Growth- and substrate-dependent transcription of formate dehydrogenase and hydrogenase coding genes in Syntrophobacter fumaroxidans and Methanospirillum hungatei

Abstract

Transcription of genes coding for formate dehydrogenases (fdh genes) and hydrogenases (hyd genes) in Syntrophobacter fumaroxidans and Methanospirillum hungatei was studied following growth under different conditions. Under all conditions tested, all fdh and hyd genes were transcribed. However, transcription levels of the individual genes varied depending on the substrate and growth conditions. Our results strongly suggest that in syntrophically grown S. fumaroxidans cells, the [FeFe]-hydrogenase (encoded by Sfum_844-46), FDH1 (Sfum_2703-06) and Hox (Sfum_2713-16) may confurcate electrons from NADH and ferredoxin to protons and carbon dioxide to produce hydrogen and formate, respectively. Based on bioinformatic analysis, a membrane-integrated energy-converting ,-methylene-H 4 MPT reduction are the cytoplasmic [NiFe]-hydrogenase and FDH1. 16S rRNA ratios indicate that in one of the triplicate co-cultures of S. fumaroxidans and M. hungatei, less energy was available for S. fumaroxidans. This led to enhanced transcription of genes coding for the Rnf-complex (Sfum_2694-99) and of several fdh and hyd genes. The Rnf-complex probably reoxidized NADH with ferredoxin reduction, followed by ferredoxin oxidation by the induced formate dehydrogenases and hydrogenases.

Variation among Desulfovibrio Species in Electron Transfer Systems Used for Syntrophic Growth

“…Diffusion kinetics based on Fick's law showed that interspecies formate transfer could sustain a 100-fold higher conversion rate than interspecies hydrogen transfer (7,8). Indeed, several studies have indicated the importance of formate as an electron shuttle in propionate-and butyrate-oxidizing syntrophs (3,(5)(6)(7)(8)(9)(10)(11). However, to our knowledge, this is the first description of its involvement in lactate oxidation of syntrophic Desulfovibrio species.…”

“…Additionally, single reports suggest the involvement of cysteine or exogenous carriers such as humic substances (2) as well as the existence of a direct electron transfer via electrically conductive pili called nanowires (4). Exclusive use of hydrogen as an electron carrier has been proven for several syntrophs, while a simultaneous formate/H 2 electron shuttle was proposed to be operative in propionate-and butyrate-degrading cocultures on the basis of early physiological experiments (2,(5)(6)(7)(8)(9) and later confirmed by biochemical and genetic studies (10,11). Indeed, the midpoint redox potentials (E°=) of the redox couples H 2 -H ϩ and formate-CO 2 are similar (Ϫ414 mV and Ϫ432 mV, respectively) (12), but hydrogen and formate have different chemical and physical properties.…”

“…So far, most biochemical and genetic studies have focused on the investigation of the electron transfer and energy conservation mechanisms in propionate and butyrate oxidizers, e.g., Syntrophobacter and Syntrophomonas (3,5,6,10,11), while there is only limited understanding of the syntrophic metabolism of other representative bacterial species, e.g., Desulfovibrio (17)(18)(19).…”

Correlation between microbial community and granule conductivity in anaerobic bioreactors for brewery wastewater treatment

“…The possible role of the Syntrophobacter species is to metabolize propionate to acetate with transfer of reducing equivalents to methanogens (Sieber et al, 2012). Gene expression studies (Worm et al, 2011) and genome analysis (Sieber et al, 2012) have provided strong evidence that the transfer of reducing equivalents between Syntrophobacter species and methanogens proceeds via H 2 and formate. Therefore, Syntrophobacter species are not expected to participate in DIET.…”

Flexibility of Syntrophic Enzyme Systems in Desulfovibrio Species Ensures Their Adaptation Capability to Environmental Changes

“…Hydrogen and formate are considered to be the primary shuttle compounds for interspecies electron transfer in methanogenic consortia (1)(2)(3). Exclusive use of H 2 as an electron carrier has been proven for several syntrophs, while a combined formate/H 2 electron shuttling has been confirmed in propionate-and butyrate-degrading cocultures (2,(4)(5)(6)(7)(8)(9)(10). Since syntrophic communities exist in conditions close to thermodynamic equilibrium and metabolite exchange is considered to occur primarily via diffusion (1)(2)(3)(4)11), intermicrobial distances influence the efficiency of interspecies transfer (especially for H 2 ), which affects the growth and biodegradation rates of these consortia (2,6,(11)(12)(13).…”