Identification and characterisation of thuricin 17-like bacteriocins produced by Bacillus thuringiensis and Bacillus cereus isolates

Introduction

Bacillus species are bacteria with a broad application profile in food production. They are used as starter cultures in modern biotechnological processes and in traditionally fermented products. They are capable of producing bacteriocins, ribosomally synthesised peptides with high antibacterial activity. Bacteriocins do not affect the sensory properties of foods or the composition of the human gut microbiota, as they are degraded by proteases in the gastrointestinal tract. The Bacillus cereus group consists of several genetically closely related species, such as B. cereus sensu stricto, B. anthracis, or B. thuringiensis. The latter has recently come to the fore for its ability to produce bacteriocins, in particular thuricins (thuricin 17 and thurincin H). However, their properties have not yet been fully characterised.

Goals

The aim of the present study was the identification and characterization of bacteriocins from different B. cereus and B. thuringiensis isolates.

Materials & Methods

Supernatants of various Bacillus strains isolated from foods were tested by the agar well diffusion method for their antimicrobial activity towards Listeria monocytogenes. To determine the molecular weight of the bacteriocins, SDS-PAGE and silver staining were performed. Finally, the sensitivity of the bacteriocins to temperature and enzymes such as proteinase K, pronase E, trypsin, lipase and amylase was evaluated.

Results

Six Bacillus isolates showed antibacterial activity towards L. monocytogenes. The molecular weight of the corresponding bacteriocins was approx. 6 kDa. Antimicrobial activity was eliminated by proteinase K and pronase E. No decrease in activity was observed when samples were treated with trypsin, lipase, amylase, or temperatures up to 65 °C. Examination of the putative gene clusters in the genomes of the tested Bacillus isolates revealed high similarity of the peptide sequences to thurincin H and thuricin 17 as well as a conserved motif specific to these bacteriocins.

Summary

We report 6 bacteriocins from B. cereus and B. thuringiensis isolates with high similarity to thuricin 17. Confirmation via MALDI-ToF-MS is ongoing.