GREEN SULFUR BACTERIA
|Photolithotrophic and Anaerobic||Straight or curved rods to star-like extrusions, some spiral forms (aquatic)||Cells strain gram negative||Permanently immotile||Colonies are green, and brown(if carotenoids are present)|
|Nitrogen fixation||No unusual structures formed||Growth in high temperatures and high salinity||No resting stages or spores known|
In the above pictures, the left one shows a photomicrograph of Prosthecochloris aestaurii, x 2300. The second picture (center) shows Chlorobium limicola, x 1500; note the extracellular sulfur granules. The third image (right) shows an unidentified spiral form. These are good examples of representative Green Sulfur bacteria
Green Sulfur bacteria are found in anaerobic conditions such as muds and anoxic waters. The bacteria are found most often under the Purple Sulfur bacterial layer. Most forms of Green Sulfur are green, hence the name, but some strains have a brown tint. These bacteria are photolithotrophic as well as anaerobic. They are capable of using sulfide or elemental S as the electron donor. The elemental S arises from H2S oxidation and is deposited extracellularly, before the oxidation of sulfate.
There are four genera of green sulfur bacteria, Chlorobium, Prosthecohloris, Pelodictyon, and Clathrochloris.
Genera of green sulfur bacteria.
|Green sulfur bacteria||Cell Form and Arrangement||Motility||Vacuoles||Prosthecae|
|Chlorobium||Straight or curved rods, single or short chains||No||No||No|
|Prosthecochloris||Ovoid, single, or short chains||No||No||Yes|
|Pelodictyon||Chains of rods, forming nets||No||Yes||No|
|Clathrochloris||Chains of rods in loose, trellislike aggregates||Yes||No||No|
The Green Sulfur bacteria strains are green because of the presence of chlorophyll c and d and small traces of a. The green sulfur bacteria are found in anaerobic and sulfide-containing fresh or marine waters, and wetlands. The bacterial strains that demonstrate a brown color contain bacteriochlorophyll e and isorenieratane. These strains are found in the deeper layers of wetlands and water. Both of the two groups can be found also living in extreme conditions of salinity and high temperatures. The morphology of both color types is most often either straight or curved rods.
The oxidation of sulfide to sulfate occurs by the means of either phototrophic or chemotrophic bacteria.
Adelberg, Edward. 1976. The Microbial World. Prentice-Hall Inc. New York
Case, Christine. 1995. Microbiology. Addison and Wesley Publishing Co. New York.
Clark, F.E. 1996. Soil Microbiology and Biochemistry. Academic Press. New York.
Norton, Cynthia. 1981. Microbiology. Benjamin/Cummings Publishing Co. Readiing, Mass.
These sites contain additional information on the genera of green sulfur bacteria.