Enrichment of Anaerobic Syngas-Converting Communities and Isolation of a Novel Carboxydotrophic Acetobacterium wieringae Strain JM

Abstract

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.

Propionate Production from Carbon Monoxide by Synthetic Cocultures of Acetobacterium wieringae and Propionigenic Bacteria

“…on May 30, 2021 by guest http://aem.asm.org/ Downloaded from Previously, we described an enrichment culture that produced acetate and propionate from CO (15). This culture was predominantly composed of microorganisms affiliated with Acetobacterium wieringae (87 % relative abundance), and propionigenic bacteria closely related to Pelobacter propionicus and Anaerotignum neopropionicum (1 and 2 %, respectively) (15).…”

“…Ac. wieringae strain JM was subsequently isolated from this enrichment (15). When grown solely on CO, strain JM produced acetate and ethanol, but not propionate.…”

“…Propionate has several industrial applications, e.g., as an antifungal agent in food and feed, and as a building block to produce plastics and herbicides (16). Its biological production from C1 compounds is only reported in open mixed cultures, where a mixture of volatile fatty-acids is obtained (15). Approaches for microbial selective propionate production commonly involve Propionibacterium species, which can use sugars, glycerol, and lactate as substrates (16), but not from CO or products from CO fermentation.…”

Defining Genomic and Predicted Metabolic Features of the Acetobacterium Genus

“…Acetobacterium woodii encodes only a single Rnf complex (21), but Acetobacterium wieringae and Acetobacterium sp. MES1 were found to encode two (14,63,64). The function of the second Rnf complex in Acetobacterium is unknown, but closer examination of the remaining Acetobacterium genomes revealed that the majority of Acetobacterium genomes encode a second rnfCDGEAB cluster (Data Set S2).…”

“…UBA6819 were the only strains to encode a complete AdhE with 87% sequence identity to A. woodii (Data Set S2). Despite the lack of AdhE in the other species of Acetobacterium, species like A. wieringae are capable of growth on ethanol (Table 3) (64,71,(75)(76)(77). It is likely that A. wieringae and the other Acetobacterium strains that do not encode the A. woodii-type bifunctional acetaldehyde-CoA/alcohol dehydrogenase employ an alternative pathway for ethanol oxidation.…”