Syntrophy in anaerobic global carbon cycles

Abstract

Summary of recent advances Syntrophy is an essential intermediary step in the anaerobic conversion of organic matter to methane where metabolically distinct microorganisms are tightly linked by the need to maintain the exchanged metabolites at very low concentrations. The need for syntrophy is thermodynamically constrained, and is probably a prime reason why it is difficult to culture microbes as these approaches disrupt consortia. Reconstruction of artificial syntrophic consortia has allowed uncultured syntrophic metabolizers and methanogens to be optimally grown and studied biochemically. The pathways for syntrophic acetate, propionate and longer chain fatty acid metabolism are mostly understood, but key steps involved in benzoate breakdown and cyclohexane carboxylate formation are unclear. Syntrophic metabolism requires reverse electron transfer, close physical contact, and metabolic synchronization of the syntrophic partners. Genomic analyses reveal that multiple mechanisms exist for reverse electron transfer. Surprisingly, the flagellum functions were implicated in ensuring close physical proximity and synchronization of the syntrophic partners.

Straw- and slurry-associated prokaryotic communities differ during co-fermentation of straw and swine manure

“…To alleviate this effect, transformation of VFAs through syntrophic metabolism is essential. Syntrophy, an indispensable process linking fermentation and methanogenesis, can overcome unfavorable thermodynamics for the degradation of organic matter under methanogenic condition (McInerney et al 2009). Most syntrophs are affiliated with the phyla Firmicutes, Proteobacteria, and Synergistetes, e.g., the genera Pelotomaculum, Syntrophobacter, Syntrophus, Syntrophomonas, Desulfovibrio, Geobacter, Aminobacterium, and Aminomonas (Sieber et al 2012).…”

Segregating metabolic processes into different microbial cells accelerates the consumption of inhibitory substrates

“…Substrate cross-feeding occurs when one cell type partially consumes a primary substrate into a metabolic intermediate and another cell type then further consumes the intermediate. Substrate cross-feeding controls numerous environmentally and economically important microbial processes, including the mineralization of organic carbon (Schink, 1997;McInerney et al, 2009), the degradation of environmental contaminants (de Souza et al, 1998;Møller et al, 1998;Pelz et al, 1999;Drzyzga and Gottschal 2002;Holmes et al, 2006) and the recycling of fixed nitrogen into dinitrogen gas (N 2 ) (Martienssen and Schops, 1999;Van de Pas-Schoonen et al, 2005;Costa et al, 2006). While substrate cross-feeding is frequently observed within natural and engineered microbial communities, its effects on microbial processes are often unclear.…”

Reach out and touch someone: potential impact of DIET (direct interspecies energy transfer) on anaerobic biogeochemistry, bioremediation, and bioenergy

“…It can clearly be shown in the laboratory that microorganisms that produce hydrogen from the anaerobic degradation of various organic substrates can grow in co-culture with hydrogen-consuming methanogens and, in fact, the hydrogen-producers generally require the methanogens to remove hydrogen in order to make continued hydrogen production thermodynamically feasible (McInerney et al 2009;Stams and Plugge 2009 (Ozturk et al 1989). Now, it is apparent that another possibility must also be considered.…”

“…A microorganism that can gain energy from the oxidation of the hydrogen then consumes it. Since first proposed over 40 years ago (Bryant et al 1967), interspecies hydrogen transfer has been considered to be central to the production of methane gas in anaerobic soils, sediments, and animal intestinal systems (McInerney et al 2009;Stams and Plugge 2009). The positive benefit is effective anaerobic metabolism of organic matter in these environments.…”

“…For example, one of the best-known examples of interspecies cooperation is interspecies hydrogen transfer, which is a strategy for microorganisms to exchange electrons (McInerney et al 2009;Stams and Plugge 2009). A microorganism that needs to release electrons, derived from the oxidation of an organic substrate, reduces protons with those electrons, producing hydrogen gas.…”