Screening for bacteriocin-producing lactic acid bacteria from boza, a traditional cereal beverage from Bulgaria: Comparison of the bacteriocins

Lactobacillus plantarum (strains ST194BZ, ST414BZ and ST664BZ), Lactobacillus pentosus (strain ST712BZ), Lactobacillus rhamnosus (strains ST461BZ and ST462BZ) and Lactobacillus paracasei (strains ST242BZ and ST284BZ), isolated from boza, produced bacteriocins active against Lactobacillus casei, Escherichia coli, Pseudomonas aeruginosa and Enterococcus faecalis. Thus far, only a few bacteriocins with activity against Gram-negative bacteria have been reported. Complete inactivation of antimicrobial activity was observed after treatment of the bacteriocins with proteinase K, pronase, papain, chymotrypsin, trypsin, pepsin and Qiagen protease, confirming their proteinaceous nature. Treatment with catalase and α-amylase did not result in any changes of antimicrobial activity, indicating that the inhibition recorded was not hydrogen peroxide and that carbohydrate moieties were not required for antimicrobial activity. The bacteriocins remained stable after 2 h of incubation at pH values between 2.0 and 10.0, and for 120 min at 100 °C. The bacteriocins were resistant to treatment with SDS, Tween 20, urea and EDTA, but sensitive to Tween 80, Triton X-100 and Triton X-114. All bacteriocins acted bactericidal. The bacteriocins did not adhere to the surface of the producer cells. Production occurred throughout logarithmic growth, with the highest activity recorded at the end of logarithmic and during stationary growth. Based on tricine-SDS-PAGE, the bacteriocins ranged from 2.8 to 14.0 kDa in size. No plasmids were recorded, suggesting that the genes encoding the bacteriocins are located on the genomes.