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Chapter 19
The Deinococci and Nonproteobacteria Gram Negatives
Domain
Phylum
Class
Order
Family
Genus
Species
Domain Bacteria
- volumes 1 and 5 of Bergey’s manual of systematic bacteriology
- Deinococci and nonproteobacteria gram negatives
*gram-negative bacteria not belonging to phylum Proteobacterium
- characteristics include
* morphology, reproduction, physiology, metabolism, and ecology
Figure 19.1
Aquificae and Thermotogae Aquificae
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
- Bacterial thermophiles
* optimum growth temperatures above 85°C
Genus Aquifex
- gram-negative rod
- thermophile
**growth optimum 85°C - maximum 95°C
- microaerophilic
- chemolithoautotroph
*uses hydrogen, thiosulfite, and sulfur as electron donor
*uses oxygen as electron acceptor
* genome ~1/3 size of E. coli
Phylum Thermotogae
- second deepest branch of Bacteria
- contains one class, one order, and six genera
* best studied genus is Thermotoga
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
( e.g., marine hydrothermal vents and terrestrial solfataric springs )
Thermotoga…
- chemoheterotrophs
* have functional glycolytic pathway
* can grow anaerobically on carbohydrates and proteins digests
* ~24% of coding sequences are similar to archaeal genes
( may be due to horizontal gene transfer)
Figure 19.2
Deinococcus-Thermus
- contains one class, Deinococci
- two orders, Deinococcales and Thermales
- three genera
# genus Deinococcus is best studied
* 9 of 11 species are mesophilic
* 2 are thermophilic
Deinococcus-Thermus - 2
- 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
* plasma membrane has large amounts of palmitoleic acid rather than
phosphatidylglycerol phospholipids
Figure 19.3
Deinococcus-Thermus - 3
- aerobic
* catalase positive
- produce acids from only a few sugars
- 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
Deinococcus-Thermus - 4
- 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
* efficient proteins (protected by manganese) and enzymes for DNA repair
- within 12–24 hours can repair chromosomes fragmented by exposure to radiation
Heterocyte
- 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
Phylum Chlamydiae
- gram negative
- obligate intracellular parasites
* must grow and reproduce inside host cells
*although known for ability to cause disease, many grow within hosts such as protists, and
animal cells without adverse effects
- one class, one order, four families, six genera
* genus Chlamydia is best studied
Genus Chlamydia
- nonmotile, coccoid, gram negative
*cell walls lack muramic acid, peptidoglycan
* have very small genomes
- obligate intracellular parasites with unique developmental cycle
*elementary body (EB) attaches to host cell
*reticulate body (RB) reproduction by binary fission
* differentiate back into EB, lyses cell
Figure 19.12
Chlamydial Metabolism
- cannot catabolize carbohydrates
- cannot synthesize ATP or NAD+
* import up from host
*do have genes for substrate-level phosphorylation, electron transport, and oxidative
phosphorylation
- RBs have biosynthetic capabilities when supplied precursors from host; can synthesize some
amino acids
- EBs seem to be dormant forms
Phylum Spirochaetes
- contains one class; one order, three families, 13 genera
- gram negative, chemoheterotrophic bacteria with distinctive structure and motility
* slender, long with flexible helical shape
*creeping (crawling) motility due to a structure called an axial filament
- oxygen requirements vary
Table 19.3
Figure 19.13
Spirochaetes Motility
- axial filament lies inside outer sheath
* rotate, causing corkscrew-shaped outer sheath to rotate and move cell through
surrounding liquid
- motility adapted to moving through viscous solutions
Figure 19.14
Figure 19.15
Symbiotic Associations between Spirochetes and Other Organisms
- ecologically diverse
free living
symbiotic
* hindguts of termites
*digestive tracts of mollusks and mammals
*oral cavities of animals
disease
*Lyme disease and syphilis are spirochete diseases
Phylum Bacteroidetes
- very diverse
- contains three classes
Bacteroides
Flavobacteria
Sphingobacteria
- 12 families, and 63 genera
Class Bacteroides
- anaerobic, gram-negative rods, various shapes
*do not form endospores
*motile or nonmotile
- chemoheterotrophs - fermentative
- often found in oral cavity and intestinal tract of humans and other animals and the rumen of
ruminants
*often benefit host by degrading complex carbohydrates, providing extra nutrition to host
*constitute up to 30% of bacteria from human feces
* some cause disease