Environmental origin


Other characteristics







Green nonsulfur bacteria and relatives

Actinobacteria (high G + C gram-positives, including actinomycetes) Planctomycetes

Chlamydia Verrucomicrobia




Extreme environments (hot, sulfur pools, thermal vents) Thermal vents

Hot vents and springs; moderate pH and salinity

Anaerobic digesters, cattle manure

Hot environments Wide range but few cultured

Soil, some are pathogens

Soil and water

Intracellular parasites

Freshwater and soil; few cultured

Soil and aquatic environments

Wide range of environments, including soil

Anaerobic environments (termite guts, soil, anaerobic digesters)

Microaerophilic; chemolithotrophic; can oxidize hydrogen and reduced sulfur

Sulfate reducers; autotrophic or organotrophic; anaerobic

Sulfur reducers; organotrophic; some produce hydrogen

Heterotrophic, methanogenic, sulfate reduction


Anoxygenic photosynthesis (Chloroflexus); organotrophic (Thermomicrobium)

Aerobes, heterotrophic—major role in decomposition

Obligate aerobes


Autotrophic nitrite oxidizers, facultative heterotrophs

Acidophilic or anaerobic (very few cultured)


Motile rods; gram-negative cell wall

Prominent cell envelope Rod-shaped cells Degrade xylan

Gram-positive, includes mycelial forms

Flagellated swarmer cells; budding bacteria, ovoid, holdfast, cell wall lacks murein

No peptidoglycan

Spiral shaped

Aquifex aeolicus

Thermodesulfobacterium hydrogeniphilum

Thermotoga maritima

Coprothermobacter platensis

Dictyoglomus thermophilum Chloroflexus, Herpetosiphon, Thermomicrobium roseum

Planctomyces, Pasteuria, Isocystis pallida

Chlamydia psittaci, Trachomatis


Flexistipes Cyanobacteria

Firmicutes (low G + C gram-positive)


Green sulfur bacteria

Bacteroides-Cytophaga-Flexibacter group


Spirochetes and relatives (spirochetes and leptospiras)




Aquatic but found in soil

Soil, water, some are pathogens

Anaerobic and sulfur-containing muds, fresh water and marine

Wide variety, including soil, dung, decaying organic matter

High-temperature environments, nuclear waste

Wide range Pathogens

"Classical" gram-negative bacteria

Oxygenic, photosynthetic; some fix N2

Aerobic or anaerobic (rarely photosynthetic)

Photosynthetic; anaerobic; autotrophic (S oxidation) or heterotrophic

Aerobic, microaerophilic or facultatively anaerobic, organotrophs, some strict anaerobes (Bacteroides)



Heterotrophs; chemolithotrophs; chemophototrophs; anaerobic (most) or aerobic; some photosynthetic; some fix N2

Spiral shaped

Gliding; unicellular, colonial or filamentous

Cocci or rods; includes endospore formers


Aphanocapsa, Oscillatoria, Nostoc, Synechococcus, Gleobacter, Prochloron

Clostridium peptococcus, Bacillus, Mycoplasma

Chlorobium, Chloroherpeton

Gliding (Cytophaga), gramnegative, rods, some pleomorphic, some helical, unbranched filaments

Coccoid, rods; radioresistant or thermophilic; thick cell wall

Motile with flagellum; long, helical, coils; gram-negative

Gram-negative cell wall Often motile (flagella or gliding); gram-negative cell wall structure

Flavobacterium, Sphingobacterium, Cytophaga, Saprospira bacteroides, Prevotella, Porphyromonas

Deinococcus radiodurans, Thermus aquaticus

Spirochaeta, Treponema, Borrelia, Leptospira, Leptonema

Rhizobacterium, Agrobacterium, Rickettsia, Nitrobacter, Pseudomonas, Nitrosomonas, Thiobacillus, Alcaligenes, Spirillum, Nitrosospira, Legionella (some), Beggiatoa, Desulfovibrio, Myxobacteria, Bdellovibrio

Some groups are represented by many cultivated organisms. In general, these are found in a wide range of habitats and exhibit a diversity of physiological and morphological characteristics. Other groups are represented by very few cultivated strains and the range of environments and physiologies listed above is likely to expand as additional environments are explored and isolation techniques improve.

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