted into medium, with less than 1% being mycelium bound. • Current yields of ~50g/L are due to culture selection and improvement. Penicillin recovery • Product recovery accomplished by two-stage continuous counter-current extraction of fermenter broth with amyl or butyl acetate. • Broth filtrate mixed with butyl acetate and acidified with phosphoric acid so that the non-ionised penicillin concentrates in the solvent layer. • The butyl acetate phase is then mixed with phosphate buffer at pH 7.0. • Ionized sodium salt of penicillin concentrated in aqueous phase for final isolation. Flow-chart : Penicillin recovery and partial purification 1. 2. 3. 4. 5. Harvest broth from fermenter Chill to 5- 10oC Filter off P. chrysogenum mycelium using rotary vacuum filter. Acidify filtrate to pH 2.0 – 2.5 with sulphuric or phosphoric acid. Extract penicillin from aqueous filtrate into butyl acetate in a centrifugal counter-current extractor . Treat and dispose of aqueous phase. 6. Extract penicillin from butyl acetate into aqueous buffer (pH 7.0) in a centrifugal counter-current extractor. Recover and recycle butyl acetate. 7. Acidify the aqueous fraction to pH 2.0 – 2.5 with sulphuric acid and reextract penicillin into butyl acetate as in 5. 8. Add potassium acetate to the organic extract in a crystallization tank to crystallize the penicillin as the potassium salt. 9. Recover crystals in a filter centrifuge. Recover and re-use butyl acetate. 10. Further processing of penicillin salt. Penicillin G biosynthesis • • • • • • Over 100 biosynthetic penicillins have been produced by adding side-chain precursors, but commercially, only penicillin G and V have been produced. Biosynthesis is inhibited by high phosphate concentration and shows catabolite repression by glucose. In penicillin G biosynthesis the -lactam thiazolidine ring is constructed from L- cysteine and L- valine. Biosynthesis of the penicillin molecule occurs in a non-ribosomal process through a tri-peptide composed of L- cysteine, L-valine and L- aminoadipic acid (AAA). The first product of cyclization is Isopenicillin from which benzylpenicillin is produced by exchange of L --AAA with activated phenylacetic acid. Overall, there is a total of three main and important steps to the biosynthesis of penicillin-G (benzylpenicillin) Penicillin-G biosynthesis cont’d • The first step in the biosynthesis of penicillin G is the condensation of three amino acids L-α-aminoadipic acid, L-cysteine, L-valine into a tripeptide. • Before condensing into a tripeptide, the amino acid Lvaline will undergo epimerization and become Dvaline. After the condensation, the tripeptide is named δ-(L-α-aminoadipyl)-L-cysteine-D-valine, which is also known as ACV. • While this reaction occurs, we must add in a required catalytic enzyme ACVS, which is also known as δ-(Lα-aminoadipyl)-L-cysteine-D-valine synthetase. ACVS is required for the activation of the three amino acids before condensation and the epimerization of L-valine to D-valine. • The second step in the biosynthesis of penicillin G is to use an enzyme to change ACV into isopenicillin N. The enzyme is isopenicillin N synthase. The tripeptide on the ACV will then undergo oxidation, which then allows a ring closure so that a bicyclic ring is formed. Penicillin-G biosynthesis cont’d The last step in the biosynthesis of penicillin G is the exchange of the sidechain group so that isopenicillin N will become penicillin G. Through the catalytic coenzyme isopenicillin – Nacyltransferase (IAT), the alphaaminoadipyl side-chain of isopenicillin N is removed and exchanged for a phenylacetyl side-chain. Penicillin G biosynthesis Citric acid production • 99% of citric acid output is produced microbially and 60% is used in the food and beverage industry as an acidulant and for flavouring fruit juices, ice-cream, candy and marmalade, and as sodium citrate in processed cheese. Some is used in the pharmaceutical industry for iron citrate production and as a blood anti-coagulant. • Mutants of Aspergillus niger are used for commercial production. Strains are also selected for suppression of side products e.g. oxalic acid, isocitric acid and gluconic acid. Production medium • Nutrient medium consists of a 15-25% sugar solution (sucrose or cane molasses purified by cation exchangers or calcium hexacyanoferrate) or potato starch. Each batch of molasses should be given a preliminary fermentation test. • Conversion of carbohydrate to citric acid is dependent on intracellular enzymes. Sugar from nutrient fluid should be able to enter cells of the mycelium, and citric acid produced must be able to diffuse out into the medium. • Copper, manganese, magnesium, iron, zinc and molybdenum are necessary in concentrations optimal for yields. Citric acid- production medium cont’d • pH generally at 5.0 at the beginning of the growth phase, but falls to 3.0 at the production phase due to metabolism of ammonium ions. Low pH reduces incidence of microbial contamination and discourages oxalic acid formation. • 80% of citric acid is produced by submerged processes and 20% by surface processes. Production of inoculum • Spore suspension is used as inoculum after growth for 10 – 14 days in glass bottles on solid substrates at 25oC. • Both numbers and viability of the spore crop are critical. • For submerged fermenters, spores are induced to germinate in a preliminary fermentation. • Nutrient solution containing 15% sugar from molasses is used in the seed fermenter and cyanide ions added to induce