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Chapter 21
Bacteria: The Deinococci
and Nonproteobacteria
Gram Negatives
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Life on Earth evolved along three major lines, called domains, all derived
from a common ancestor. Each domain contains several phyla. The domains,
Bacteria and Archaea, remained prokaryotic, whereas the third, Eukarya,
evolved into the modern eukaryotic cell.
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Aquificae and Thermotogae
• Thermophiles that
grow at temperatures
above 85° C -Aquificae
and Thermotogae
Figure 21.1
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Phylum Aquificae
• Thought to be deepest (oldest)
branch of Bacteria
• Contains one class, one order, and
five genera
– two best studied genera are Aquifex
and Hydrogenobacter
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Genus Aquifex
• Thermophile with a growth optimum of
85°C and a maximum of 95°C
• Microaerophilic
• Chemolithoautotroph
-uses hydrogen, thiosulfite, and sulfur as electron
donor
-uses oxygen as electron acceptor
-genome ~1/3 size of E. coli
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Phylum Thermotogae
• Second deepest branch of Bacteria
• Contains one class, one order, and
six genera
– best studied genus is Thermotoga
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Genus Thermotoga
• Gram-negative rods
– have outer sheathlike envelope that can
balloon out from ends of cell
• Thermophiles
– optimum 80°C; maximum 90°C
– grow in active geothermal areas
– terrestrial solfataric springs
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Thermotoga…
• Chemoheterotrophs
– have functional glycolytic pathway
– can grow anaerobically on
carbohydrates and proteins digests
• e.g., Thermatoga maritima
– ~24% of coding sequences are similar
to archaeal genes
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Figure 21.2
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Deinococcus-Thermus
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Genus Deinococcus
• Deinococcus is best studied
• Spherical or rod-shaped
– associated in pairs or tetrads
– stain gram-positive but do not have typical
gram-positive cell wall
• layered outer membrane similar to gram-negatives
• L-ornithine in peptidoglycan
• lacks teichoic acid
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Figure 21.3
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Deinococcus…
• Mesophilic
• Mesophilc, aerobic, produce acid
• Extraordinarily resistant to desiccation
and radiation
– can survive 3-5 million rad (100 rad lethal to
humans)
• Isolated from ground meat, feces, air,
fresh water, and other sources, but
natural habitat unknown
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Deinococcus……
• Genome consists of two circular
chromosomes, a megaplasmid, and a
small plasmid
– radiation resistance due to ability to repair
genome when it is severely damaged
• Rapidly repairs fragmented DNA within
12-24 hours when exposed to radiation
• D. radiodurans shown to have an efficient
DNA repair system
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Photosynthetic Bacteria
• Three groups of photosynthetic bacteria
– the purple bacteria
– the green bacteria
– the cyanobacteria
• differ from the purple and green bacteria by
carrying out oxygenic photosynthesis
– have two photosystems
– use water as an electron donor and generate oxygen
during photosynthesis
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Purple sulfur bacteria
Alga
Bloom of Purple Sulfur Bacteria, Sulfide Spring,
Madison, WI
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differences in
absorption
spectra correlates
with ecological
distribution
Figure 21.4
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Taxonomy of Photosynthetic
Bacteria
•
•
•
•
Phylum Chloroflexi – green nonsulfur bacteria
Phylum Chlorobi – green sulfur bacteria
Phylum Cyanobacteria
Phylum proteobacteria purple bacteria
– purple sulfur bacteria
– purple non-sufur bacteria
• phylum Firmicutes – heliobacteria
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Purple sulfur bacteria: Note
the sulfur granules deposited
inside the cells
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Green sulfur bacteria: Note
the sulfur granules deposited
outside the cells
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Purple bacteria
Chlorosomes from green
bacteria
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Halophilic Purple bacteria
Phylum Chlorobi
• Green sulfur bacteria
• Morphologically diverse
– rods, cocci, or vibrios; single cells, chains, or
clusters
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Chlorobi…
• Have chlorosomes
– ellipsoidal vesicles attached to plasma membrane
– contain accessory photosynthetic pigments
– most efficient light harvesting complexes found in
nature
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Chlorosomes –Green Sulfur & Green Non-sulfur
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Chlorobi…
• Lack flagella; nonmotile
• Some have gas vesicles
– used to adjust depth of cell for adequate light and H2S
• Obligately anaerobic photolithoautotrophs
– use H2S, elemental sulfur and H2 as electron
sources
– elemental sulfur deposited outside cell
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Figure 21.5
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Phylum Chloroflexi
• Green nonsulfur bacteria
• Contains photosynthetic and
nonphotosynthetic members
– e.g., genus Chloroflexus –
photosynthetic
– e.g., genus Herpetosiphon nonphotosynthetic
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Genus Chloroflexus
• Thermophilic
– often isolated form neutral to alkaline hot
springs
– grow in form of orange-reddish mats
• Metabolism
– anoxygenic photosynthesis
• does not use water as electron donor
• photoheterotroph
– can grow aerobically as a chemoheterotroph
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Chloroflexus sp.
