Old Acetogens, New Light

Abstract

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.

Methanogenic food web in the gut contents of methane-emitting earthwormEudrilus eugeniaefrom Brazil

“…C. mayombei can also convert succinate to propionate and CO 2 (Kane et al, 1991). The capacity of acetogens to utilize a variety of electron donors and electron acceptors (Drake et al, 2008) reinforce the likelihood that acetogens could be metabolically active in the complex milieu of the gut contents of E. eugeniae.…”

“…However, which source of reductant (H 2 or formate) was used for methanogenesis remains unclear. Four molecules of H 2 or four molecules of formate are needed to produce one molecule of CH 4 (Hedderich and Whitman, 2006 Four molecules of formate are required to synthesize one molecule of acetate via acetogenesis (Drake et al, 2008). Thus approximately 9 mmol acetate per gram FW could have been formed from the approximate 34 mmol formate per gram FW transiently formed from glucose in [ 13 C]-glucose treatments.…”

Metagenomics analysis of methane metabolisms in manure fertilized paddy soil

“…1B). Acetogenic bacteria, including Holophaga foetida, Moorella thermoacetica, Oxobacter pfennigii, Thermoanaerobacter kivui (Muller, 2003;Drake et al, 2008;Fenchel, 2011;Müller and Frerichs, 2013), are possible substrate producers to acetoclastic methanogens. In this study, acetogenic bacteria were identified only in PIG sample (Fig.…”

A review of conversion processes for bioethanol production with a focus on syngas fermentation

“…This microorganism was used to determine the acetyl-CoA pathway enzymology in the laboratories of Harland Goff Wood and Lars Gerhard Ljungdahl (Drake et al, 2008). To date, there are more than 100 acetogenic species isolated from a variety of habitats such as sediments, soils, sludge, and intestinal tracts of animals (Drake et al, 2008). Most of the microorganisms currently known to ferment syngas to ethanol are predominantly mesophilic with operating temperatures in the range of 30-40 °C (Munasinghe and Khanal, 2010a).…”

“…This microorganism was used to determine the acetyl-CoA pathway enzymology in the laboratories of Harland Goff Wood and Lars Gerhard Ljungdahl (Drake et al, 2008). To date, there are more than 100 acetogenic species isolated from a variety of habitats such as sediments, soils, sludge, and intestinal tracts of animals (Drake et al, 2008).…”