The acetyl-CoA pathway of autotrophic growth

Abstract

The most direct conceivable route for synthesis of multicarbon compounds from CO: is to join two molecules of CO 2 together to make a 2-carbon compound and then polymerize the 2-carbon compound or add CO 2 successively to the 2-carbon compound to make multicarbon compounds. Recently, it has been demonstrated that the bacterium, Clostridium thermoaceticum, grows autotrophically by such a process. The mechanism involves the reduction of one molecule of CO 2 to a methyl group and then its combination with a second molecule of CO2 and CoA to form acetyl-CoA. We have designated this autotrophic pathway the acetyl-CoA pathway [1]. Evidence is accumulating that this pathway is utilized by other bacteria that grow with CO 2 and H 2 as the source of carbon and energy. This group includes bacteria which, like C. thermoaceticum, produce acetate as a major end product and are called acetogens or acetogenic bacteria. It also includes the methaneproducing bacteria and sulfate-reducing bacteria.The purpose of this review is to examine critically the evidence that the acetyl-CoA pathway occurs in other bacteria by a mechanism that is the same or similar to that found in C. thermoaceticum. For this purpose, the mechanism of the acetyl-CoA pathway, as found in C. thermoaceticum, is described and hypothetical mecha-nims for other organisms are presented based on the acetyl-CoA pathway of C. thermoaceticum. The available data have been reviewed to determine if the hypothetical schemes are in accord with presently known facts. We conclude that the formation of acetyl-CoA by other acetogens, the methanogens and sulphate-reducing bacteria occurs by a mechanism very similar to that of C.therrnoaceticum.

Factors controlling 13C contents of sedimentary organic compounds: Principles and evidence

“…Green photosynthetic bacteria (the Chlorobiaceae) fix carbon mainly by reversing the tricarboxylic acid cycle (Sirevag et al, 1977). Together with nonphotosynthetic bacteria that can grow autotrophically while fixing carbon and constructing biomass by use of the "acetyl-CoA pathway" (i.e., acetogenic and methanogenic bacteria, Wood et al, 1986), they form a subset of organisms in which carbon is . Schematic views of the the differing pathways by which carbon is supplied to biosynthetic reaction networks.…”

Transformation of tetra- and trichloromethane to CO2 by anaerobic bacteria is a non-enzymic process

“…Two types of reactions have been recognized: reductive, to less-highly chlorinated methanes, and substitutive, to CO 2 and some of its transformation products [4][5][6]. The ability to anaerobically transform CCI 4 has been correlated [5] with the presence of the acetyI-CoA pathway [7,8] for the degradation or synthesis of acetate (acetyI-CoA) in these organisms. Bacteria with an operative acetyi-CoA pathway contain high levels of corrinoids [9.10], and it has been suggested that the latter catalyze reductive dehalogenation in anaerobic bacteria [5,11].…”

5′‐Methylbenzimidazolyl‐cobamides are the corrinoids from some sulfate‐reducing and sulfur‐metabolizing bacteria

“…In analogy to the role of the corrins in methanogens [4,40] and in acetogens [3,41], in this eubacterial sulfate reducer the rather abundant corrins presumably participate as Cop-methyl-derivatives in the crucial acetyl-CoA C-C bound-forming or cleavage steps. The high amounts of cobamides found in the eubacterium D. propionicus and in the archaebacterium A.fulgidus [30,31] also suggest a central role of the corrins in these sulfate reducers.…”