Thermoanaerobium brockii
Emily Mills
The genus Thermoanaerobium consists of two species, T. brockii and T. lactoethylicum. This genus is closely related to the genus Thermoanaerobacter. They share a common optimal temperature range from 60-70oC. These genera also share a similar morphology, habitat, and energy-yielding metabolic pathways with one another and some thermophilic Clostridium species. The species of these genera have different Gram-stain reactions, pH range, sulfur metabolism, cell size, and end-product ratios. These genera were used to specify the first thermophilic, anaerobic, rod-shaped, Gram-positive, non-sporeforming bacteria that yield ethanol and lactate as main saccharide fermentation products.

Thermoanaerobium brockii was discovered by J. Gregory Zeikus in 1979, Many types of thermophilic bacteria are common in self-heating soils and sediments, and in volcanic habitats. Thermoanaerobiumbrockii strains, along with Clostridium thermosulfurogenes and Clostridium thermohydrosulfuricum, have been isolated from different hot spring environments. for example is the Octopus Spring in Yellowstone National Park in Wyoming.
The basal medium for enrichment and isolation of Thermoanaerobium brockii has a pH of 7.2-7.4. In the culture medium gas phase, 95% N2 and 5% C02 are used. Yeast extract and other ingredients are sterilized separately and used as supplements for the basal medium. Strains of Thermoanaerobium and Thermoanaerobacter can be kept at room temperature for days, but for them to be kept for long-term, the cultures should be stored in 20-30% glycerol at -70oC or lyophilized.

The growth of the different species is inhibited by oxygen, penicillin, cycloserine, streptomycin, tetracycline, and chloramphenicol. Looking at the enzymes and metabolic pathways of these two genera show that the various species can use the same general pathways for energy conservation during glucose fermentation. They also produce the same end products; ethanol, lactate, acetate, and H2 plus C02 - One of the main differences in species is the ratio of ethanol to lactate. An example of this is, in Thermoanaerobacter ethanolicus, ethanol is the major product of glucose fermentation, while lactate is the major product in T. brockii. It was shown in 1980 by Lamed and Zeikus that per mole of glucose, 0.95 mol of ethanol was produced by T. brockii in media containing 0.5% glucose and 0.05% yeast extract. The fermentation was shifted in favor of lactate when the extract concentration was raised to 0.1%. When glucose concentrations exceeded 1.5%, growth, of T. brockii was inhibited.

T. brockii had both NAD- and NADP- dependent alcohol dehydrogenase activities. It has fructose-1-6-bisphosphate activated lactate dehydrogenase. The NAD-linked enzyme is very sensitive to oxygen. It may be considered unsuitable for ethanol production. This has mostly to do with the low ethanol and high lactate yields. Studies of the metabolic pathways of T. brockii have shown that ethanol yields can be enhanced, by altering the normal electron flow during saccharide fermentation. It can also be done, by altering lactate dehydrogenase activity.

Reference:
The Prokaryotes. Balows, A., Truper, H.G., Dworkin, M., Harder, W., Schleifer, K.-H. "The Genera Thermoanaerobacter, Thermoanaerobium, and other Thermoanaerobic Saccharolytic Bacteria of Uncertain Taxonomic Affiliation." Jain, Mahendra K., Zeikus, Gregory J. Vol. II. Springer-Verlag New York Inc. p. 1901-11.

*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.

 

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