Pyrophosphate-Dependent ATP Formation from Acetyl Coenzyme A in Syntrophus aciditrophicus, a New Twist on ATP Formation

Abstract

Syntrophus aciditrophicus is a model syntrophic bacterium that degrades key intermediates in anaerobic decomposition, such as benzoate, cyclohexane-1-carboxylate, and certain fatty acids, to acetate when grown with hydrogen-/formate-consuming microorganisms. ATP formation coupled to acetate production is the main source for energy conservation by S. aciditrophicus. However, the absence of homologs for phosphate acetyltransferase and acetate kinase in the genome of S. aciditrophicus leaves it unclear as to how ATP is formed, as most fermentative bacteria rely on these two enzymes to synthesize ATP from acetyl coenzyme A (CoA) and phosphate. Here, we combine transcriptomic, proteomic, metabolite, and enzymatic approaches to show that S. aciditrophicus uses AMP-forming, acetyl-CoA synthetase (Acs1) for ATP synthesis from acetyl-CoA. acs1 mRNA and Acs1 were abundant in transcriptomes and proteomes, respectively, of S. aciditrophicus grown in pure culture and coculture. Cell extracts of S. aciditrophicus had low or undetectable acetate kinase and phosphate acetyltransferase activities but had high acetyl-CoA synthetase activity under all growth conditions tested. Both Acs1 purified from S. aciditrophicus and recombinantly produced Acs1 catalyzed ATP and acetate formation from acetyl-CoA, AMP, and pyrophosphate. High pyrophosphate levels and a high AMP-to-ATP ratio (5.9 ± 1.4) in S. aciditrophicus cells support the operation of Acs1 in the acetate-forming direction. Thus, S. aciditrophicus has a unique approach to conserve energy involving pyrophosphate, AMP, acetyl-CoA, and an AMP-forming, acetyl-CoA synthetase.

Syntrophus aciditrophicus uses the same enzymes in a reversible manner to degrade and synthesize aromatic and alicyclic acids

“…The current bioenergetic model for energy conservation in S. aciditrophicus involves the unique synthesis of ATP by an AMP‐forming, acetyl‐CoA synthetase (Acs1) (James et al ., ) (Fig. ).…”

“…1. Remarkably, S. aciditrophicus uses a novel approach for ATP synthesis from acetyl-CoA involving an acetyl-CoA synthetase (Acs1), which uses AMP, pyrophosphate and acetyl-CoA to make ATP and acetate, rather than the classical bacterial approach involving phosphate acetyl transferase and acetate kinase (James et al, 2016). However, it is still unclear how net ATP synthesis needed for growth occurs during syntrophic aromatic acid metabolism as aromatic ring reduction and reverse electron transfer needed in hydrogen and formate production are energy-requiring processes (Sieber et al, 2012).…”

Novel energy conservation strategies and behaviour of Pelotomaculum schinkii driving syntrophic propionate catabolism

“…The use of AMP-dependent pyrophosphate-forming acyl-CoA synthetase for substrate activation has also been observed for Syntrophus aciditrophicus during syntrophic benzoate degradation, indicating that P. schinkii shares similarities in biochemical strategies with other syntrophic organisms. In addition, like S. aciditrophicus and Clostridium ultunense (James et al, 2016;Manzoor et al, 2018), P. schinkii may conserve energy from substrate activation by coupling proton extrusion with hydrolysis of the byproduct pyrophosphate via a membrane-bound pyrophosphatase (rank 342nd; Supporting Information Table S4).…”

Genomes of rumen bacteria encode atypical pathways for fermenting hexoses to short‐chain fatty acids

“…If operated in reverse of its normal direction, acetate-CoA ligase could serve as another route for forming acetate from acetyl-CoA (Mai and Adams, 1996;James et al, 2016). However, neither ADP-(Supporting Information Fig.…”