Acidaminococcus faecalis sp. nov., an indole-producing bacterium isolated from the feces of an adult.

A Gram-negative, coccoid, catalase-negative, and non-motile bacterial strain, designated DS4831T, was isolated from the feces of an adult in the Republic of Korea. The morphological and growth characteristics of this strain were consistent with those of the genus Acidaminococcus. Colonies of strain DS4831T grown on Gifu Anaerobic Medium agar were white, smooth, opaque, and circular with an average diameter of 0.5mm. Optimal growth occurred at 37 °C and pH 7.0, and the strain was able to grow in the presence of NaCl concentrations ranging from 0 to 4.5% (w/v), but not above this range. Based on 16S rRNA gene sequence analysis, Strain DS4831T showed the highest sequence similarity 98.38% to Acidaminococcus fermentans KCTC 15585T, followed by Acidaminococcus hominis KCTC 25346T (96.4%) and Acidaminococcus intestini KCTC 15529T (95.54%). Average nucleotide identity value between strain DS4831T and Acidaminococcus fermentans KCTC 15585T was 85.79%, and digital DNA-DNA hybridization value was 31.1%, both of which are well below the accepted species delineation thresholds of 95-96% and 70%, respectively. Strain DS4831T, utilizes glutamic acids as its primary energy source and produces acetic acid and butyric acid. Notably, it also possesses a distinctive trait of indole production through tryptophanase activity. Strain DS4831T consists of 2,445,881 bp with a G+C content of 54.02 mol%. The major cellular fatty acids were C12:0 (13.18%), C16:1 (12.27%), and C18:1 cis-9 (20.31%). Based on phenotypic, chemotaxonomic, and phylogenetic analyses, strain DS4831T (=KCTC 25843T =JCM37388T) represents a novel species within the genus Acidaminococcus, for which the name Acidaminococcus faecalis sp. nov. is proposed.