Growth of the bacteriocin-producing Lactobacillus sakei strain CTC 494 in MRS broth is strongly reduced due to nutrient exhaustion: a nutrient depletion model for the growth of lactic acid bacteria

Although commercial MRS broth has been designed to allow excellent growth o f lactobacilli, most of these bacteria are still subjected to a self-inhibi ting process. The most likely explanation is the accumulation of lactic aci d or other toxic end products and the depletion of nutrients. In this study , the self-inhibition of Lactobacillus sakei CTC 494 was analyzed in a kine tic way, and a nutrient depletion model was set up to describe the growth i nhibition process. This simple model has considerable advantages compared t o commonly used descriptive models such as the logistic growth equation. It offers a better fit and a more realistic description of the growth data by taking into account both growth inhibition due to lactic acid production a nd changes in growth rates due to nutrient depletion. Depending on the ferm entation conditions, in MRS broth there appears to be a strong decrease of the specific growth rate over time. Some undefined compounds present in the complex nitrogen source of MRS broth appear to be of crucial importance be cause of their limited availability. Moreover, nutrient availability affect s bacteriocin production through its effect on cell growth as well as on th e bacteriocin production per cell. A plateau value for the bacteriocin prod uction by L. sakei CTC 494 was observed.