CHAPTER 30
Industrial Microbiology
Industrial Microorganisms and
Product Formation
Industrial Microorganisms
and Their Products
• Industrial microbiology uses
microorganisms, typically grown on a large
scale, to produce valuable commercial
products or to carry out important chemical
transformations.
• The actual reactions carried out by
microorganisms in industrial microbiology are
called biocatalysis (Figure 30.1).
• An industrial microorganism must produce
the product of interest in high yield; grow
rapidly on inexpensive culture media
available in bulk quantities; be amenable to
genetic manipulation; and, if possible, be
nonpathogenic. There are many industrial
products, including both cells and substances
made by cells.
• Commodity chemicals are inexpensive
chemicals produced in bulk, including
ethanol, citric acid, and many others.
Primary and Secondary
Metabolites
• Primary metabolites are produced during
active cell growth, and secondary
metabolites are produced near the onset of
stationary phase (Figure 30.2).
• Figure 30.3 shows the interrelationship
of the main primary metabolic pathway
for aromatic amino acid synthesis
•and the secondary metabolic
•pathways for a variety of
•antibiotics.
• Many economically valuable microbial
products are secondary metabolites.
Characteristics of Large-Scale
Fermentations
• Large-scale industrial fermentation
presents several engineering problems.
Aerobic processes require mechanisms for
stirring and aeration.
• The microbial process must be continuously
monitored to ensure satisfactory yields of the
desired product.
• Industrial fermentors can be divided into two major classes,
those for anaerobic processes and those for aerobic processes
(Figure 30.4).
• Table 30.1 shows fermentor sizes for various industrial processes.
Fermentation Scale-Up
• Fermentation scale-up is the process of
gradually converting a useful industrial
fermentation from laboratory scale to
production scale. Aeration is a particularly
critical aspect to monitor during scale-up
studies.
Major Industrial Products for
the Health Industry
Antibiotics: Isolation and
Characterization
• The industrial production of antibiotics begins with screening
for antibiotic producers (Figure 30.7).
• Once new producers are identified,
purification (Figure 30.8) and chemical
analyses of the antimicrobial agent are
performed.
• If the new antibiotic is biologically active in
vivo, the industrial microbiologist may
genetically modify the producing strain to
increase yields to levels acceptable for
commercial development.
Industrial Production of
Penicillins and Tetracyclines
• Major antibiotics of clinical significance include the lactam antibiotics penicillin (Figure 30.9) and cephalosporin
and the tetracyclines (Figure 30.11).
• Cephalosporins are valued clinically not
only because of their low toxicity but also
because they are broad-spectrum
antibiotics, useful against a wide variety of
bacterial pathogens.
• Figure 30.10 shows the kinetics of
the penicillin fermentation with
Penicillium chrysogenum.
• If the penicillin fermentation is carried out
without addition of side-chain precursors, the
natural penicillins are produced. The
fermentation can be more directed by adding
to the broth a side-chain precursor so that only
one desired penicillin is produced.
• The product formed under these conditions
is referred to as a biosynthetic penicillin. To
produce the most useful penicillins, those with
activity against gram-negative Bacteria, a
combined fermentation and chemical
approach is used that leads to the production
of semisynthetic penicillins.
• All of these antibiotics are typical secondary
metabolites, and their industrial production is
well worked out despite the fact that the
biochemistry and genetics of their
biosynthesis are only partially understood.
Vitamins and Amino Acids
• Vitamins produced microbially include
vitamin B12 and riboflavin (Figure 30.12).
• The most important amino acids produced
commercially are glutamic acid, aspartic acid,
phenylalanine, and lysine (Figure 30.13).
• Aspartic acid and phenylalanine are the
ingredients of the artificial sweetener
aspartame, a non-nutritive sweetener of diet
soft drinks and other foods sold as low-calorie
or sugar-free products.
• High yields of amino acids are obtained by
modifying regulatory signals that control
synthesis of the particular amino acid such
that overproduction occurs.
• Table 30.3 lists amino acids used in the food industry.
Steroids and the
Biotransformation Process
• Microbial biotransformation employs
microorganisms to biocatalyze a specific step
or steps in an otherwise strictly chemical
synthesis (Figure 30.14).
Enzymes as Industrial Products
• Microorganisms are ideal for the large-scale
production of enzymes. Many enzymes are
used in the laundry industry to remove stains
from clothing, and thermostable and
alkalistable enzymes have many advantages
in these markets.
• Certain enzymes are produced in large
amounts by some organisms, and instead of
being held within the cell, they are excreted
into the medium.
• These extracellular enzymes, called
exoenzymes, can digest insoluble polymers
such as cellulose, protein, and starch. The
products of digestion are then transported into
the cell where they are used as nutrients for
growth.
• The term extremozyme has been coined to
describe enzymes that function at some
environmental extreme, such as high
temperatures or low pH (Figure 30.15).
Enzymes from extremophiles are desirable for
biocatalyses under extreme conditions.
• For some biocatalytic processes, it is
desirable to fix soluble enzymes onto a solid
surface. These are called immobilized
enzymes (Figure 30.16).
• Table 30.4 lists microbial enzymes and their applications.
Major Industrial Products for
the Food and Beverage
Industries
Alcohol and Alcoholic
Beverages
• Alcoholic beverages are produced by yeast
from the fermentation of sugar to ethyl
alcohol and CO2.Wine is produced from grape
juice (Figure 30.18), beer from fermentation
of malted grain (brewing), and distilled
beverages from the distillation of fermented
solutions.
• Commodity alcohol is used as a gasoline
additive and industrial solvent.
Vinegar Production
• The active ingredient in vinegar is acetic
acid, which is produced by acetic acid
bacteria oxidizing an alcohol-containing fruit
juice (Figure 30.22).
• Adequate aeration is the most important
consideration in ensuring a successful vinegar
process.
• Figure 30.23 is a diagram of a vinegar generator.
Citric Acid and Other Organic
Compounds
• A number of organic chemicals are
produced commercially by use of
microorganisms, of which the most important
economically is citric acid, produced by
Aspergillus niger (Figure 30.24).
Yeast as a Food and Food
Supplement
• Yeast cells are grown for use in the baking
and food industries (Table 30.5).
• Commercial yeast is produced in large-scale
aerated fermentors using molasses as the main
carbon and energy source (Figure 30.25).
Mushrooms as a Food Source
• The most important food produced from a
microorganism is the mushroom, which is
produced not for its protein but for its flavor.