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. Introduction Since time immemorial, lactic acid bacteria are regarded as food grade micro-organisms. LAB have found wide applications as food preservatives, flavouring and texturizing agents for centuries [1] and are now used as starter culture in dairy industry, meat and vegetable fermentation. LAB have received great attention as the major group of probiotic bacteria promoting the growth of gut micro flora [2]. LAB are also reported to cure diarrhoea, irritable bowel disorder, allergies, lactose intolerance, urinary tract infections and to stimulate immunity (3,4,5). LAB capable of secreting antimicrobial peptides are used as food preservatives as well as health-promoting agents for humans [6]. Lactic acid bacteria have attracted immense commercial interests, for their capacity to secrete a host of exopolysaccharides having industrially useful physico-chemical properties [7,8]. Dextrans are a class of exopolysaccharides synthesised by Lactobacillus, Leuconostoc and Streptococcus belonging to LAB family. Sucrose is hydrolysed by the enzyme dextransucrase and the resultant D-glucosyl moieties are polymerised to produce dextran. Dextrans are employed as blood plasma substitutes, plasminogen activators, antithrombogenic agents and in treatment of iron deficiency anaemia [9,10]. Dextrans have also tremendous usage in matrix preparation of chromatography columns [10]. Dextrans have major use in food formulations as stabilizing, emulsifying, texturizing and gelling agent. Dextran is reported to enhance biocompatibility of biomaterials [11]. Considering the grand commercial usage of the dextrans, it is essential to discover novel isolates of LAB synthesizing bioactive exopolysaccharides. It is important to garner sufficient information about the characteristics of the EPS producing strains, as the optimal growth conditions, carbohydrate fermentation ability, antibiotic sensitivity studies have practical implications in maximizing the dextran production on large scale. The development of novel approaches in food and in pharmaceutoclinical therapies is broadening the potential for using lactic acid bacteria. [12]. Apart from screening the biodiversity for selection of new isolates, UV induced mutagenesis of the existing strains for improvement is a promising strategy. UV mutagenesis was carried out on the strains of L. delbrueckii (NCIM 2365) and screened four novel mutants exhibiting higher lactic acid productivity and yield with faster growth rates and shorter lag phases were reported [13]. The present study reports the isolation of two new strains of lactic acid bacteria from the soil samples, their characterization. UV mutagenesis as a tool for strain improvemen
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