Two indigo-reducing alkaliphilic strains, designated strain C40(T) and strain N214, were isolated from a fermented Polygonum Indigo (Polygonum tinctorium Lour.) liquor sample aged for 10 months and obtained from Date City, Hokkaido, Japan. 16S rRNA gene sequence phylogeny suggested that strains C40(T) and N214 were members of the genus Amphibacillus with the closest relative being Amphibacillus xylanus JCM 7361(T) (97.5 % 16S rRNA gene sequence similarity with strain C40(T)), which is the only strain having a 16S rRNA gene sequence similarity higher than 97 % with strain C40(T). Cells of strain C40(T) were Gram-stain-positive, facultatively anaerobic, straight rods that were motile by means of peritrichous flagella. The strains grew between 17 and 39 °C (optimum, 35 °C) and in the pH range of 9.0-12.0. No isoprenoid quinone was detected and the DNA G+C content was 37.5-37.7 mol%. The whole-cell fatty acid profile mainly consisted of iso-C(15 : 0) and anteiso-C(15 : 0). DNA-DNA hybridization of strain C40(T) with Amphibacillus xylanus JCM 7361(T) revealed a DNA-DNA relatedness value of 10±3 %. Owing to the differences in phenotypic characteristics and phylogenetic analyses based on 16S rRNA gene sequences, as well as DNA-DNA relatedness data from reported species of the genus Amphibacillus, the isolates merit classification as a novel species in the genus Amphibacillus, for which the name Amphibacillus indicireducens sp. nov. is proposed. The type strain is C40(T) ( = JCM 17250(T) = NCIMB 14686(T)). An additional strain of the species is N214. An emended description of the genus Amphibacillus is provided.