Comparative genomics identifies species-specific T6P pathway in Lb. casei group. β-Galactosidase activity was undetectable in Lb. casei group via ONPG assay. Lb. casei group catabolize lactose with little galactose accumulation in the media. Lb. casei group strains utilize galactose efficiently. T6P pathway is a major contributor for lactose/galactose catabolism in Lb. casei group.