Bacteriocin thuricin-S

We report the isolation and characterization of a new bacteriocin, thuricin S, produced by the Bacillus thuringiensis subsp. entomocidus HD198 strain. This antibacterial activity is sensitive to proteinase K, is heat-stable, and is stable at a variety of pH values (3-10.5). The monoisotopic mass of thuricin S purified by high performance liquid chromatography, as determined with mass spectrometry ESI-TOF-MS, is 3137.61 Da. Edman sequencing and NanoESI-MS/MS experiments provided the sequence of the 18 N-terminal amino acids. Interestingly, thuricin S has the same N-terminal sequence (DWTXWSXL) as bacthuricin F4 and thuricin 17, produced by B. thuringiensis strains BUPM4 and NEB17, respectively, and could therefore be classified as a new subclass IId bacteriocin.

A wide range of prokaryotes produce and excrete bacteriocins (proteins with antimicrobial activity) to reduce competition from closely related strains. Application of bacteriocins is of great importance in food industries, while little research has been focused on the agricultural potential of bacteriocins. A number of bacteriocin producing bacteria are members of the phytomicrobiome, and some strains are plant growth promoting rhizobacteria (PGPR). Thuricin 17 is a single small peptide with a molecular weight of 3.162 kDa, a subclass IId bacteriocin produced by Bacillus thuringiensis NEB17, isolated from soybean nodules. It is either cidal or static to a wide range of prokaryotes. In this way, it removes key competition from the niche space of the producer organism. B. thuringiensis NEB17 was isolated from soybean root nodules, and thus is a member of the phytomicrobiome. Interestingly, thuricin 17 is not active against a wide range of rhizobial strains involved in symbiotic nitrogen fixation with legumes or against other PGPR. In addition, it stimulates plant growth, particularly in the presence of abiotic stresses. The stresses it assists with include key ones associated with climate change (drought, high temperature, and soil salinity). Hence, in the presence of stress, it increases the size of the overall niche space, within plant roots, for B. thuringiensis NEB17. Through its anti-microbial activity, it could also enhance plant growth via control of specific plant pathogens. None of the isolated bacteriocins have been examined as broadly as thuricin 17 on plant growth promotion. Thus, this review focuses on the effect of thuricin 17 as a microbe to plant signal that assists crop plants in managing stress and making agricultural systems more climate change resilient.

Different methods were used to elucidate the mode of action of thuricin S, a new class IId bacteriocin produced by Bacillus thuringiensis subsp. entomocidus HD198. According to cell viability tests, thuricin S was shown to exert a bactericidal effect on the sensitive cells of Bacillus thuringiensis subsp. darmastadiensis 10T. The use of the fluorescent probe 3,3'-dipropylthiadicarbocyanine iodide as an indicator proved that thuricin S interacts with the cytoplasmic membrane to dissipate the transmembrane potential. It was also demonstrated that thuricin S acts as a pore-forming bacteriocin, since it allows the nonpermeable stain propidium iodide to enter the cells. The loss of membrane integrity and the morphological changes in sensitive cells were visualized by scanning electron microscopy.