Preliminary purification and partial characterization of a functional bacteriocin of Lacticaseibacillus paracasei Zhang and mining for its gene cluster

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Abstract
Bacteriocins produced by lactic acid bacteria have good potential for use as food biopreservatives. Lacticaseibacillus paracasei Zhang (L. paracasei Zhang) is both a food use and a probiotic bacterium. This study aimed to purify and preliminary characterize the active antibacterial metabolite of L. paracasei Zhang. The cell free supernatant of L. paracasei Zhang was collected and purified by ultrafiltration and gel filtration chromatography. The 1–3 kDa active fraction could inhibit the growth of Staphylococcus aureus but not Escherichia coli. Further antibacterial activity assays revealed its capacity in suppressing various foodborne and human opportunistic pathogens (including Staphylococcus aureus, Pseudomonas fluorescens, Pseudomonas aeruginosa, Listeria monocytogenes, and Bacillus cereus), but not fungi. The antibacterial activity showed good tolerance to heat (40℃ to 100℃), acid-base (pH 2–3 and pH 6–10), and digestions by a number of industrial and animal/human enzymes (such as trypsin, pepsin, α-amylase and protease K, except papain); these desired properties make it a suitable biopreservative to be used in harsh and complex industrial production processes. The high papain sensitivity suggested a proteinaceous/peptide nature of the bioactivity. Moreover, our genomic data mining for bacteriocin through BAGEL4 revealed an area of interest encoding a complete set of putative genes required for bacteriocin production. In conclusion, our study showed that L. paracasei Zhang can produce extracellular functional antibacterial metabolite, likely a class II bacteriocin. Our preliminary extraction and characterization of the bioactivity demonstrated that it has good potential to be used as biopreservative or agent for suppressing gastrointestinal infections.

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