Project description:Conversion of biomass-derived syngas (gaseous mixture of mainly H2, CO and CO2) to methane might be a sustainable alternative for the biofuel industry. Via the syngas route more methane can be produced from biomass than via conventional anaerobic digestion. Methanogenic archaea are key players in syngas conversion, but only a few are known to utilize CO (or syngas). Methanothermobacter thermoautotrophicus is one of the few hydrogenotrophic methanogens which has been observed to grow on CO. However, carboxydotrophic growth is slow and is reported to be readily inhibited above 50 kPa CO. The aim of this work was to get more insight of the CO metabolism in hydrogenotrophic archaea and to assess the potential toxic effects of CO towards these microorganisms. Archaeal genomic databases were searched for putative homologues of the Methanothermobacter thermoautotrophicus CODH alpha subunit (containing the catalytic site): the highest scores were for the CODH subunits of Methamothermobacter marburgensis (93% identity) and Methanococcus maripaludis (71%). M. thermoautotrophicus and the other two potential carboxydotrophic strains were incubated with CO and CO + H2 as sole substrates. In addition to M. thermoautotrophicus, M. marburgensis was able to grow methanogenically on CO alone and on CO + H2. In contrast to M. thermoautotrophicus, M. marburgensis was not as strongly inhibited when grown in presence of CO alone and was able to adapt its metabolism, shifting its lag phase from ~500 to ~100 hours. It was observed for both strains that presence of hydrogen stimulates the carbon monoxide metabolism. To gain further insight, the proteome of M. marburgensis culture grown on H2 + CO2 and H2 + CO2 + CO were analysed. Cultures grown with H2 + CO showed relative higher abundance of enzymes involved in CODH/ACS associated reactions and reactions involved in redox metabolism. Overall, the data suggests the strong reducing capacity of CO inhibits the hydrogenotrophic methanogen, making growth on CO as a sole substrate difficult for these organisms.
Project description:Syngas is a substrate for the anaerobic bioproduction of fuels and valuable chemicals. In this study, anaerobic sludge was used for microbial enrichments with synthetic syngas and acetate as main substrates. The objectives of this study were to identify microbial networks (in enrichment cultures) for the conversion of syngas to added-value products, and to isolate robust, non-fastidious carboxydotrophs. Enrichment cultures produced methane and propionate, this last one an unusual product from syngas fermentation. A bacterium closely related to Acetobacterium wieringae was identified as most prevalent (87% relative abundance) in the enrichments. Methanospirillum sp. and propionate-producing bacteria clustering within the genera Anaerotignum and Pelobacter were also found. Further on, strain JM, was isolated and was found to be 99% identical (16S rRNA gene) to A. wieringae DSM 1911T. Digital DNA-DNA hybridization (dDDH) value between the genomes of strain JM and A. wieringae was 77.1%, indicating that strain JM is a new strain of A. wieringae. Strain JM can grow on carbon monoxide (100% CO, total pressure 170 kPa) without yeast extract or formate, producing mainly acetate. Remarkably, conversion of CO by strain JM showed shorter lag phase than in cultures of A. wieringae DSM 1911T, and about four times higher amount of CO was consumed in 7 days. Genome analysis suggests that strain JM uses the Wood-Ljungdahl pathway for the conversion of one carbon compounds (CO, formate, CO2/H2). Genes encoding bifurcational enzyme complexes with similarity to the bifurcational formate dehydrogenase (Fdh) of Clostridium autoethanogenum are present, and possibly relate to the higher tolerance to CO of strain JM compared to other Acetobacterium species. A. wieringae DSM 1911T grew on CO in medium containing 1 mM formate.
Project description:Bio-augmentation could be a promising strategy to improve processes for treatment and resource recovery from wastewater. In this study, the Gram-positive bacterium Bacillus subtilis was co-cultured with the microbial communities present in wastewater samples with high concentrations of nitrate or ammonium. Glucose supplementation (1%) was used to boost biomass growth in all wastewater samples. In anaerobic conditions, the indigenous microbial community bio-augmented with B. subtilis was able to rapidly remove nitrate from wastewater. In these conditions, B. subtilis overexpressed nitrogen assimilatory and respiratory genes including NasD, NasE, NarG, NarH, and NarI, which arguably accounted for the observed boost in denitrification. Next, we attempted to use the the ammonium- and nitrate-enriched wastewater samples bio-augmented with B. subtilis in the cathodic compartment of bioelectrochemical systems (BES) operated in anaerobic condition. B. subtilis only had low relative abundance in the microbial community, but bio-augmentation promoted the growth of Clostridium butyricum and C. beijerinckii, which became the dominant species. Both bio-augmentation with B. subtilis and electrical current from the cathode in the BES promoted butyrate production during fermentation of glucose. A concentration of 3.4 g/L butyrate was reached with a combination of cathodic current and bio-augmentation in ammonium-enriched wastewater. With nitrate-enriched wastewater, the BES effectively removed nitrate reaching 3.2 mg/L after 48 h. In addition, 3.9 g/L butyrate was produced. We propose that bio-augmentation of wastewater with B. subtilis in combination with bioelectrochemical processes could both boost denitrification in nitrate-containing wastewater and enable commercial production of butyrate from carbohydrate- containing wastewater, e.g. dairy industry discharges. These results suggest that B. subtilis bio-augmentation in our BES promotes simultaneous wastewater treatment and butyrate production.
Project description:Lignocellulosic biomass is an abundant and renewable resource for biofuels and bio-based chemicals. Vanillin is one of the major phenolic inhibitors in biomass production using lignocellulose. To assess the response of Corynebacterium glutamicum to vanillin stress, a global transcriptional response analysis was performed by using microarray.
Project description:This study was conducted in order to evaluate the physiological ability for syngas conversion into propionate by a synthetic co-culture. A proteogenomics approach was used to get insight into the metabolic pathways of the conversion of CO to propionate.
Project description:One-carbon (C1) feedstocks like formate could be energetically efficient substrates for sustainable microbial production of food, fuels and chemicals. Here, we replace the native energy-inefficient Calvin-Benson-Bassham (CBB) cycle in Cupriavidus necator with the more energy-efficient reductive glycine pathway for growth on formate and CO2. In chemostats, our engineered strain reaches a 17% higher biomass yield than the wild type, or any natural formatotroph using the Calvin cycle. This demonstrates the potential of synthetic metabolism to realize sustainable, bio-based production.