A strictly anaerobic, Gram-stain-negative, non-spore-forming, motile bacterium, designated strain FSRU B0405(T), was isolated from a commercial pickle spoilage tank and characterized by biochemical, physiological and molecular biological methods. Analyses of the 16S rRNA gene sequence of strain FSRU B0405(T) showed affiliation to the class Negativicutes in the phylum Firmicutes, with the closest relatives being the type strains of Pectinatus haikarae (96 %) and Pectinatus brassicae (95 %). In maximum-likelihood and neighbour-joining phylogenetic trees, strain FSRU B0405(T) clustered definitively (in 100 % of bootstrapped trees) within the genus Pectinatus, but not specifically with any characterized species within this genus. Strain FSRU B0405(T) was a slightly curved rod, varying from 3 to 30 µm in length, motile with a distinctive X-wise movement, having flagella only on the concave side of the cell. The isolate produced acetate and propionate from fructose and glucose as major metabolites similar to type strains of species of the genus Pectinatus. The major fatty acids were C11 : 0, C13 : 0, C15 : 0, C13 : 0 3-OH, C17 : 1 and C18 : 1ω11t. Strain FSRU B0405(T) differed from the pickle wastewater strain, Pectinatus brassicae TY(T), due to its lack of susceptibility to vancomycin, acetoin production, growth temperature range, acid production from adonitol, erythritol, glycerol, inositol, lactose, maltose, mannose, ribose, salicin, sorbitol, trehalose and xylitol and lack of hydrolysis of milk. Strain FSRU B0405(T) could be differentiated from other species of the genus Pectinatus both phenotypically and genetically. The results indicate that strain FSRU B0405(T) represents a novel species of the genus Pectinatus, for which the name Pectinatus sottacetonis sp. nov. is proposed. The type strain is FSRU B0405(T) ( = ATCC BAA-2501(T) = VTT E-113163(T)). An emended description of the genus Pectinatus is also provided.