Inducing the Production of the Bacteriocin Paenibacillin by Paenibacillus Polymyxa Through Application of Environmental Stresses with Relevance to Milk Bio-Preservation.

Food processors are keenly interested in natural alternatives to currently used chemical preservatives. Although bacteriocins of beneficial bacteria are one of the promising alternatives, low productivity of bacteriocin producers has been limiting the application of these agents in food processing. The present study was designed to examine the possibility of inducing the production of paenibacillin, a bacteriocin produced by Paenibacillus polymyxa OSY-DF, by exposing this organism to environmental stresses. Cold stress (15 degrees C for 105 min) caused 2- to 4-fold increase in the antibacterial and specific antibacterial activities of bioreaction's cell-free filtrate against Listeria innocua and Bacillus subtilis. Paenibacillin production increased when the organism was exposed during incubation to pH 6.0. Presence of 1% NaCl in the growth medium, application of oxidative stress by exposure to 3 ppm H2O2, and adjusting aeration to a relatively low rate were also found to induce the expression of paenibacillin but to a limited degree, when compared to the effect of cold stress. Exposure to pH 6 increased the transcription of the paenibacillin structural gene, paeA, whereas no significant change was noticed for the same gene under cold stress. Paenibacillin, produced in sufficient amounts under cold stress, was tested as a potential preservative to control the sporeforming bacterium, B. subtilis, in milk. The initial population of B. subtilis of similar to 7 log(10) CFU/ml decreased to an undetectable level (<= 1 log(10) CFU/ml) within 24 h of incubation of treated milk held at 37 degrees C. Similarly, paenibacillin was active against L. innocua in milk; the treatment caused 5-log decrease in the organism's population after 7 days of incubation. Taken together, these results demonstrated increased expression of paenibacillin by exposure to selected environmental stresses, particularly cold stress, and that paenibacillin seems promising in the biopreservation of milk and potentially milk products.