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 1911 T. 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 1911 T , 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, CO 2 /H 2). 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 1911 T grew on CO in medium containing 1 mM formate.

Gas fermentation is a promising way for converting CO-rich gases to chemicals. We studied the use of synthetic co-cultures composed of carboxydotrophic and propionigenic bacteria to convert CO to propionate. So far isolated carboxydotrophs cannot directly ferment CO to propionate, and therefore this co-cultivation approach was investigated. Four distinct synthetic co-cultures were constructed, consisting of: Acetobacterium wieringae (DSM 1911T) and Pelobacter propionicus (DSM 2379T); Ac. wieringae (DSM 1911T) and Anaerotignum neopropionicum (DSM 3847T); Ac. wieringae strain JM and P. propionicus (DSM 2379T); Ac. wieringae strain JM and An. neopropionicum (DSM 3847T). Propionate was produced by all the co-cultures, with the highest titer (∼24 mM) measured in the co-culture composed of Ac. wieringae strain JM + An. neopropionicum, which also produced isovalerate (∼4 mM), butyrate (∼1 mM), and isobutyrate (0.3 mM). This co-culture was further studied using proteogenomics. As expected, enzymes involved in the Wood-Ljungdahl pathway in Ac. wieringae strain JM, which are responsible for the conversion of CO to ethanol and acetate, were detected; the proteome of An. neopropionicum confirmed the conversion of ethanol to propionate via the acrylate pathway. In addition, proteins related to amino acid metabolism and stress response were highly abundant during co-cultivation, which raises the hypothesis that amino acids are exchanged by the two microorganisms accompanied by isovalerate and isobutyrate production. This highlights the importance of explicitly looking at fortuitous microbial interactions during co-cultivation to fully understand co-cultures behavior. IMPORTANCE Syngas fermentation has great potential for the sustainable production of chemicals from wastes (via prior gasification) and flue gases containing CO/CO2. Research efforts need to be driven to expanding the product portfolio of gas fermentation, which is currently limited to mainly acetate and ethanol. This study provides the basis for a microbial process to produce propionate from CO using synthetic co-cultures composed of acetogenic and propionigenic bacteria and elucidates the metabolic pathways involved. Furthermore, based on proteomics results, we hypothesize that the two bacterial species engage in an interaction that results in amino acid exchange, which subsequently promotes isovalerate and isobutyrate production. These findings provide a new understanding of gas fermentation and a co-culturing strategy for expanding the product spectrum of microbial conversion of CO/CO2.

SummaryThe substitution of natural gas by renewable biomethane is an interesting option to reduce global carbon footprint. Syngas fermentation has potential in this context, as a diverse range of low‐biodegradable materials that can be used. In this study, anaerobic sludge acclimatized to syngas in a multi‐orifice baffled bioreactor (MOBB) was used to start enrichments with CO. The main goals were to identify the key players in CO conversion and evaluate potential interspecies metabolic interactions conferring robustness to the process. Anaerobic sludge incubated with 0.7 × 105 Pa CO produced methane and acetate. When the antibiotics vancomycin and/or erythromycin were added, no methane was produced, indicating that direct methanogenesis from CO did not occur. Acetobacterium and Sporomusa were the predominant bacterial species in CO‐converting enrichments, together with methanogens from the genera Methanobacterium and Methanospirillum. Subsequently, a highly enriched culture mainly composed of a Sporomusa sp. was obtained that could convert up to 1.7 × 105 Pa CO to hydrogen and acetate. These results attest the role of Sporomusa species in the enrichment as primary CO utilizers and show their importance for methane production as conveyers of hydrogen to methanogens present in the culture.

A syngas-degrading enrichment culture, culture T-Syn, was dominated by a bacterium closely related to Desulfofundulus australicus strain AB33 T (98% 16S rRNA gene sequence identity). Culture T-Syn could convert high CO concentrations (from pCO ≈ 34 kPa to pCO ≈ 170 kPa), both in the absence and in the presence of sulfate as external electron acceptor. The products formed from CO conversion were H 2 and acetate. With sulfate, a lower H 2 /acetate ratio was observed in the product profile, but CO conversion rates were similar to those in the absence of sulfate. The ability of D. australicus strain AB33 T to use CO was also investigated. D. australicus strain AB33 T uses up to 40% CO (pCO ≈ 68 kPa) with sulfate and up to 20% CO (pCO ≈ 34 kPa) without sulfate. Comparison of the metagenome-assembled genome (MAG) of the Desulfofundulus sp. from T-Syn culture with the genome of D. australicus strain AB33 T revealed high similarity, with an ANI value of 99% and only 32 unique genes in the genome of the Desulfofundulus sp. T-Syn. So far, only Desulfotomaculum nigrificans strain CO-1-SRB had been described to grow with CO with and without sulfate. This work further shows the carboxydotrophic potential of Desulfofundulus genus for CO conversion, both in sulfate-rich and low-sulfate environments.

