58 4 Taxonomy, Physiology, and Ecology of Aquatic Microorganisms
- Thermodesulfobacterium
Thermodesulfobacterium is a thermophilic sulfate
reducer. Sulfate reducers include a wide range of
morphological types, including rods, vibrios,
ovals, spheres, and even teardropped or onion
shaped cells. Some are motile, others are not. Most
sulfatereducing bacteria are mesophilic, but a few
are thermophiles, among which is the Gram nega
tive and anaerobic Thermodesulfobacterium. The
bacterium is nonsporeforming. It is an aquatic
organism and has been isolated from volcanic hot
springs, deepsea hydrothermal sulfides, and other
marine environments. In marine sediments and in
aerobic wastewater treatment systems, sulfate
reduction accounts for up to 50% of the mineral
ization of organic matter. Furthermore, sulfate
reduction strongly stimulates microbially enhanced
corrosion of metals. Sulfate Reducing Bacteria
(SRB) are discussed in more detail later. - Thermotoga
Thermotoga is typically a rodshaped cell envel
oped in an outer cell membrane (the “toga” or
jacket). Thermotoga enzymes are known for being
active at high temperatures. Enzymes from
Thermotoga spp. are extremely thermostable and
therefore, useful for many industrial processes
such as in the chemical and food industries. The
organisms are thermophilic or hyperthermophilic,
growing best around 80°C and in the neutral pH
range. The salt tolerance of Thermotoga species
varies greatly; while some display an extremely
high salt tolerance, others are restricted to low
salinity habitats. This aerobic Gramnegative
organism is typically nonsporeforming and
metabolizes several carbohydrates, both simple
and complex, including glucose, sucrose, starch,
cellulose, and xylan. It can grow by anaerobic res
piration using H 2 as electron donor and Fe3+ as
electron acceptor. It is found in hot springs and in
the hydrothermic vents of ocean floors. Thermotoga
maritime has been widely studied. - Green nonsulfur bacteria (Chloroflexi)
The Green nonsulfur bacteria are now known as
Chloroflexi are typically filamentous, and can move
about by bacterial gliding. They are facultatively
aerobic and have a different method of carbon fixa
tion (photoheterotrophy) from other photosynthetic
bacteria. Like green plants, they also carry out pho
Fig. 4.9 Illustrations of some bacteria (All items in table repro
duced with permission)