Objective:Lactobacillus plantarum RX-8 was isolated from Chinese traditional pickles and shown to produce plantaricin EF,a genetically characterized inducible class IIb bacteriocin.It has broad spectrum antibacterial ability,good processing application characteristics and great potential application as a natural food biological preservative.However,plantaricin EF encounter various limits both in industrial fermentation and application because of its low synthesis.This work aimed at showing the effect of exogenous microorganisms act as an environmental stimulus activating plantaricin EF production by Lactobacillus plantarum RX-8.Method:Based on the existing conventional pure culture conditions and the main influencing factors of bacteriocin production by strain RX-8,two pure culture model systems with low and no bacteriocin production were established.Aliquots of the 16 strains from different fermented food sources were added to fresh MRS broth containing Ca.108 CFU/mL of an overnight culture of Lactobacillus plantarum RX-8.By comparing the bacteriocin antibacterial activity in co-culture and pure culture,the best co-culture induced strains and their conditions were screened and determined.To study the specific types of induction,the inducing activity of different treatments with living-cells and supernatants were tested.Results:When Bacillus subtilis BS-15 from grain vinegar was co-cultured with the strain RX-8,it showed significant induction ability (P<0.01).The best bacteriocin production was induced by co-cultivation as follows:the optimal inoculation ratio of Bacillus subtilis BS-15 and Lactobacillus plantarum RX-8 was 10:1,and the inoculation concentration was 108 CFU/mL and 107 CFU/mL respectively.It was speculated that the induction was caused by the protein substances secreted by Bacillus subtilis BS-15.Conclusion:Taken together,the results suggest that the presence of specific microorganisms act as environmental stimulus activating plantaricin EF production.Microbial co-cultivation can be used as an important technical means to increase the production of lactic acid bacteria.