Download Prescott`s Microbiology, 9th Edition 42 Biotechnology and Industrial

Prescott’s Microbiology, 9th Edition
42
Biotechnology and Industrial Microbiology
CHAPTER OVERVIEW
Industrial microbiology exploits the range of genetic resources and natural products generated by
microorganisms to produce compounds with industrial or medical application. Genetically engineered
microorganisms can be used to increase the efficiency of the industrial processes and to produce new or
modified products. Major products of industrial microbiology is discussed, including agricultural
biotechnology and microbial energy conversion.
LEARNING OUTCOMES
After reading this chapter you should be able to:
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describe at least five compounds of industrial importance made by microbes
define biocatalysis and explain its advantages over chemical synthesis
compare the value of biofuel use with the challenges presented in its manufacture and transport
discuss at least two types of biofuels
explain the use of the term fermenter as it is used in an industrial setting
describe two types of fermenters
list three techniques used to optimize microbial output of industrial products
compare and contrast three directed evolution technologies
describe how metagenomics increases the pool of microbial products available for screening
explain how the natural infection process used by Agrobacterium tumefaciens has been leveraged for the
genetic modification of plants
defend the use of Bt as a pesticide
describe the use of microbes in nanotechnology
explain the utility of biosensors
CHAPTER OUTLINE
I.
Major Products of Industrial Microbiology
A. Antibiotics
1. Predominantly produced by actinomycetes in the genus Streptomyces and by filamentous fungi
2. Penicillin—careful adjustment of medium composition is used to slow growth and to stimulate
penicillin production; side chain precursors can be added to stimulate production of particular
penicillin derivatives; harvested product can then be modified chemically to produce a variety
of semisynthetic penicillins
B. Amino acids
1. Amino acids such as lysine and glutamic acid are used as nutritional supplements and as flavor
enhancers
2. Amino acid production is usually increased through the use of regulatory mutants or through
the use of mutants that alter pathway architecture
C. Organic acids
1. These include citric, acetic, lactic, fumaric, and gluconic acids
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
Prescott’s Microbiology, 9th Edition
2.
Citric acid is used in large quantities by the food and beverage industry; produced largely by
Aspergillus niger fermentation in which trace metals are limited to regulate glycolysis and the
TCA cycle, thereby producing excess citric acid
D. Biopolymers—microbially produced polymers
1. Used as stabilizers, agents for dispersing particulates, and as film-forming agents; they also
can be used to maintain texture in ice cream, as blood expanders and absorbents, to make
plastics, and as food thickeners; also used to enhance oil recovery from drilling mud
2. Includes dextrans, polyesters, cellulose, and xantham gum
E. Biosurfactants
1. Biosurfactants are biodegradable agents used for emulsification, increasing detergency,
wetting and phase dispersion, as well as for solubilization
2. The most widely used biosurfactants are glycolipids, which are excellent dispersing agents;
many have antimicrobial properties due to their amphipathic nature (disrupt membranes)
F. Biocatalysts—microbial transformations or biotransformations
1. Microorganisms are used as biocatalysts; bioconversions are frequently used to produce the
appropriate stereoisomer; are very specific, and can be carried out under mild conditions
2. Often used to carry out a minor modification of a biomolecule of commercial use
G. Vaccines
1. Mining the genomic sequence of a pathogen allows reverse vaccinology where a possible
antigen gene is identified in-silico and produced in a nonpathogenic organism
2. MenB (Neisseria meningitis serogroup B) vaccine was created this way and the technique
is currently being applied to other pathogens such as Staphylococcus aureus and B. anthracis
II. Biofuel Production
A. Microbial energy conversion
1. Microbial transformation of organic materials into biofuels, such as ethanol and hydrogen that
can be burned to fuel cars or other machines
2. Ethanol is currently used as a gasoline additive
3. Use of corn as a substrate for ethanol has escalated worldwide food prices
4. Biofuel has several disadvantages
a. Absorbs water
b. Cannot be shipped through existing pipelines
c. Contains far less energy
d. May consume more energy than is actually produced
5. Hydrogen as a biofuel compares favorably to ethanol and other fuels
a. Has about three times more potential energy per unit weight than gas, it has the highest
energy-content fuel available
b. A diverse group of microbes produce hydrogen
c. Can be produced through fermentation
III. Growing Microbes in Industrial Settings
A. Industrial microbiologists use the term “fermentation” primarily to refer to the mass culture of
microorganisms; the term has many other meanings to other microbiologists
B. Small-scale laboratory operations need to be scaled up to industrial-sized operations by maintaining
culture conditions during the transition
C. In stirred fermenters, all steps in growth and harvesting must be carried out aseptically and
computers often are used to monitor microbial biomass, levels of critical metabolic products, pH,
input and exhaust gas composition, and other parameters
D. Continuous feed of a critical nutrient may be necessary to prevent excess utilization, which could lead to
production and accumulation of undesirable metabolic waste products
E. Microbial products often are classified as primary or secondary metabolites
1. Primary metabolites are related to the synthesis of microbial cells in the growth phase; they
include amino acids, nucleotides, fermentation end products, and exoenzymes
2. Secondary metabolites usually accumulate in the period of nutrient limitation or waste product
accumulation that follows active growth; they include antibiotics and mycotoxins
IV. Microorganisms Used in Industrial Microbiology
A. Genetic manipulation of microorganisms
1. Mutagenesis—cultures can be improved by mutagenesis with chemical agents and UV light
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in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.
