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