Novel Bacteriocin-Producing Lactobacillus Strains from Fermented Foods of the South South Geopolitical Zone: Isolation, Characterisation, and Biopreservation Applications

Bacteriocins are ribosomally synthesised antimicrobial peptides produced by lactic acid bacteria that inhibit the growth of closely related bacteria, including major foodborne pathogens. The South South geopolitical zone of Nigeria, with its rich diversity of fermented food products, represents an underexplored ecological reservoir for novel bacteriocin-producing strains with biotechnological potential. This thesis reports the comprehensive isolation, genetic and biochemical characterisation, and food biopreservation application of novel bacteriocin-producing Lactobacillus strains from fermented foods of the South South geopolitical zone, with primary focus on ogiri-okpei (fermented Pentaclethra macrophylla), palm wine, and fresh palm sap from Rivers, Cross River, and Delta states. A screening collection of 340 lactic acid bacteria isolates was established. Bacteriocin producers were identified by spot-on-lawn and well diffusion assays. Promising producers were characterised by whole-genome sequencing and bioinformatic mining of bacteriocin biosynthetic gene clusters using antiSMASH and BAGEL4. Biochemical characterisation of purified bacteriocins included proteinase sensitivity, temperature and pH stability, molecular weight determination by tricine-SDS-PAGE, and minimum inhibitory concentration against indicator strains including Listeria monocytogenes ATCC 7644 and Staphylococcus aureus ATCC 25923. Biopreservation efficacy was evaluated in smoked fish, fresh-cut watermelon, and a probiotic yoghurt model system. Results identified five novel Lactobacillus strains producing bacteriocins with novel gene cluster architectures not previously reported. Two bacteriocins demonstrated exceptional thermal stability (active at 100 degrees Celsius for 30 minutes) and broad inhibitory spectrum. Keywords: bacteriocin, Lactobacillus, fermented foods, biopreservation, South South Nigeria.