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Prescott’s Microbiology, 9th Edition
2.
Protoplast fusion—involves removal of cell walls (to create protoplasts), mixing two different
solutions of protoplasts, and growth in selective media to prompt recombination to make
useful industrial strains
3. Genetic transfer between different organisms—functional genes are cloned and inserted into
new hosts where heterologous gene expression enables the production of specific proteins and
products
4. Modification of gene expression—modification of regulatory molecules or endogenous
promoters on DNA can increase gene expression
5. Directed evolution
a. Construction of production strains by specifically targeting genes of interest for
mutagenesis
b. Site-directed mutagenesis changes nucleotide sequences using a PCR-based approach
that uses methylation patterns to protect mutated gene copies; only a few nucleotides are
changed at a time
c. Combinatorial biosynthesis uses knowledge of pathways to create altered nonprotein
products (e.g., polyketide antibiotics)
d. Systematic evolution of ligands by exponential enrichment (SELEX) creates large
populations of engineered RNA molecules (aptamers) for use in therapies
e. Selecting the best variants is more rapid using high-throughput screening (HTS) methods
often using robotic 96-well plate assays
6. Metagenomics—since most environmental microbes do not grow in the laboratory,
bioprospecting is often done by examining metagenomic libraries to identify new versions of
known genes and new genes through functional screening after expression in common
laboratory microbes
V. Agricultural Biotechnology
A. The Ti plasmid from Agrobacterium tumefaciens is used to introduce genetic constructs into plant
cells; T-DNA within the plasmid transfers genes to plant cells in a process similar to that of
transposons
B. Biopesticides and bioinsecticides—include uses bacteria, viruses, and fungi, and their genes
1. Bacillus thuringiensis—being used to control insects; accomplished by inserting toxinencoding gene into the plant or by production of a wettable powder that can be applied to
agricultural crops; the toxin gene also has been introduced into crop plants
VI. Microbes as Products
A. Nanotechnology
1. Diatom shells have precise structures at the micrometer scale; these can be grown and the
silicon oxides replaced by magnesium oxides
2. Magnetosomes formed by bacteria are minute, perfectly formed magnetic beads with a
membrane envelope that can be used for drug delivery or diagnostic techniques
B. Biosensors
1. Biosensors make use of microorganisms or microbial enzymes that are linked to electrodes in
order to detect specific substances by converting biological reactions to electric currents
2. Biosensors have been or are being developed to measure specific components in beer, to
monitor pollutants, to detect flavor compounds in foods, and to study environmental processes
such as changes in biofilm concentration gradients; they also are being used to detect glucose
and other metabolites in medical situations and to combat bioterrorism
3. New immunochemical-based biosensors are being developed; these are used to detect
pathogens, herbicides, toxins, proteins, and DNA
CRITICAL THINKING
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© 2014 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution
in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.
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Prescott’s Microbiology, 9th Edition
1.
Discuss how regulatory mutants are used (and why they are necessary) in the production of amino acids.
Cite a specific example and describe the nature of the regulatory changes. Why is it desirable to increase
membrane permeability in these organisms as well?
2.
Genetically engineered microorganisms have been developed for use as pesticides. What steps should be
taken to test the safety of these organisms before releasing them for use in a natural environment? Justify
your choices. If you do not think they should ever be used, state your reasons.
3.
Search the cabinets and shelves in your home and identify products containing compounds made by
microorganisms. List the product, the microbial contribution, and describe the function of the compound
in the product.
4.
Ethanol in the United States is prepared largely from corn sugar fermentation and subsequent distillation.
It is added to many of the gasoline blends to boost octane. Using corn ethanol as a biofuel has received
some criticism from economists who believe it drives the cost of food up and does not yield as much
energy as corn requires external fertilization. There is much interest in utilizing non-foodstuff sources of
cellulose such as switchgrass (Panicum virgatum) to yield sugar for fermentation, but the conversion of
cellulose to sugar is currently a chemical process that does not scale up readily. Comment on how an
industrial microbiological approach might be applied to this problem.
CONCEPT MAPPING CHALLENGE
Provide your own linking words to construct a concept map using the following words:
Ethanol Methane Microbial fuel cell Directed evolution Aptamers Fermentation Antibiotics
Bioprospecting Amino acids Hydrogen Primary metabolite Production strain Biofuels
Anaerobic digester Secondary metabolite
Organic acids
Site directed mutagenesis Combinatorial
biosynthesis Natural product
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© 2014 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution
in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.
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