Microbes and Plants - Freshwater Ecology: Concepts and Environmental Applications - page 130

Genera represented in aquatic

Major group Group systems (No. of described genera) Importance

Gram-negative with cell wall Spriochetes Spirochaeta (8 ) Free living in aquatic waters, some pathogens

Aerobic/microerophlic, motile, Campylobacter, Bdellovibrio (16) In freshwaters, some denitrifiers, includes the

hilical/vibriod predatory Bdellovibrio

Nonmotile curved Ancylobacter (8) In freshwater

Aerobic/microaerophilic rods and cocci Azotobacter, Aerobic nitrogen fixation (e.g., Azotobacter ),

Psuedomonas, Francisella, Legionella (84) some disease organisms, very diverse group

Facultative anaerobic rods Escherichia, Vibrio (45) Contains many waterborne disease organisms

Anaerobic straight, curved, and helical rods Thermotoga (47) Common from anoxic muds and animal intestinal tracts,

also many thermophiles and halophiles

Dissimilatory sulfur reducing Desulfomonas (18) Reduces oxidized sulfur compounds to sulfide

Anaerobic cocci Megashaera (4) Mainly animal parasites

Rickettsias and chlamydias Two subgroups Parasites

Anoxygenic photosynthetic Rhodospirillum (28 ) Able to use sulfide as electron donor for photosynthesis

Oxygenic photosynthetic Cyanobaceteria (37) Important photosynthetic and nitrogen fixers

Aerobic chemilithotrophic Thermothrix, Nitrobacter (28) Important biogeochemically, including

nitrifiers, iron oxidizers, and sulfur oxidizers

Budding or appendages Caulobacter (25) Caulobacter indicative of oligotrophic conditions

Sheathed Clonothrix (7) Some important in iron and manganese cycles

Gliding, nonphotosynthetic, nonfruiting Beggiatoa (28) Mostly aquatic, some important in sulfur cycling

Myxobacteria Polyangium (12) Decomposers, predominantly in soils but some

freshwaters

Gram positive with cell walls Cocci Streptococcus, Trichhococcus (24) Some pathogens, also found in aquatic habitats

Endospore forming Bacillus (10) Widespread species, some sulfur oxidizers

Nonsporing regular rods Lactobacillus (8) Widespread, some fish pathogens

Nonsporing irregular rods Microbacterium (36) An artificial group, some pathogens, mainly in

soil, some aquatic thermophiles

Mycobacteria Mycobacterium (1) Widely distributed in soil and water, some pathogens

Actinomyctes Dactylosporangium, Streptomyces (49) Fungi-like morphology, important in

decomposition in soils

No cell wall, Bacteria Mycoplasmas Mycoplasma (6) Smallest known self-reproducing organisms, ecology poorly

known

Archaea Methanogens Methanobacterium (18) Generates methane

Sulfate reducers Archaeoglobus (1) Deep-sea vents

Extreme halophiles Halobacterium (6) Require at least 1.5 M NaCl for growth

Cell wall-less Thermoplasma (1) Found in mine waste

Extreme thermophiles Sulfolobus (14) Optimum growth at 70-105 C

a The number of described genera is only included as a rough guide to relative diversity in the group.