Proteobacteria

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

Class Alphaproteobacteria Composed of 6 orders and 18 families

Purple nonsulfur bacteria Use anoxygenic photosynthesis All except Rhodocyclus () are found in the -proteobacteria Considerable variation in morphology

Genus Rickettsia Order Rickettsiales, Family Rickettsiaceae Contains species that cause disease in animals

Genus Rickettsia Can grow in vertebrate erythrocytes, macrophages and vascular endothelial cells Blood-sucking arthropods often serve as vectors

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

Hyphomicrobium life cycle

Caulobacter life cycle Stalk lacks cytoplasmic contents May improve efficiency of nutrient uptake (increased surface area)

Caulobacter life cycle

Family Rhizobiaceae Belongs to the order Rhizobiales Contains 2 important genera: Rhizobium Agrobacterium

Rhizobium Grow within root nodules of legumes as nitrogen-fixing symbionts

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

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

Nitrifying bacteria

Class Betaproteobacteria Composed of 7 orders and 12 families

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

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)

Order Burkholderiales Family Alcaligenaceae contains the genus Bordetella Bordetella pertussis is the cause of whooping cough

Order Hydrogenophilales Contain the colorless sulfur bacteria (are also found in the ) Includes the genus Thiobacillus

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

Class Gammaproteobacteria Constitutes the largest subgroup of proteobacteria Divided into 14 orders and 25 families

Class Gammaproteobacteria

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

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

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

Orders Vibrionales, Enterobacteriales and Pasteurellales Closely related orders that each contain a single family

Order Vibrionales Several are bioluminescent Can be free-living or live symbiotically in the luminous organs of fish

Order Vibrionales Vibrio cholerae and V. parahaemolyticus are human pathogens Other species cause diseases in fish

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

Order Enterobacteriales

Order Enterobacteriales E. coli is the best studied bacterium Many members of this order are pathogens including Salmonella, Shigella, Klebsiella, Yersinia and Erwinia

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

Class Deltaproteobacteria Composed of 7 orders and 18 families

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

Order Bdellovibrionales Composed of one family with 4 genera Members of the genus Bdellovibrio prey on other gram-negative bacteria

Order Myxococcales Aerobic soil bacteria with gliding motility Exhibit a complex life cycle

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