pellet formation from mycelial growth. • Spores germinate and form pellets 0.2 – 0.5 mm in diameter within 24 hours at 32oC. • Pellets are then used as inoculum for production fermenters. The efficiency in production fermenters is dependent on the manner off spore and pellet production. Submerged processes • Submerged processes have the advantage of lower total investment by 25%, savings in space requirements, and lower labour costs. • Disadvantages include greater energy costs, and the more sophisticated control technology and highly trained personnel required. • Stainless steel acid resistant fermenters are required to withstand low pH and liners are required for protection in some small- scale fermenters of <1000L. • If the mycelium is loose and filamentous, with limited branches and no chlamydospores, little citric acid is produced in the production phase. Mycelium for optimal production rates consists of small solid pellets. The ratio of iron to copper in a medium determines the mycelial structure. Citric acid submerged processes cont’d • An oxygen concentration of 20 – 25% of the saturation value is required throughout the fermentation. • A foam chamber 1/3 the size of fermenter volume is required. Anti-foam agents e.g. lard oil are added at frequent intervals in the batch fermentation. • The pH reaches 1.5 after 10 days. The maximum titratable acidity attained is directly related to the amount of sugar added to the fermentation medium. • Growth maximum is reached 3-4 days before harvesting. Surface processes employing solid substrates Surface processes employing solid substrates may use either wheat bran or pulp from sweet potato starch production. • pH is reduced to 4-5 before sterilization, after which material is inoculated with spores, spread on trays in layers 3-5 cm thick and incubated at 28oC for 5 days. • Citric acid is extracted from the substrate with hot water. Surface properties using liquid media • Account for up to 20% of the supply of citric acid. • Sucrose is supplied as molasses and inoculation is at 30-40oC by blowing dry spores on the surface or by spraying to 5x 107 spores/m2. • Temperature in the 8-10 cm deep trays is kept constant at 30oC. • Mycelium floats as a white layer on the nutrient solution and yields 1.2-1.5 kg citric acid/m2 after a 14 day fermentation period. • The presence of excessive concentrations of iron results in oxalic acid production and a yellow colouration. Biosynthesis • Citric acid is a primary metabolic product formed in the tricarboxylic acid cycle. • When pyruvate is decarboxylated with the formation of acetyl coenzyme A, acetate residue is channeled to the TCA cycle. • Pyruvate carboxylase is the key enzyme for citric acid production. Citric acid recovery • Citric acid is produced as the calcium salt is precipitated from the fermentation liquor and from washes of the mycelium by treatment between 70 – 90oC at neutral pH for 3-4 hours. • Oxalic acid is precipitated as calcium oxalate at low pH (5.8) leaving citric acid in solution as monocalcium citrate. • Rotating filters or centrifuges are used to separate the mycelium and precipitated calcium oxalate. • At pH 7.2 and 70-90oC, citric acid is precipitated and separated by rotating filters and dried. • Further purification is by adding sulphuric acid to dissolve citric acid and re-precipitating as calcium sulfate. Subsequent recovery steps include treatment (decolourisation) of crude citric acid with activated carbon, and removal of soluble iron with anion exchangers or ferrocyanide and final crystallization. • Above 40oC, crystallization is in the anhydrous form, and below 36oC, in the monohydrate form. • Summary of citric acid recovery process. 1. Filter off A. niger mycelium from harvested broth using a rotary vacuum filter. 2. Add Ca(OH)2 to filtrate until neutral and filter calcium citrate precipitate. 3. Add sulphuric acid at 60oC to calcium citrate to give a calcium sulphate precipitate and release free citric acid. 4. Filter on rotary vacuum filter to recover CaSO4. 5. Decolourise citric acid with activated charcoal. 6. Isolate on cation and anion exchange resins, 7. Evaporate to crystallization at 36oC. 8. Separate crystals of monohydrate citric acid in continuous centrifuges and dry at 50 – 60oC. • Production of streptomycin • Most media for production of streptomycin by Streptomyces griseus provide glucose as the principal source of carbohydrate as the strains are unable to use sucrose. Typical medium is glucose (2.5%), soybean meal (4%), distillers’ solubles (0.5%),sodium chloride (0.25%). • Nitrogen is continuously but slowly available from complex organic sources. • Optimum conditions are: i. Adequate concentration of glucose (~2.5%). ii. Low concentration of inorganic phosphate (≤ 0.006%). iii. Continuous but limited concentration of available nitrogen. iv. Good aeration. v. Temperature 27-29oC. • Three phases in production are: i. Release of ammonia, pH rises from 6.7 – 7.6 in the first 20 hrs. ii. Productive phase – decrease in pH to 6.7. iii. Mycelium disintegrates, pH rises to 8.5. • Industrial ethanol • May be produced by fermentation of any carbohydrate material containing a fermentable sugar (mainly cane or beet molasses). • Yeasts used as fermentation cultures are Saccharomyces cerevisae for hexoses , Candida utilis for lactose and pentoses and Saccharomyces kluyveromyces for lactose. • Ethanol fermentations are also used to reduce the biological/ biochemical oxygen demand (BOD) of industrial effluent.