Microaceticoccus formicicus gen. nov., sp. nov., an ammonia-tolerant formate-utilizing bacterium originating from a biogas process

A strictly anaerobic bacterial strain, designated as AMB_02^T, was isolated from a propionate enrichment culture obtained from a high-ammonia biogas digester. The cells were anaerobic and coccoid (0.5 µm), often appearing as diplococci or in a short chain of three to four cells. Growth was observed between 20 and 45 °C (optimum at 37-39 °C), with an initial pH of 6.5-9.0 (optimum pH 8.0-8.5), and the species tolerated up to 0.8 M NH₄Cl and 0.5 M NaCl. The major cellular fatty acids were C_{16 : 0} (31.6%), C_{14 : 0} (14.6%) and C_{18 : 0} (13.3%). AMB_02^T grew with formate, carbohydrates and aa, including asparagine, histidine, tryptone and tryptophan. Acetate was the major product formed. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain AMB_02^T was most closely related to the species <i>Citroniella saccharovorans</i> (92.5%). The genome of strain AMB_02^T was 2.5 Mb in length with a G+C content of 34.8 mol%, and 2,354 protein-coding genes were predicted. Furthermore, genes coding for the reductive glycine pathway potentially used for formate metabolism were identified. Comparative genomic analysis of AMB_02^T revealed the closest similarity to <i>C. saccharovorans</i> [21.2% digital DNA-DNA hybridization (dDDH) and 77.4% average nt identity (ANI)] and to <i>Parvimonas micra</i> (<i>2</i>4.4% dDDH and 76.9% ANI). Based on the phenotypic characteristics and phylogenetic analyses, AMB_02^T is regarded as a novel genus, <i>Microaceticoccus</i>, within the family <i>Peptoniphilaceae</i> for which the species name <i>Microaceticoccus formicicus</i> is proposed. The type strain is AMB_02^T=DSM 110248^T=JCM 39108^T.