Submitted to: Journal of Applied Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/28/2009
Publication Date: 2/2/2010
Citation: Renye Jr, J.A., Somkuti, G.A. 2010. Nisin-induced Expression of Pediocin in Dairy Lactic Acid Bacteria. Journal of Applied Microbiology. 108:2142-2151. Interpretive Summary: Contamination of dairy products with foodborne pathogens is a major concern, and there is a constant need to develop new techniques to prevent their growth. Fortunately, some lactic acid bacteria (LAB) considered safe for human consumption have been shown to produce peptides, short proteins called bacteriocins, which inhibit the growth of other bacteria including foodborne pathogens. Some LAB are unable to grow in milk because they cannot use lactose, but dairy LAB can be made to produce bacteriocins as natural preservatives in fermented dairy products. In this study, we developed a way to introduce a bacteriocin, which inhibits the growth of Listeria, into dairy LAB such as Streptococcus thermophilus, Lactococcus lactis and Lactobacillus casei. The presence of nisin, a food grade bacteriocin approved for human consumption, was required for optimum bacteriocin production. Bacteriocin expression was shown to effectively inhibit the growth of the food pathogen Listeria monocytogenes. These results demonstrate that it is possible to make LAB that will produce natural biopreservatives to protect dairy products from bacterial contamination.
Technical Abstract: To test if a single vector, nisin-controlled expression (NICE) system could be used to regulate expression of the pediocin operon in Streptococcus thermophilus, Lactococcus lactis subsp. lactis and Lactobacillus casei, the intact pediocin operon was cloned into pMSP3535 immediately down stream of the nisA promoter (PnisA). The resulting vector, pRSNPed, was electrotransformed into Strep. thermophilus ST128, L. lactis subsp. lactis ML3 and Lact. casei C2. Presence of the intact vector was confirmed by PCR, resulting in the amplification of a 0.8 kb DNA fragment, and inhibition zones were observed for all LAB transformants following induction with 50 ng ml-1 nisin when Listeria monocytogenes Scott A was used as the target bacterium. Using L monocytogenes NR30 as target, the L. lactis transformants produced hazy zones of inhibition, while the Lact. casei transformants produced clear zones of inhibition. Zones of inhibition were not observed when the Strep. thermophilus transformants were tested against NR30. This is the first time that the NICE system has been used to express the intact pediocin operon in these LAB hosts. This system could allow for the in situ production of pediocin in fermented dairy foods supplemented with nisin in order to prevent listeria contamination.