Identification and characterization of lactococcal and Acetobacter strains isolated from traditional Caucasusian fermented milk

Abstract

The fermented milk, so-called "Caspian Sea Yogurt" in Japan, consists of two bacterial strains isolated from traditional Caucasusian fermented milk. In the present study, those strains were identilied and characterized. Strain FC was Gram-positive, facultatively anaerobic cocci and strain FA was Gram-negative, aerobic rods. Phylogenetic analysis based on 16S rDNA sequences showed that strain FC formed a cluster with Lactococcus lactis strains and was most closely related to L. lactis subsp. cremoris. Strain FA was included in the genus Acetobacter cluster and was most closely related to A. orientalis. The DNA G+C contents of strain FC and strain FA were 39.2 and 51.6 mol%, respectively. Biochemical tests and DNA-DNA hybridization clarified that strain FC belongs to L. lactis subsp. cremoris and strain FA belongs to A. orientalis. The culture supernatant of lactococcal strain FC inhibited the growth of L. lactis subsp. cremoris DSM 20069T and L. lactis subsp. hordniae JCM 1180T. The inhibitory activity was detected after incubation at 70°C for 60 min or 100°C for 30 min and was stable when the supernatant was adjusted to a pH ranging from 4.9 to 7.5. The antimicrobial activity was lost on treatment with proteolytic enzymes such as proteinase K, trypsin, pronase, and pepsin, although it was not affected by catalase. The gene of lactococcin B (lcnB) homolog was found in the strain FC. From the above results, the strain FC was thought to produce a bacteriocin-like substance.