Project description:Purpose: To understand the adaptive mechanisms of Methanocellales to low H2 and syntrophic growth. Methods: We analyzed the transcriptomes of M. conradii and P. thermopropionicum under monoculture and syntrophic coculture conditions by strand specific mRNA sequencing using Illumina Hiseq 2000. Four biological replicates were sequenced. The sequence reads that passed quality filters were analyzed by Burrows–Wheeler Aligner (BWA) followed by HTSeq and DESeq2. qRT–PCR validation was performed using SYBR Green assays Results: The results showed that M. conradii and P. thermopropionicum interacted closely and synchronized their gene transcription during the syntrophic growth. In coculture, M. conradii and P. thermopropionicum significantly enhanced the transcription of genes related to energy conservation processes, including methanogenesis, propionate degradation and electron bifurcation. By contrast, the genes coding for biosynthesis steps were downregulated in both M. conradii and P. thermopropionicum during the syntrophic growth. The physiology experiment showed that formate but not H2 inhibited syntrophic oxidation of propionate. Accordingly, formate dehydrogenase-encoding genes in both M. conradii and P. thermopropionicum were markedly upregulated, indicating that formate plays an important role in the interspecies electron transfer between M. conradii and P. thermopropionicum in coculture. Conclusions: our study provides abundant transcriptome data indicating the adaptations of Methanocella spp. to H2 limitation and suggests that flavin based electron bifurcations are critical to the syntrophic growth in both M. conradii and P. thermopropionicum.
Project description:Propionate accumulation is an important bottleneck for anaerobic degradation of organic matter. We hypothesized that propionate conversion by a novel coculture of Syntrophobacter fumaroxidans and Geobacter sulfurreducens can be an alternative strategy for propionate oxidation coupled to Fe(III) reduction. In this study, we successfully cocultured S. fumaroxidans and G. sulfurreducens on propionate and Fe(III). Proteomic analyses of this coculture provided insights into the underlying mechanisms of propionate metabolism pathway and interspecies electron transfer mechanism. Our study can be further useful in understanding syntrophic propionate degradation in bioelectrochemical and anaerobic digestion systems.
Project description:In the syntrophic interaction between fermentative bacteria (Pelotomaculum thermopropionicum) and methanogenic archaea (methanogens: Methanothemobacter thermautotrophicus), reducing equivalents (e.g., H2) produced by fermentative bacteria should efficiently be consumed by methanogens in order for the fermentation of volatile fatty acids (VFA, e.g., butyrate, propionate, and acetate) to be thermodynamically feasible. It has been known that physical approximation (e.g., coaggregation) between VFA-fermenting syntrophic bacteria (syntrophs) and hydrogenotrophic methanogens is necessary for efficient H2 transfer between them. Our previous study has shown that, at an early exponential growth phase of syntrophic coculture, cells of Pelotomaculum thermopropionicum (syntroph) were connected to cells of Methanothermobacter thermautotrophicus (methanogen) via unidentified extracellular filamentous appendages, after which they started to coaggregate, suggesting that the filamentous appendages may have been important for their syntrophic interaction. The filamentous appendages seemed to specifically connect these syntrophic partners, since such pairwise connection has been observed neither in single-species cultures (monocultures) nor in mixtures with other microbes.<br>We found that P. thermopropionicum has putative gene clusters for flagellum and pilus, while no extracellular filament gene was identified in the M. thermautotrophicus genome. So we examined transcriptome responses of M. thermautotrophicus to the contact with flagellar filament protein (FliC) and flagellar cap protein (FliD) of P. thermopropionicum.
Project description:In the syntrophic interaction between fermentative bacteria (Pelotomaculum thermopropionicum) and methanogenic archaea (methanogens: Methanothemobacter thermautotrophicus), reducing equivalents (e.g., H2) produced by fermentative bacteria should efficiently be consumed by methanogens in order for the fermentation of volatile fatty acids (VFA, e.g., butyrate, propionate, and acetate) to be thermodynamically feasible. It has been known that physical approximation (e.g., coaggregation) between VFA-fermenting syntrophic bacteria (syntrophs) and hydrogenotrophic methanogens is necessary for efficient H2 transfer between them. Our previous study has shown that, at an early exponential growth phase of syntrophic coculture, cells of Pelotomaculum thermopropionicum (syntroph) were connected to cells of Methanothermobacter thermautotrophicus (methanogen) via unidentified extracellular filamentous appendages, after which they started to coaggregate, suggesting that the filamentous appendages may have been important for their syntrophic interaction. The filamentous appendages seemed to specifically connect these syntrophic partners, since such pairwise connection has been observed neither in single-species cultures (monocultures) nor in mixtures with other microbes. <br> We found that P. thermopropionicum has putative gene clusters for flagellum and pilus, while no extracellular filament gene was identified in the M. thermautotrophicus genome. So we examined transcriptome responses of M. thermautotrophicus to the contact with flagellar filament protein (FliC) and flagellar cap protein (FliD) of P. thermopropionicum.
