Biosynthetic production of nisin Z by immobilized Lactococcus lactis IO-1

Abstract

Nisin Z, a natural nisin variant, is a lantibiotic that contains unusual amino acids. The immobilization technique was applied to improve the productivity of nisin Z, the peptide antibiotic produced by Lactococcus lactis IO-1. Both entrapment and adsorption methods of immobilization were studied with several kinds of materials in repeated fermentation. The long-term application of natural materials was limited because of the instability of the gel. Low growth rate and low productivity were obtained from the entrapment method due to the improper diffusion of nutrients through the materials. Moreover, the method to entrap the cells with photo-crosslinkable resin prepolymers caused damage to the cells. The adsorption method showed better results compared with the entrapment method. The adsorption of the cells on porous chitosan beads, Chitopearl SH-2510, gave nisin Z productivity about 1.7 times greater than the free cells. However, during the repeated cultivation, a decrease in nisin Z activity was observed. The cells adsorbed on photo-crosslinked resin gel beads, ENTG-3800, produced a greater amount of nisin Z and a lower level of lactic acid than the free cells with a good operational stability. The nisin Z production tended to increase with repeated cultivation. Continuous fermentation was introduced to improve the nisin Z productivity. Free cells showed a good productivity at the dilution rate of 0.1 h −1. However, nisin Z production was affected by cell washout at the dilution rate of 0.2 h −1. The cells adsorbed on ENTG-3800 gel beads displayed an improvement in productivity at higher dilution rates.