Three strains of anaerobic, non-spore-forming, Gram-negative coccobacilli (YIT 11816T, YIT 11817 and YIT 11818) were isolated from human faeces. On the basis of 16S rRNA gene sequence similarity, these strains were shown to belong to the family Alcaligenaceae and to be related to the type strain of Sutterella stercoricanis (94.9 %) and to Sutterella wadsworthensis WAL 7877 (94.3 %); the similarity to strains of any other species with a validly published name within the family Alcaligenaceae was less than 92 %. Biochemical data supported the affiliation of these strains to the genus Sutterella. These strains therefore represent a novel species, for which the name Sutterella parvirubra sp. nov. is proposed; the type strain is YIT 11816T (=DSM 19354T =JCM 14724T). The cells of another isolate, strain YIT 11815T, were non-spore-forming, Gram-negative, very large rods, 1x5-200 microm in size, with or without a central, subterminal or terminal swelling of 2-4 microm diameter when grown in a broth medium supplemented with glucose. Based on comparative 16S rRNA gene sequencing, this bacterium is a member of the family Acidaminococcaceae, and most closely related to Megamonas hypermegale (95.3 % similarity to the type strain). Interestingly, the 16S rRNA gene sequence of strain YIT 11815T showed 99 % similarity to sequences of uncultured colonic bacteria. A 16S rRNA gene sequence divergence value of >3 % from known cultured species suggested that isolate YIT 11815T represents a novel species, for which the name Megamonas funiformis sp. nov. is proposed; the type strain is YIT 11815T (=DSM 19343T =JCM 14723T).