Development of a culture strategy to produce a bacteriocin type substance utilizing a strain of Enterococcus mundtii

Abstract

Lactic acid bacteria produce a variety of bacteriocins, peptide molecules that act inhibiting growth of Gram-positive bacteria. The strain of Enterococcus mundtti used in this work was isolated at a salmon processing factory located southern Chile. Growing in MRS medium it exhibits a high production capacity of a bacteriocin type substance (BTS) very active against Listeria monocytogenes. Previous studies usingMRSmediumshown that BTS is produced growth associated obtaining a maximum volumetric productivity of 3.74*108 (AU/L*h) at pH 6.2 and 30 ◦C. The objective of this work was to develop a fermentation strategy to maximize the volumetric productivity of BTS using MRS medium. Experimentswere conductedbatchwise ina2Lbioreactorusing MRS medium, at 30 ◦C and 1 vvm. The agitator was a Rushton type turbine operated at 300 rpm. Initially four fermentations were run intending to evaluate the effect of aeration and pH control policy on BTS productivity. First and second runs were aerated and pH controlled automatically adding KOH in one case and using phosphate buffer in the other. Third and fourth runs were non-aerated and the same pH policy as before respectively. The condition using aeration and phosphate buffer gave the best results of BTS volumetric productivity equal to 1.87109 (AU/Lh) and a product yield of 6.8109 (UA/gcel). It was observed that high BTS production was stimulated by pH fall from 6.2 to 4.8 during growth phase. These results allowed designing a fermentation strategy consisting of a two stage batch operation. The first stage was aerated and pH controlled automatically and the second also was aerated but without pH control. BTS volumetric productivity was 2.171010 (AU/Lh) and product yield was 5.21010 (UA/gcel). By using this strategy volumetric productivity was increased by a factor of 11.6, using in both cases the sameMRS culture medium.