Mathematical evaluation of plantaricin formation supports an auto-induced production mechanism

The production rate of a bacteriocin, produced by Lactobacillus plantarum T MW1.25 and previously named plantaricin1.25, was studied during pi-I-consta nt batch fermentations under various growth media conditions. The growth of L. plantarum and production of bacteriocin during the retardation phase we re modelled, using 11 different empirical and mechanistic approaches. The o ptimal pH for bacteriocin production was 4.5. Among the different nitrogen sources tested, yeast extract was the most important, on the basis of the f act that the maximum growth rate decreased 16% without yeast extract, and o nly 7.2% or 8.1% without meat extract or peptone respectively. However, the change of nitrogen source did not have a significant effect on bacteriocin production. The progression of plantaricin1.25 production during the retar dation phase and growth of L. plantarum TMW1.25 could be described by a str uctured model in which the bacteriocin concentration induces its own produc tion. Among those models not implementing bacteriocin induction, only the o ne with an exponential increase of bacteriocin yield per unit biomass was s uitable to describe bacteriocin production. Computer-aided evaluation of ex perimental data appears to be helpful in elucidating the relationship betwe en the growth of lactic acid bacteria and bacteriocin production.