Monera (bacteria) CHAPTER 21 Micro-organisms in Nature MOs can only be seen with microscopes and include bacteria, some fungi, some protists (plankton & slime moulds) Study of MOs is called microbiology MOs can occupy a wide range of habitats both aquatic & terrestrial (deep sea vents and mountain tops) Bacteria are found in salt water, fresh water, dust, air, plants and animals Extreme environments such as hot springs, high salt concs, sewage, swamps, human intestines Some can exist in a human stomach pH2, sulphur springs pH1 They can survive extreme pressures and temperatures Basic structure of bacterial cell Basic structure of a bacterial cell – must be able to draw Basic structure of bacterial cell Bacteria range in size from 0.1 - 10µm (micrometres) Bacteria are surrounded by a cell membrane and outside of that is a cell wall The cell membrane often has infoldings called mesosomes which carry out respiration and aid the cell during cell division The cell wall is composed of sugars and protein It prevents the bacteria from swelling with water and bursting when they are in solutions that are less concentrated Outside the wall there may be another protective layer in the form of a semi-solid capsule OR a more liquid slime layer Basic structure of bacterial cell Bacteria have ONE bacterial chromosome consisting of a circular strand of DNA without any surrounding membrane There are no associated proteins with the chromosome Total number of genes in bacteria is quite small (5,000) Most bacteria have small loops of DNA called plasmids Plasmids contain genes that are responsible for bacterial resistance to antibiotics and are used in genetic engineering Bacterial genomes (genomic material) consists of a chromosome AND one or more plasmids Cytoplasm surrounds the chromosome and contains ribosomes, storage granules (food or waste) but NO mitochondria/chloroplasts Many bacteria are motile having a flagellum or flagella Types of bacteria 1. Bacteria are classified into three groups depending on their shape Round (Coccus/Cocci) Are found in pairs, chains or clusters Examples: pneumonia, sore throat, food poisoning & boils 2. Rod (Bacillus/Bacilli) Examples: tuberculosis (TB), tetanus (lockjaw), botulism 3. Spiral (Spirillum/Spirilla) Examples: syphilis, cholera Reproduction – Binary Fission Bacteria reproduce asexually by a method called binary fission When a bacterial chromosome gets to a certain size the DNA strand replicates itself This means there are now two IDENTICAL strands of DNA The cell elongates with a strand of DNA attached to each end Finally the cell splits into two similar sized cells Bacteria can double every 20 minutes if conditions are optimal Mutations in Bacteria Bacteria reproduce asexually which means their offspring are genetically identical Bacteria can evolve quickly due to the speed at which new mutations can spread within rapidly growing bacteria The short life cycle of bacteria mean that any new variation produced by a mutation can be passed very quickly to a large number of bacteria This is how bacteria evolve resistance to new antibiotics Endospores – how bacteria survive Some bacteria survive harsh and unfavourable conditions by producing endospores Endospores are formed when the bacterial chromosome replicates with one of the new strands becoming enclosed by a tough-walled endospore formed inside the parent cell The parent cell then breaks down and the endospore can remain dormant for a long time Endospores – how bacteria survive When conditions are suitable the endospore absorbs water and the tough wall breaks down The chromosome is replicated and a normal bacteria forms again Normal reproduction by binary fission can now occur Endospores are very difficult to kill They can withstand lack of food, water, high temperatures and most poisons Not even killed by boiling water- they can survive hundreds of years Nutrition –how do bacteria get their food? Nutrition is how an organism gets its food Bacteria get their food in four ways (grouped under autotrophic and heterotrophic ***Autotrophic – means an organism makes its own food*** The source of energy to do this can be from sunlight photosynthesis OR from Chemicals reactions – chemosynthesis Photosynthetic bacteria often have chlorophyll on membranes within the cell (NOT in chloroplasts) Nutrition –how do bacteria get their food? Some photosynthetic bacteria have different pigments than plants and use mostly red light Some do not use water but live on hydrogen sulfide gas – these are called purple sulfur bacteria Chemosynthetic bacteria make their own food using energy from reactions involving ammonia, sulfur compounds and iron compounds Example nitrifying bacteria in the nitrogen cycle Nutrition –how do bacteria get their food? ***Heterotrophic means an organism takes in food made by other organisms*** Most bacteria are heterotrophic and they secrete enzymes into their environment and absorb the digested food They are divided into two groups – saprophytes and parasites ***Saprophytes are organisms that take in food from dead organic matter*** Also called decomposers because they cause the source of their food to decay e.g. soil bacteria Nutrition –how do bacteria get their food? ***Parasites are organisms that take in food from a live host and usually cause harm*** Examples are disease-causing bacteria Factors affecting bacteria growth 1. 2. 3. 4. 5. Factors that slow down a process when in short supply are called limiting factors The following factors affect the growth of bacteria Temperature Oxygen concentration pH External solute concentration Pressure Factors affecting bacteria growth 1. The rate of bacterial reactions are affected by temperature Most bacteria grow well at temperatures between 20-30°C some can tolerate much higher temps without their enzymes being denatured - e.g. deep sea vents Conversely, low temperatures slow bacterial growth e.g. why we use fridges and freezers Aerobic bacteria NEED oxygen for respiration – most are aerobic e.g. streptococcus If oxygen concentrations are low, bacterial growth is slow especially in liquids This is why bioreactors often have oxygen bubbled through Factors affecting bacteria growth 2. Anaerobic bacteria DO NOT require oxygen to respire e.g. Clostridium (causes tetanus/botulism) 3. Facultative anaerobes can respire WITH/WITHOUT oxygen e.g. E.coli found in intestines 4. Obligate Anaerobes can only respire in the ABSENCE of oxygen e.g. Clostridium tetani