Isolation, characterization and mutagenesis of exopolysaccharide synthesizing new strains of lactic acid bacteria

Abstract

Bacterial exopolysaccharides have wide applications in various industries. In this perspective, it is essential to explore the natural biodiversity for novel strains of exopolysaccharide synthesizing lactic acid bacteria (LAB). Two novel isolates of lactic acid bacteria with higher enzyme activity were screened and characterized based on a battery of microscopic, staining, metabolic, physiological and antibiotic sensitivity tests. The two isolates of LAB named SPO and SPA were cocci shaped, Gram Positive, catalase negative, heterofermentative, vancomycin resistant, broad spectrum carbohydrate fermentating with exopolysaccharide synthesizing activity. EPS synthesizing activity was confirmed by activity staining of EPS using sucrose as substrate. This confirmed that the EPS produced was dextran and the enzyme responsible for its synthesis is dextransucrase. The enzyme activity of SPO was 3.8 U/ml and that of SPA was 3.4 U/ml. For strain improvement, the isolates were subjected to UV radiation. The isolate SPO did not give promising results. However, SPA after UV-mutagenesis, generated two novel mutants, SPAm1 and SPAm2. The enzyme activity of SPAm1 was 4.9 U/ml and that of SPAm2 was 4.7 U/ml. The mutants possessed about 40% enhanced enzyme activity over the wild type strain.