Long-chain fatty acids (LCFA) are common contaminants in municipal and industrial wastewater that can be converted anaerobically to methane. A low hydrogen partial pressure is required for LCFA degradation by anaerobic bacteria, requiring the establishment of syntrophic relationships with hydrogenotrophic methanogens. However, high LCFA loads can inhibit methanogens, hindering biodegradation. Because it has been suggested that anaerobic degradation of these compounds may be enhanced by the presence of alternative electron acceptors, such as iron, we investigated the effect of sub-stoichiometric amounts of Fe(III) on oleate (C18:1 LCFA) degradation by suspended and granular methanogenic sludge. Fe(III) accelerated oleate biodegradation and hydrogenotrophic methanogenesis in the assays with suspended sludge, with H2-consuming methanogens coexisting with iron-reducing bacteria. On the other hand, acetoclastic methanogenesis was delayed by Fe(III). These effects were less evident with granular sludge, possibly due to its higher initial methanogenic activity relative to suspended sludge. Enrichments with close-to-stoichiometric amounts of Fe(III) resulted in a microbial community mainly composed of Geobacter, Syntrophomonas, and Methanobacterium genera, with relative abundances of 83–89%, 3–6%, and 0.2–10%, respectively. In these enrichments, oleate was biodegraded to acetate and coupled to iron-reduction and methane production, revealing novel microbial interactions between syntrophic LCFA-degrading bacteria, iron-reducing bacteria, and methanogens.

E.V. Kezina).Bacterial cellulose (BC) is a polymer of glucose with two qualities: the finest porosity and mechanical strength. The optimization of producer's cultivation conditions will allow to obtain a cheap, eco-friendly material with various physical-mechanical (Ph/M) and chemical properties by recycling the waste from industrial manufacturing.The BC gel-film (BCGF) was obtained by culturing Gluconacetobacter Sucrofermentans in the medium with distillery stillage (DS) and raw beet (RB). Control samples of (BCGF) were received in a standard Hestrin medium (HS). The resulting samples of (BCGF) were measured in terms of thickness, density, and tested for the strength and stretch in accordance with ASTM. The degree of crystallinity (DC) of a (BCGF) was determined by the method of X-ray diffraction. The composition of the medium greatly affects not only the release of (BC), but also the (DC) and (Ph/M) properties of (BCGF). The output of BC and the thickness of the films with (DS) was more than with (HS) and with (RB). (DC) and the strength of (BC) obtained in (HS) and in (RB) was higher than in (DS). The stretch of the films obtained in the (DS) was higher than in other medium.

Glycerol-rich waste streams produced by the biodiesel, bioethanol and oleochemical industries can be treated and valorized by anaerobic microbial communities to produce methane. As current knowledge of the microorganisms involved in thermophilic glycerol conversion to methane is scarce, thermophilic glycerol-degrading methanogenic communities were enriched. A co-culture of Thermoanaerobacter and Methanothermobacter species was obtained, pointing to a non-obligately syntrophic glycerol degradation. This hypothesis was further studied by incubating Thermoanaerobacter brockii subsp. finnii and T. wiegelii with glycerol (10 mM) in pure culture and with different hydrogenotrophic methanogens. The presence of the methanogen accelerated glycerol fermentation by the two Thermoanaerobacter strains up to 3.3 mM day À1 , corresponding to 12 times higher volumetric glycerol depletion rates in the methanogenic co-cultures than in the pure bacterial cultures. The catabolic pathways of glycerol conversion were identified by genome analysis of the two Thermoanaerobacter strains. NADH and reduced ferredoxin formed in the pathway are linked to proton reduction, which becomes thermodynamically favourable when the hydrogen partial pressure is kept low by the hydrogenotrophic methanogenic partner.