Masaru Sakamoto

Plasmid-associated bacteriocin production by and immunity of Lactobacillus acidophilus TK8912

Lactobacillus acidophilus TK8912 produces an antibacterial substance, designated acidocin 8912, which is active against strains of Lactobacillus and Lactococcus. Of all conditions tested, the production of acidocin 8912 was maximum at 30°C in MRS broth. Acidocin 8912 was stable to heat treatment (120°C for 20min), but completely inactivated by protease treatment. Curing a plasmid pLA103 resulted in the loss of both acidocin 8912 production (Acd(+)) and host immunity (Acd(r)). A plasmid-cured strain, TK1-4 (Acd(-) Acd(8)), was transformed to Acd(+)Acd(r) with the pLA103 plasmid. These results provided the first direct evidence in lactobacilli for involvement of this plasmid in bacteriocin production and immunity.

Transformation of Lactobacillus acidophilus TK8912 by electroporation with pULA105E plasmid

An efficient method for the transformation of Lactobacillus acidophilus TK8912 by electroporation is presented. The plasmid vector pULA105E was constructed by joining a cryptic plasmid, pLA 105, from L. acidophilus TK8912, the Escherichia coli vector pUC19, and the erythromycin resistance gene of the Streptococcus-Escherichia coli shuttle vector pVA838. Plasmid pULA105E was introduced into L. acidophilus TK1-5 at a frequency of 7.4 × 106 transformants per μg of plasmid DNA under optimized conditions. Other Lactobacillus strains, L. casei JCM 1053 and TK9008, were also transformed with pULA105E.

Inhibition of hiochi-bacteria by nisin

Abstract Hiochi-bacteria, composed of typical culture strains and newly isolated strains, were investigated for their sensitivity to nisin, which was produced by Lactococcus lactis subsp. lactis . Most of the strains tested showed sensitivity to nisin. This antibacterial action was inactivated by sake ingredients such as protesase, whereas the preservative effect of nisin was observed in heat-treated or ultrafiltered sake. These results suggest that the application of nisin in sake brewing may be of value in controlling biochi-bacteria.