'Middle East Technical University, Faculty of Architecture'
Abstract
In this study, a new bacteriocin isolated from a Leuconostoc mesenteroides subsp. cremoris strain was purified to homogeneity by pH mediated cell adsorption-desorption, solid phase extraction with Amberlite XAD-16, cation-exchange chromatography and hydrophobic interaction chromatography. The purification resulted in an electrophoretically pure protein that was smaller than 6 kDa as judged by SDS-PAGE. The bacteriocin was found to be very hydrophobic and cationic and could be adsorbed by synthetic calcium silicate due to its cationic and especially hydrophobic nature. It was observed that this bacteriocin was sensitive to α-amylase in addition to proteinase K, trypsine, pepsine and chymotrypsine and had a bactericidal mode of action with a concomitant cell lysis. The results indicated that bacteriocin produced by Leuconostoc mesenteroides subsp. cremoris was more stable to combined effect of pH and heat than nisin, lacticin 481, lacticin 3147 and lactococcin G and was bactericidal between pH 2.0-12. It was found that the bacteriocin produced by Leuconostoc mesenteroides subsp. cremoris was stable to organic solvents and could be extracted with chloroform containing solvents efficiently for purification. The bacteriocin produced by Leuconostoc mesenteroides subsp. cremoris was found to have a strong inhibitory activity against Listeria innoqua, Listeria monocytogenes, Bacillus cereus, Enterococcus faecalis, Lactobacillus delbrueckii, Lactobacillus cremoris, other Leuconostoc meenteroides strains and gram-negative bacterium Pseudomonas fluorescens. Some of the insensitive bacteria were observed to be sensitive when high concentration of the bacteriocin was used.Ph.D. - Doctoral Progra