Bacterial enzymes work at specific pHs If a bacteria is placed in an unsuitable pH its enzymes will be denatured Most bacteria grow in or near neutral pH (pH 7) Factors affecting bacteria growth Some bacteria can tolerate very low (acidic) or very high (basic) pHs. Helicobacter pylori can survive stomach pHs as low as pH 2 and often causes stomach ulcers External solute concentration Bacteria gain/lose water by osmosis If the external solution has a higher solute (salt/sugar) conc than the bacteria, water will move OUT of the bacteria which dehydrates the bacteria preventing their enzymes working e.g. the basis for salting/sugaring foods for preservation Factors affecting bacteria growth If the external solution has a lower solute concentration than the cytoplasm of the bacterial cell, water will enter the bacteria The cell wall of bacteria can normally prevent bacterial cells from bursting Pressure Bacterial growth is generally INHIBITED by high pressure as the bacterial walls cannot withstand it Some bacteria can withstand very high pressures e.g. those found in deep sea vents Bacteria used in biotechnology can withstand high pressures as they are genetically engineered to do so. Economic Importance of Bacteria Benefits Lactobacillus are used to convert milk to cheese and yogurt and other bacteria are used to make silage, vinegar, pickles and antibiotics Genetically modified bacteria are used to make insulin, drugs, enzymes, amino acids, vitamins, food flavourings, alcohols and a growing range of products Economic Importance of Bacteria Disadvantages Bacteria cause human, animal and plant diseases such as TB, whooping cough, septic throats, meningitis, typhoid, cholera, diphtheria, dysentery, food poisoning, mastitis, brucellosis ***Pathogens are microorganisms that cause disease*** Bacteria cause food decay, lactobacillus causes milk to go sour Bacteria in the mouth converts sugar to acid which erodes tooth enamel causing tooth decay Antibiotics ***Antibiotics are chemicals produced by microorganisms that stop the growth of or kill other microorganisms without damaging human tissue*** Antibiotics are used to control bacterial infection Antibiotics DO NOT AFFECT viruses Alexander Fleming isolated the first antibiotic from a fungus in 1928 and by 1940 antibiotics were widely in use to treat bacterial infections Nowadays new antibiotics are produced by genetic engineered bacteria e.g. streptomycin, neomycin and tetracycline Antibiotic Resistance When an antibiotic is used to treat an infection MOST of the bacteria are killed However antibiotic resistant bacteria develop by mutation These are NOT affected by the antibiotic so new antibiotics must be continually produced to combat these If a person is taking antibiotics, all the bacteria are killed If antibiotic resistant bacteria evolve/enter then these bacteria have NO competitors and reproduce very fast and take over If another pathogenic (disease-causing) bacteria enters a persons body, the antibiotic-resistant gene may be passed on to it. Antibiotic Resistance The person will then develop an infection for which the antibiotic is NOT an effective treatment Recently bacterial strains have emerged that are resistant to almost ALL known antibiotics These bacteria are called multi-resistant e.g. MRSA and C.difficile These are becoming widespread, especially in hospitals Overuse of antibiotics (in medicine and agriculture) is leading to the emergence of antibiotic resistant bacteria Failure to complete a course of antibiotics allows the bacteria to survive and grow leading to more antibiotics and risk of resistant bacteria growing HL - Bacterial Growth Curve – you must be able to draw, label and explain each stage Bacteria divide by binary fission Nutrient agar, warm environment Log scale Five phases A, B, C, D, E A. Lag phase During this phase the bacteria adapt to their new environment May make new enzymes to digest nutrients Little if any increase in bacterial numbers HL - Bacterial Growth Curve – you must be able to draw, label and explain each stage B. Log phase Also called exponential phase Bacteria reproducing at maximum rate Numbers doubling in every generation Ideal conditions – nutrients/food, temp, pH, moisture, space etc C. Stationary phase NO INCREASE in bacterial numbers New bacteria compensated by death of same number of bacteria HL - Bacterial Growth Curve – you must be able to draw, label and explain each stage D. E. Rate of growth slows due to lack of food, space, moisture, oxygen, build up of toxin wastes Decline phase Bacteria numbers fall due to the death rate exceeding the rate of reproduction The slow rate of reproduction is caused by the same factors that caused the stationary phase Death or survival phase Not all bacteria die, a small number may survive as spores which remain dormant until conditions become suitable again HL - Food Processing Modern bioprocessing involves using bacteria and other organisms to produce a wide variety of foods and other products Yoghurts, cheeses, artificial sweeteners, amino acids, vitamins, flavourings, enhancers, beer, wine Growing trend of using microorganisms themselves as a food source, especially as protein The use of bacteria (yeasts, fungi and algae) to produce edible forms of protein is called single-cell protein (SCP) production There are two main methods of production: batch culture or fermentation and continuous flow culture (fermentation) Batch Culture versus Continuous Flow Batch Culture Continuous Flow Fixed amount of sterile nutrient added to the MOs in the reactor Nutrients are added continuously to the reactor The MOs go through the lag, log & stationary phase – nutrients used up, product formed Some of the microorganisms are withdraw so that the volume of material in reactor stays constant Products normally formed during log or stationary phase MOs maintained more or less constantly in the log stage of growth Nutrients used up and product is formed Growth is rapid & product is produced at a fast rate Process is stopped before the decline phase due to lack of product being formed, risk of unwanted side products being formed Temp, pH, stirring rate, nutrient conc, oxygen all kept constant At the end of the run, the bioreactor is emptied, product is separated from the solution & purified, reactor is cleaned, process repeated e.g. antibiotics Maintaining these conditions is challenging so only a small number of products made this way e.g. SCP & waste water treatment
