Genetic Characterization of Enterococcus Faecalis N1-33 Bacteriocin and Obtained of the Mutant Strain that Produce Many Bacteriocin by Novobiocin Agent Effect, its Merit as A Food Preservative in Steamed Rice Model

摘要

Enterococcus faecalis strain N1-33 produces a peptide that shows bacteriocin activity, enterocin MR10A (EntMR10A). We cloned and sequenced the structural gene of the EntMR10A locus (entMR10A), and the peripheral region of entMR10A was analyzed. Inverted repeat-like structure was found for at both ends of entMR10A and so that it suggested entMR10A of strain N1-33 could be formed from an insertion sequence. Attempting to eliminate the plasmid from strain N1-33 using the plasmid-curing agent novobiocin was obtained the mutant strain of N1-33 which seemed to overproduction of bacteriocin than the original strain, termed N41-51. The number of originated bacteriocin structural genes detected by real-time PCR showed that its level of the strain N41-51 was about twofold higher than that of N1-33, and correspondingly appeared to produce about twofold more bacteriocin compared with the original strain in these culture broth, respectively. This difference as a food preservative potential was examined whether it proves the same result in the actual food systems, by using steamed rice. The culture supernatant of strain N41-51 has confirmed to inhibit the growth of Bacillus cereus by significantly less amount added to steamed rice than that of N1-33.