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Proteobacteria
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Proteobacteria Largest and most diverse group of bacteria (450 genera) Sometimes called purple bacteria Purple photosynthetic bacteria found in , , and classes Proposed that proteobacteria arose from a photosynthetic ancestor
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Class Alphaproteobacteria
Composed of 6 orders and 18 families
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Purple nonsulfur bacteria
Use anoxygenic photosynthesis All except Rhodocyclus () are found in the -proteobacteria Considerable variation in morphology
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Genus Rickettsia Order Rickettsiales, Family Rickettsiaceae Contains species that cause disease in animals
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Genus Rickettsia Can grow in vertebrate erythrocytes, macrophages and vascular endothelial cells Blood-sucking arthropods often serve as vectors
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Prostheca bacteria A prostheca is an extension of the cell that is narrower than the cell Two of the best studied examples are the genera Caulobacter and Hyphomicrobium
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Hyphomicrobium life cycle
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Caulobacter life cycle
Stalk lacks cytoplasmic contents May improve efficiency of nutrient uptake (increased surface area)
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Caulobacter life cycle
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Family Rhizobiaceae Belongs to the order Rhizobiales Contains 2 important genera: Rhizobium Agrobacterium
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Rhizobium Grow within root nodules of legumes as nitrogen-fixing symbionts
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Agrobacterium Does not stimulate nodule formation or nitrogen-fixation Invades plant cells and induces the formation of a tumor Ability to induce tumor formation is dependent on a plasmid
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Nitrifying bacteria Located in the alpha, beta and gamma proteobacteria Oxidize either ammonia to nitrite or nitrite to nitrate Play an important role in the ecology of soil
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Nitrifying bacteria
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Class Betaproteobacteria
Composed of 7 orders and 12 families
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Order Neisseriales Composed of a single family (Neisseriaceae) with 14 genera Most studied genus is Neisseria Aerobic diplococci with capsules and fimbriae N. gonorrhoeae and N. meningitidis are human pathogens
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Order Burkholderiales
Contains 4 families Genus Burkholderia in the family Burkholderiaceae Previously grouped with Pseudomonas Burkholderia cepacia is a plant and human pathogen (Cystic fibrosis patients)
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Order Burkholderiales
Family Alcaligenaceae contains the genus Bordetella Bordetella pertussis is the cause of whooping cough
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Order Hydrogenophilales
Contain the colorless sulfur bacteria (are also found in the ) Includes the genus Thiobacillus
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Genus Thiobacillus Grow aerobically by oxidizing various sulfur containing compounds Can tolerate very acidic conditions Production of sulfuric acid by T. ferrooxidans can corrode metal and concrete
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Class Gammaproteobacteria
Constitutes the largest subgroup of proteobacteria Divided into 14 orders and 25 families
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Class Gammaproteobacteria
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Order Chromatiales /Purple sulfur bacteria
Divided into 2 families Are strict anaerobes that oxidize hydrogen sulfate to S0 and deposit it as intracellular sulfur granules
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Order Methylococcales
Use methane, methanol and other reduced one-carbon compounds as both their sole carbon and energy sources Referred to as methylotrophs Contains the genera Methylococcus and Methylomonas
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Order Pseudomonadales
Most important genus in the order is Pseudomonas Many can degrade a wide variety of organic molecules Some are pathogens of animals and plants
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Orders Vibrionales, Enterobacteriales and Pasteurellales
Closely related orders that each contain a single family
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Order Vibrionales Several are bioluminescent Can be free-living or live symbiotically in the luminous organs of fish
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Order Vibrionales Vibrio cholerae and V. parahaemolyticus are human pathogens Other species cause diseases in fish
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Order Enterobacteriales
Composed of one family (Enterobacteriaceae) with over 40 genera Often referred to as enteric bacteria Can be distinguished by their different metabolic properties
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Order Enterobacteriales
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Order Enterobacteriales
E. coli is the best studied bacterium Many members of this order are pathogens including Salmonella, Shigella, Klebsiella, Yersinia and Erwinia
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Order Pasteurellales Composed of a single family with 6 genera Members of the family cause diseases in humans and animals Pasteurella multilocida and P. haemolytica are animal pathogens Haemophilus influenzae is a human pathogen
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Class Deltaproteobacteria
Composed of 7 orders and 18 families
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Orders Desulfovibrionales, Desulfobacterales and Desulfuromonadales
Are all anaerobes that use S0, sulfate and other sulfur containing compounds as electron acceptors during anaerobic respiration Very important for the cycling of sulfur within the ecosystem
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Order Bdellovibrionales
Composed of one family with 4 genera Members of the genus Bdellovibrio prey on other gram-negative bacteria
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Order Myxococcales Aerobic soil bacteria with gliding motility Exhibit a complex life cycle
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Class Epsilonproteobacteria
The smallest class of proteobacteria Composed of one order and three families Two important genera are Campylobacter and Helicobacter Both contain human and animal pathogenic species
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