Syntrophic Growth of Desulfovibrio alaskensis Requires Genes for H ₂ and Formate Metabolism as Well as Those for Flagellum and Biofilm Formation

Abstract

In anaerobic environments, mutually beneficial metabolic interactions between microorganisms (syntrophy) are essential for oxidation of organic matter to carbon dioxide and methane. Syntrophic interactions typically involve a microorganism degrading an organic compound to primary fermentation by-products and sources of electrons (i.e., formate, hydrogen, or nanowires) and a partner producing methane or respiring the electrons via alternative electron accepting processes. Using a transposon gene mutant library of the sulfate-reducing Desulfovibrio alaskensis G20, we screened for mutants incapable of serving as the electron-accepting partner of the butyrate-oxidizing bacterium, Syntrophomonas wolfei. A total of 17 gene mutants of D. alaskensis were identified as incapable of serving as the electron-accepting partner. The genes identified predominantly fell into three categories: membrane surface assembly, flagellum-pilus synthesis, and energy metabolism. Among these genes required to serve as the electron-accepting partner, the glycosyltransferase, pilus assembly protein (tadC), and flagellar biosynthesis protein showed reduced biofilm formation, suggesting that each of these components is involved in cell-to-cell interactions. Energy metabolism genes encoded proteins primarily involved in H 2 uptake and electron cycling, including a rhodanese-containing complex that is phylogenetically conserved among sulfate-reducing Deltaproteobacteria. Utilizing an mRNA sequencing approach, analysis of transcript abundance in wild-type axenic and cocultures confirmed that genes identified as important for serving as the electronaccepting partner were more highly expressed under syntrophic conditions. The results imply that sulfate-reducing microorganisms require flagellar and outer membrane components to effectively couple to their syntrophic partners; furthermore, H 2 metabolism is essential for syntrophic growth of D. alaskensis G20.A naerobic oxidation of organic compounds, such as alcohols and fatty acids, is thermodynamically unfavorable when protons or carbon dioxide are used as the electron acceptor, unless the H 2 partial pressure or formate concentration, respectively, can be maintained at extremely low concentrations (1). Thus, complete degradation of organic matter in methanogenic and some other anaerobic systems requires a microbial consortium composed of two or more microbial species to oxidize the carbon and subsequently remove hydrogen (2-5). This synergistic interaction between different microorganisms is defined as syntrophy. The term was first coined in anaerobic, sulfur-oxidizing phototrophic cocultures (6) but was experimentally verified when the methanogenic, archaean Methanobacterium bryantii strain MOH was separated from an ethanol-oxidizing partner, both of which were present in a culture called Methanobacillus omelianskii, which at the time was believed to be a pure culture (7). This work established the general syntrophic model of two microorganisms mutualistically cooperating by transferring electron...

Targeted in situ metatranscriptomics for selected taxa from mesophilic and thermophilic biogas plants

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A Post-Genomic View of the Ecophysiology, Catabolism and Biotechnological Relevance of Sulphate-Reducing Prokaryotes

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Gypsum amendment to rice paddy soil stimulated bacteria involved in sulfur cycling but largely preserved the phylogenetic composition of the total bacterial community

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