The bacteriocins of lactic acid bacteria: Production, purification, genetic control and application

Bacteriocins of food grade lactic acid bacteria have potential for use as food biopreservatives. For economical use, the bacteriocins have to be produced in large amounts. The influence of several factors on production of nisin by Lactococcus lactis, pediocin AcH by Pediococcus acidilactici, leuconocin Lcm 1 by Leuconostoc carnosum Lm 1 and sakacin A by Lactobacillus sake Lb 706 was studied. Production of a bacteriocin in a simple liquid medium can be increased by growing the cells at optimum pH and supplementing the medium with species specific nutrients. Conditions that provide high cell density favor high bacteriocin production. The production of bacteriocins in an economical dairy-based medium was also studied. A medium containing 1% nonfat-dry-milk, 2% whey and supplemented with 0.2% lactase facilitated high bacteriocin production at optimal pH.; A novel and economical large scale purification method was developed for bacteriocins produced by four genera of LAB. The method was based on the observation that 93% to 100% of the bacteriocins produced can be adsorbed on the cell wall surface of the producing cells at pH 6 to 7, and released from the cell surface at pH below 2. Thus, by adjusting the pH of the environment bacteriocins can be adsorbed on and released from the cells and concentrated.; Nucleotide sequence analysis of the structural gene from P.acidilactici RS2, reported to produce pediocin with different amino acid sequence than pediocin AcH, revealed it to be identical to that in strain LB 42-923. The four gene cluster encoding pediocin production in plasmid pSMB74, was cloned in a shuttle vector pHPS9 and the recombinant plasmid(pMBR1.0) was transformed in E.coli JM109. Gene-deletion analysis revealed that only pap A and pap D are required for production of active pediocin AcH in E.coli JM109. Expression of these four genes in the mini-cells of E.coli {dollar}chi{dollar}925 suggested that a polar effect during transcription of the genes as revealed by the production of proteins with Mr 6.5kDa(pap A), 11.5kDa(pap B), 19kDa (pap C) and about 80 kda(pap D).; Leuconostocs were predominant spoilage bacteria in the vacuum-packaged commercial meat products. Many of these leuconostoc isolates produced bacteriocins and became predominantly by inhibiting growth of other bacteria. The isolates were sensitive to nisin. Thus, either by adding nisin to the products or by incorporating nisin-producing live cells in the package, the leuconostocs can be controlled.