Antibacterial Peptide Secreted by Pediococcus acidilactici Enables Efficient Cellulosic Open L-Lactic Acid Fermentation

Maintaining aseptic conditions is one of the major cost factors in industrial fermentation. Here, we have demonstrated an open fermentation method for producing cellulosic L-lactic acid by Pediococcus acidilactici, which is also capable of secreting an antibacterial peptide to control potential microbial contamination. The peptide secreted by P. acidilactici TY112 was isolated and its molecular weight was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). P. acidilactici TY112 was applied to an open L-lactic acid fermentation without sterilizing reactors, medium and supporting facilities. No contamination was observed and high L-lactic acid fermentation performances were obtained during open fermentation in synthetic medium and corn stover hydrolysates, both in separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) modes. The open SSF at 30% (w/w) solids loading reached 97.3 g/L of L-lactic acid with a productivity of 1.5 g/(L.h) and yield of 69.4%, which were comparable to the conventional SSF with sterilization. The antibacterial peptide secreted by P. acidilactici enabled a successful and more cost-effective open L-lactic acid fermentation method, without energy-consuming sterilization protocols. Potentially, the open fermentation concept presented herein can be applied to other fermentative processes in the future, by expressing appropriate antibacterial peptides in the desired microbial strains.