Download enteric bacteria

General Microbiology (Micr300)
Lecture 7
Microbial Diversity: Bacteria
(Text Chapter: 12.1-12.3; 12.5-12.11; 12.3;
12.4; 12.17; 12.19-12.25; 12.27)
Phylogenetic Overview of
Bacteria
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Nearly 7000 species of prokaryotes are known.
Figure 12.1 gives a phylogenetic overview of
Bacteria. These bacteria can be divided into at
least 18 Phyla. We will discuss only a number of
common Phyla.
The Proteobacteria consist of five clusters. Each
cluster is designated by a Greek letter: alpha, beta,
gamma, delta, or epsilon (Table 12.1).
Physiologically, Proteobacteria can be phototrophic,
chemolithotrophic, or chemoorganotrophic.
Phylum 1: Proteobacteria
Five clusters:
Alpha, Beta, Gamma, Delta and Epsilon
Purple Phototrophic Bacteria
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Purple bacteria are anoxygenic phototrophs
that obtain carbon from CO2 + H2S (purple
sulfur bacteria) or organic compounds
(purple nonsulfur bacteria).
Purple nonsulfur bacteria are physiologically
diverse, and most can grow as
chemoorganotrophs in darkness. The purple
bacteria reside in the alpha, beta, and gamma
subdivisions of the Proteobacteria.
The Nitrifying Bacteria
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Chemolithotrophs are prokaryotes that
can oxidize inorganic electron donors and
in many cases use CO2 as their sole
carbon source.
Several reactions are involved in the
oxidation of inorganic nitrogen
compounds by chemolithotrophic
nitrifying bacteria (Figure 12.9).
Oxidation of Nitrogen Compounds
Hydrogen-Oxidizing
Bacteria
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A wide variety of bacteria can grow with
H2 as the sole electron donor and O2 as
the electron acceptor; using H2 as their
energy source.
All hydrogen-oxidizing bacteria contain
one or more hydrogenase enzymes that
bind H2 and use it either to produce ATP
or as reducing power for autotrophic
growth.
Methanotrophs and
Methylotrophs
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Methylotrophs are prokaryotes able to grow
on carbon compounds that lack carbon-carbon
bonds. Some methylotrophs are also
methanotrophs, able to grow on CH4.
Two classes of methanotrophs are known, each
having a number of structural and biochemical
properties in common. Methanotrophs reside in
water and soil and can also exist as symbionts
of marine shellfish.
Pseudomonas and the
Pseudomonads
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Pseudomonads include many gramnegative chemoorganotrophic aerobic
rods; many nitrogen-fixing species are
phylogenetically closely related.
Many species use a wide variety of organic
compounds as carbon and energy sources;
some species use over 100 different
compounds.
Pseudomonads are ecologically important in soil
and water – degradation of pollutants.
Free-Living Aerobic
Nitrogen-Fixing Bacteria
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A variety of organisms inhabit soil and are
capable of fixing N2 aerobically.
Azotobacter species are large rods and
obligately aerobic. But their nitrogenases are O2
sensitive. High respiration rate and abundant
capsular slime help protect nitrogenases from
damage of O2.
Resting structures – cysts can form. They are
resistant to dessiccation, UV but not to heat.
Enteric Bacteria
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The enteric bacteria are a large group of
facultative aerobic rods of medical and molecular
biological significance.
Table 12.14 gives the phenotypic characteristics
used to separate the enteric bacteria from other
bacteria of similar morphology and physiology.
One important taxonomic characteristic separating
the various genera of enteric bacteria is the type
and proportion of fermentation products produced
by anaerobic fermentation of glucose.
Rickettsias
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The rickettsias are obligate intracellular
parasites, many of which cause disease.
Rickettsias are deficient in many
metabolic functions and obtain key
metabolites from their hosts.
Spirilla
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Spirilla are spiral-shaped,
chemoorganotrophic prokaryotes
widespread in the aquatic environment.
The genera Helicobacter and
Campylobacter are pathogenic spirilla.
Spirilla are distributed among all five
subdivisions of the Proteobacteria.
Gliding Myxobacteria
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The fruiting myxobacteria are rodshaped, gliding bacteria that aggregate to
form complex masses of cells called
fruiting bodies. Myxobacteria are chemoorganotrophic soil bacteria that live by
consuming dead organic matter or other
bacterial cells.
The life cycle of a typical fruiting
myxobacterium is shown in Figure
12.47.
Phylum 2: Low GC GramPositive Bacteria
Lactic Acid Bacteria
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Lactic acid bacteria and relatives belong
to a group of Gram positve bacteria that
are nonnsporulating and low GC content.
The key genera include Staphylococcus,
Micrococcus, Streptococcus, Lactobacillus
and Sarcina
Bacillus, Clostridium, and
Relatives
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Bacillus, Clostridium, Sporosarcina and
Heliobacterium are major genera that
constitute endospore-forming, low GC,
Gram positive bacteria.
Table 12.25 lists major genera of
endospore-forming bacteria.
One group of endospore-formers, the
heliobacteria, is phototrophic.
Phylum 3: High GC GramPositive Bacteria (Actinobacteria)
The Mycoplasmas
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The mycoplasma group contains
organisms that lack cell walls and contain
a very small genome. Many species
require sterols to strengthen their
membranes, and several are pathogenic
for humans, other animals, and plants.
Major characteristics of mycoplasmas are
shown in Table 12.28.
Coryneform and Propionic Acid
Bacteria
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High GC, gram-positive Bacteria include
such organisms as Corynebacterium,
Arthrobacter, Propionibacterium, and
Mycobacterium. They are mainly harmless
soil saprophytes, with Mycobacterium
species being the exceptions.
The propionic acid bacteria were first
discovered in Swiss cheese, where their
fermentative production of CO2 results in
the characteristic holes.
Mycobacterium
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The genus Mycobacterium consists of
rod-shaped organisms that at some stage
of their growth cycle possess the
distinctive staining property called acidfastness.
This property results from the presence
on the surface of the mycobacterial cell of
unique lipids called mycolic acids, found
only in the genus Mycobacterium
Mycobacterium
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M. tuberculosis is the causative agent of
the disease tuberculosis. M. tuberculosis
cells have a lipid-rich, waxy outer surface
layer that requires special staining
procedures (the acid-fast stain) to
observe the cells microscopically.
Table 12.29 lists some characteristics of
representative mycobacteria.
Filamentous Actinobacteria
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The streptomycetes are a subset of
actinomycetes, a large group of
filamentous, gram-positive Bacteria that
form spores at the end of aerial filaments.
Many clinically useful antibiotics such as
tetracycline and neomycin have come
from Streptomyces species (Table
12.31) – ANTIBIOTIC PRODUCERS.
Phylum 4: Cyanobacteria
and Prochlorophytes
Cyanobacteria
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Cyanobacteria comprise a large and
morphologically heterogeneous group of
phototrophic Bacteria. Cyanobacteria differ in
fundamental ways from purple and green bacteria,
most notably in that they are oxygenic
phototrophs.
Cyanobacteria represent one of the major phyla of
Bacteria and show a distant relationship to grampositive Bacteria.
Oxygen in Earth's atmosphere is thought to have
originated from cyanobacterial photosynthesis.
Phylum 5: Chlamydia
Chlamydia
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Chlamydias are extremely small parasitic
bacteria that cause a variety of human
diseases. Figure 12.85 shows the
infection cycle of chlamydia.
Chlamydias contain a very small genome
and are apparently deficient in many
metabolic functions.