widespread in aquatic and terrestrial environments

▪ aerobic anoxygenic phototrophs, e.g., Roseobacter ▪ nitrogen-fixing bacteria, e.g., Azospirillum ▪ denitrifiers, e.g., Paracoccus ▪ magnetotactic bacteria, e.g., Magnetospirillum

second largest class of Proteobacteria

are typically oligotrophic and strictly aerobic chemoorganotrophs

the largest and most metabolically diverse phylum of Bacteria

has 10 well-characterized orders but vast majority of species fall within the six orders

all gram-negative bacteria

No species have not yet been cultivated in the absence of host cells

typically form prosthecae or stalks and many species display asymmetric forms of cell division

F a c u l t a t i v e i n t r a c e l l u l a r parasites o f animals, zoonotic p a t h o g e n

contain ▪ phototrophs (e.g., Rhodopseudomonas) ▪ chemolithotrophs (e.g., Nitrobacter) ▪ symbionts (e.g., rhizobia)

include diverse aerobic and facultatively aerobic chemoorganotrophs, aerobic anoxygenic phototrophs and a few obligate anaerobes

the largest and most metabolically diverse order of Alphaproteobacteria

metabolize a wide range of organic compounds including many aromatic compounds, potential agents of bioremediation

most species are obligate aerobes or facultative aerobes and many are oligotrophic

are divided into six classes, the Alpha- , Beta- Gamma- Delta- , Epsilon-, and Zetaproteobacteria

are all obligate intracellular parasites or mutualists of animals

contain metabolically diverse, including ▪ purple nonsulfur bacteria e.g., Rhodobacter and Rhodospirillum

leads in numbers of cultivated and well characterized species which accounts for > 33% of characterized species of bacteria

Form root nodules with soybean and other l e g u m e s

▪ free-living nitrogen-fixing bacteria (e.g., Beijerinckia) ▪ plant and animal pathogens (e.g., Agrobacterium tumefaciens also known as Rhizobium radiobacter) ▪ diverse chemoorganotrophs

Obligate intracellular parasites, transmitted by a r t h r o p o d s