Antimicrobial Substance Produced by Pseudomonas aeruginosa Isolated from Slaughterhouse Sediment: Physicochemical Characterization, Purification, and Identification

Purification and characterization of a bacteriocin produced by the probiotic Lactiplantibacillus plantarum subsp. argentoratensis strain I1B

This study is aimed to characterize a broad-spectrum bacteriocin produced by Lactiplantibacillus plantarum subsp. argentoratensis strain I1B of fermented food origin and also to evaluate the in vitro probiotic properties of this strain. Cell supernatant of this strain showed broad-spectrum antibacterial activity against five prominent foodborne pathogens viz. Salmonella typhi 950, Escherichia coli 728, Yersinia enterocolitica 861, Listeria monocytogenes 657, and Klebsiella pneumoniae 618 with the strongest activity against the S. typhi 950. Cell supernatant also exhibited stability to proteolytic enzyme treatment, pH, and temperature. Optimum bacteriocin production was at 20-24 h of incubation in MRS broth at 37 °C with pH 6.0. The bacteriocin activity was retained in the 70% ammonium sulfate precipitate fraction, which was further purified using gel filtration chromatography (Sephadex G25 column) to the level of a single band on the SDS-PAGE and the activity was confirmed by zymogram. The molecular mass of the bacteriocin was found to be 22,199 Daltons. The pure molecule was identified using LC-MS/MS and was found to be an Adherence Protein with a sequence of chitin-binding domain consisting of 201 amino acid residues. The isolated strain exhibited potential probiotic activity within the established regulations and did not raise any possible safety concerns. This work reports a potent bacteriocin produced by a listed probiotic organism with latent postbiotic activity which could be used as a potential biopreservatives.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-025-04279-5.

Optimisation of cultivation conditions for Bacillus velezensis G7 from mangrove plants and exploration of potential bacteriocins

Introduction

Bacteriocin P7 was extracted from the cell-free supernatant (CFS) of Bacillus velezensis G7, which is a strain isolated from mangrove plants.

Methods

In this study, the culture conditions of B. velezensis G7 were optimised using an orthogonal test. The (CFS) was subsequently purified by using TA-GF75 gel chromatography, Tiderose Q HP anion chromatography and reversed-phase high-performance liquid chromatography (RP-HPLC). Finally, the bacteriocin was identified by using LC-MS/MS.

Results and discussion

The optimal culture conditions for B. velezensis G7 are 4.5 g/100 mL glucose, 1.5 g/100 mL yeast, and 1.2 g/100 mL MgSO4·7H2O. The stability of the CFS is affected by several factors, including heat, UV treatment and different storage conditions. High temperatures and long UV irradiation treatments significantly reduce the stability of CFS, which is more sensitive to strong acids, bases and enzymatic degradation. The minimum inhibitory concentration (MIC) of purified bacteriocin P7 against S. aureus was determined to be 30.352 μg/mL. On the basis of the results of the haemolytic activity assay, it was concluded that the use of bacteriocin P7 at concentrations equal to or below the 2 × MIC is safe. The addition of organic solvents and inorganic salts did not affect the bacteriocin P7, while the incorporation of SDS could enhance its antimicrobial efficacy. The bacteriocin was subjected to analysis by LC-MS/MS, which revealed that it was similar to the class I bacteriocin amyloliquecidin GF610. The findings of the present study indicate that the endophytic B. velezensis G7 from mangrove plant can produce bacteriocins, thereby providing a reference point for the expansion of novel bacteriocin sources.

Antibacterial Activity and Cytotoxicity of the Novel Bacteriocin Pkmh

Bacteriocins are a class of proteins produced by bacteria that are toxic to other bacteria. These bacteriocins play a role in bacterial competition by helping to inhibit potential competitors. In this study, we isolated and purified a novel bacteriocin Pkmh, different from the previously reported bacteriocin PA166, from Pseudomonas sp. strain 166 by ammonium sulfate precipitation, dialysis membrane method, ion exchange chromatography, and gel filtration chromatography. SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) revealed that the molecular weight of Pkmh is approximately 35 kDa. Pkmh exhibited potent antimicrobial activity against bovine Mannheimia haemolytica (M. haemolytica) with low cytotoxicity, and lower hemolytic activity was observed. In addition, Pkmh retained antimicrobial activity at different pH ranges (2-10) and temperature conditions (40, 60, 80, 100 °C). Our analysis of its antimicrobial mechanism showed that Pkmh acts on bacterial cell membranes, increasing their permeability and leading to cell membrane rupture and death. In conclusion, Pkmh exhibited low hemolytic activity, low toxicity, and potent antibacterial effects, suggesting its potential as a promising candidate for clinical therapeutic drugs.