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Chloronema sp. on
stratified Michigan Lake
Phylum Cyanobacteria
• Largest, most diverse group of
photosynthetic bacteria
• Most obligate photolithoautotrophs;
some can grow slowly in dark as
chemoheterotrophs
• One current classification system divides
group into 62 species and 24 genera
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Photosynthesis in cyanobacteria
• Resembles that of eucaryotes
– have chlorophyll a
• prochlorophytes have chlorophyll a and b
– have photosystem I and II
– oxygenic photosynthesis
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Photosynthesis in cyanobacteria…
• Use phycobiliproteins as accessory
pigments
• phycobilisomes, which line thylakoid
membranes, contain phycocyanin and
phycoerythrin
• prochlorophytes lack phycobilins
• use Calvin cycle to fix CO2
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Cyanobacterial Thylakoids and
Phycobilisomes
Figure 21.6
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contains
phycobilin
pigments
nitrogen
storage
polymer
Figure
21.7
(a)
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typical
gramnegative
cell
wall
site
of
photosynthesis
Figure 21.7b
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Oxygenic Photosynthetic Bacteria
Figure 21.8
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Heterocysts
• Specialized cells used for nitrogen
fixation
– produced when organism is nitrogen
deprived
– differentiate from individual cells in filament
• involves reorganization of photosynthetic
membranes
– thick heterocyst wall prevents O2 diffusion
into heterocyst which would inactivate
nitrogenase, enzyme responsible for nitrogen
fixation
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Heterocysts and Akinetes
Figure 21.9
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Prochlorophytes
• Cyanobacteria in genera Prochloron,
Prochlorococcus, and Prochlorothrix
– distinguished by presence of chlorophyll a
and b and lack of phycobilins
• are the only procaryotes to possess
chlorophyll b
–makes them candidates as ancestors of
endosymbionts that give rise to chloroplasts
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Prochloron
Figure 21.10
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Ecology of cyanobacteria
• Tolerant of environmental extremes
– thermophilic species can grow at
temperatures up to 75°C
– often are primary colonizers
• Can cause blooms in nutrient-rich ponds and
lakes
– some produce toxins
• Often form symbiotic relationships
– e.g., are phototrophic partner in most lichens
– e.g., symbionts with protozoa and fungi
– e.g., nitrogen-fixing species form associations
with plants
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Figure 21.11
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Phylum Chlamydiae
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Genus Chlamydia
• Gram-negative bacteria
– cell walls lack muramic acid and
peptidoglycan
– have very small genomes
• Obligate intracellular parasites with unique
developmental cycle
– involving formation of elementary body (EB)
and reticulate body (RB) or initial body
– found mostly in mammals and birds
– some recently isolated from spiders, clams,
and freshwater invertebrates
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Figure 21.13b
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Chlamydial metabolism
• Appear to be energy parasites, obtaining
ATP from host
– do have genes for substrate-level
phosphorylation, electron transport, and
oxidative phosphorylation
• Reticulate bodies have biosynthetic
capabilities when supplied precursors
from host; can synthesize some amino
acids
• Elementary bodies seem to be dormant
forms
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Important pathogens
• C. trachomatis
– infects humans and mice
– causes trachoma, nongonococcal urethritis,
and other diseases in humans
• C. psittaci
– infects humans and many other animals
– causes psittacosis in humans
• C. pneumoniae
– common cause of human pneumonia
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Phylum Spirochaetes
• Gram-negative bacteria with distinctive
structure and motility
– slender, long with flexible helical shape
– creeping (crawling) motility due to a
structure called an axial filament
• Chemoheterotrophs
• Ecologically diverse
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Figure 21.14
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axial filament = complex of axial fibrils (periplasmic flagella)
Figure 21.15 (a1) and (a2)
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Figure 21.15 (b)
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Figure 21.15 (c) and (d)
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Spirochete Motility
current thought:
axial fibrils rotate, causing
corkscrew-shaped outer sheath
to rotate and move cell through
surrounding liquid
Figure 21.16
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Symbiotic Associations
• Broad range of organisms
• Found in a variety of locations, for
example
– hindguts of termites
– digestive tracts of mollusks and
mammals
– oral cavities of animals
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Spirochete-Protozoan Associations
Figure 21.17
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