Enhanced L-lactic acid production in Lactobacillus paracasei by exogenous proline addition based on comparative...

This study investigated cell physiological and metabolic responses of Lactobacillus paracasei to osmotic stresses. Both cellular fatty acid composition and metabolite profiling were responded by increasing unsaturated and epoxy-fatty acid proportions, as well as accumulating some specific intracellular metabolites. Simultaneously, metabolite profiling was adopted to rationally and systematically discover potential osmoprotectants. Consequently, exogenous addition of proline or aspartate was validated to be a feasible and efficacious approach to improve cell growth under hyperosmotic stress in shake flasks. Particularly, with 5-L cultivation system, L-lactic acid concentration increased from 108 to 150 g/L during the following 16-h fermentation in 2 g/L proline addition group, while it only increased from 110 to 140 g/L in no proline addition group. Moreover, glucose consumption rate with proline addition reached 3.49 g/L/h during this phase, 35.8 % higher than that with no proline addition. However, extreme high osmotic pressure would significantly limit the osmoprotection of proline, and the osmolality threshold for L. paracasei was approximately 3600 mOsm/kg. It was suggested that proline principally played a role as a compatible solute accumulated in the cell for hyperosmotic preservation. The strategies of exploiting osmotic protectant with metabolite profiling and enhancing L-lactic acid production by osmoprotectant addition would be potential to provide a new insight for other microorganisms and organic acids production.