STUDIES ON BACTERIOCINS FROM ENVIRONMENTAL BACTERIA

Abstract

The present study is primarily concerned with bacteriocins from environmental bacteria. Different bacterial strains were isolated from various environments including hospital air, soil and sewage etc. A total of 51 isolates were screened for bacteriocinogeny, of which 41% (21 isolates) were exhibiting bacteriocinogeny. Two isolates, one of Pseudomonas sp. 40 and Bacillus subtilis strain15 were selected for further studies. Antimicrobial substance from Pseudomonas sp. 40 was neither sensitive to proteolytic enzymes nor showed any antibacterial activity on SDS-PAGE indicating its possible non-proteinaceous nature and hence further studies were not carried out on this strain. Only Bacillus subtilis stain 15 was further studied as it was producing some antimicrobial substance of protein in nature. BLIS of Bacillus subtilis strain 15 was produced during the late exponential-phase or at the beginning of stationary-phase. The inhibitory substance/BLIS was partially purified by ammonium sulphate precipitation. The antimicrobial substance was characterized as a bacteriocins-like inhibitory substance with a molecular weight ranged between 3-5 kDa as determined by SDS-PAGE. BLIS showed the inhibitory activity against locally isolated Bacillus species as well as Bacillus subtilis ATCC 6633 and Bacillus cereus ATCC 11778, Listeria monocytogenes, Staphylococcus aureus, Staphylococcus epidermidis and also showed slight activity against Salmonella typhi and Shigella dysenteriae and those involved in the food-poisoning and spoilage such as Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes, Micrococcus luteus were inhibited that indicates its possible application in food preservation. BLIS acted bacteriostatically rather than bacteriocidally, on the sensitive cells. It may exhert bactericidal action at higher concentrations. BLIS under study was heat stable up to 80°C as its activity was not affected at this temperature. The BLIS retained its activity over a wide range of pH i.e., from 3-9. It was sensitive to proteinase-K, and α-chymotrypsin indicating about its nature as protein. Its activity remained unaffected in presence of organic solvents like acetone, chloroform, methanol and EDTA except ethyl-alcohol. BLIS from Bacillus subtilis strain 15 showed the effective inhibition of superoxide production in both neutrophils and macrophages. It also had inhibitory effect on whole-blood. The inhibition of superoxide production shows that BLIS may have anti- inflammatory or immuno-suppressive effect. In addition to immunomodulatory activity, BLIS from Bacillus subtilis strain 15 had moderate anti-oxidant activity indicating its probable role in anti-tumorogenic activity.