Nisin-producing Lactococcus lactis subsp. lactis 2MT isolated from freshwater Nile tilapia in Cameroon: Bacteriocin screening, characterization, and optimization in a low-cost medium

This work was aimed to isolate bacteriocin-producing lactic acid bacteria (LAB) from freshwater fish in Cameroon, characterize the bacteriocin and investigate its production as well as growth optimization in low-cost media. From the 144 isolates obtained, two showed the ability to produce bacteriocin-like inhibitory substances. Isolate 2 MT, selected for its high bacteriocin production capacity was identified as Lactococcus lactic subsp. lactis using 16S rDNA sequencing. The bacteriocin expressed high stability to heat, pH and chemical agents. Lactococcus lactic subsp. lactic 2 MT harbored the gene for the production of nisin Z, and the bacteriocin molecular mass was estimated at 4.10 kDa. This bacteriocin also exhibited a wide range of antimicrobial activity against spoilage and pathogenic Gram-positive and Gram-negative bacteria. The fish processing byproducts-based formulated medium SP1M showed the significantly highest bacteriocin production capacity. Using Doehlert design, a sugar cane molasses concentration of 42.72 g/l, a temperature of 28.40 degrees C, and an incubation time of 17.05 h were recorded as the optimum conditions for bacteriocin production. The optimization led to a 4.5-fold increase in nisin, compared with the non-optimized conditions, and a 9-fold increase when compared with non-optimized MRS broth.