[This corrects the article on p. 100 in vol. 41.].

Energy conservation in chemotrophic anaerobic bacteria.

http://hoffman.cm.utexas.edu/courses/wood_lungdahl_1.pdf

Acetogenesis and the Wood-Ljungdahl Pathway of CO2 Fixation

Acetogens utilize the acetyl-CoA Wood-Ljungdahl pathway as a terminal electron-accepting, energy-conserving, CO(2)-fixing process. The decades of research to resolve the enzymology of this pathway (1) preceded studies demonstrating that acetogens not only harbor a novel CO(2)-fixing pathway, but are also ecologically important, and (2) overshadowed the novel microbiological discoveries of acetogens and acetogenesis. The first acetogen to be isolated, Clostridium aceticum, was reported by Klaas Tammo Wieringa in 1936, but was subsequently lost. The second acetogen to be isolated, Clostridium thermoaceticum, was isolated by Francis Ephraim Fontaine and co-workers in 1942. C. thermoaceticum became the most extensively studied acetogen and was used to resolve the enzymology of the acetyl-CoA pathway in the laboratories of Harland Goff Wood and Lars Gerhard Ljungdahl. Although acetogenesis initially intrigued few scientists, this novel process fostered several scientific milestones, including the first (14)C-tracer studies in biology and the discovery that tungsten is a biologically active metal. The acetyl-CoA pathway is now recognized as a fundamental component of the global carbon cycle and essential to the metabolic potentials of many different prokaryotes. The acetyl-CoA pathway and variants thereof appear to be important to primary production in certain habitats and may have been the first autotrophic process on earth and important to the evolution of life. The purpose of this article is to (1) pay tribute to those who discovered acetogens and acetogenesis, and to those who resolved the acetyl-CoA pathway, and (2) highlight the ecology and physiology of acetogens within the framework of their scientific roots.

/pdf/old-acetogens-new-light-21l5wceyq5.pdf

Old Acetogens, New Light

Homoacetogenesis during hydrogen production by mixed cultures dark fermentation: Unresolved challenge

A strictly anaerobic, gram-positive, sporeforming, rod-like, motile bacterium was enriched from rabbit feces, and isolated using carbon monoxide as sole source of energy and carbon. The isolate metabolizes CO with ethanol, acetate and CO2 as end-products. Other substrates used as carbon and energy sources include CO2 plus H2, pyruvate, xylose, arabinose, fructose, rhamnose, and l-glutamate. The optimum temperature for growth is 37°C. The optimum pH for chemolithotrophic growth lies around 5.8 to 6.0 Sulfate is not reduced. Growth is inhibited either by penicillin, chloramphenicol, tetracyclin or ampicillin, each at 100 μg per ml. The isolate has a DNA-base composition of 25.9±0.6% guanine plus cytosine. The isolate represents a new species of Clostridium for which the name Clostridium autoethanogenum is proposed. The type strain is strain JA1-1

Clostridium autoethanogenum, sp. nov., an anaerobic bacterium that produces ethanol from carbon monoxide

A new species—Clostridium formicoaceticum—is described. It ferments fructose and several hexonic and hexuronic acids to acetate and formate. During active growth acetate is the main product of the fermentation. Considerable quantities of formate appear among the fermentation products in the stationary growth phase.

J. R. Andreesen

Papers

Clostridium formicoaceticum nov. spec. Isolation, description and distinction from C. aceticum and C. thermoaceticum