Screening and characterization of exopolysaccharide producing Lactobacillus spp.

Abstract

The present study was undertaken with the objective to screen promising L. gasseri, L. reuteri and L. helveticus isolates for the Exopolysaccharide (EPS) production and their characterization through biochemical and molecular tests. A total of 7 isolates of L. gasseri and 37 isolates of L. reuteri and one isolate of L. helveticus were screened for the EPS production through various tests and finally L. gasseri Lg62 and L. helveticus V3 were selected for the further study. The most promising EPSs producing isolates i.e. V3 and Lg62 gave a prominent growth on RR-MRS agar plate whereas Lg63 and Lg50A were not so prominent on RR-MRS agar plate. V3 and Lg62 showed better viscosity than Lg63 and Lg50A. V3 showed viscosity and corresponding O.D. in the range of 1.100 -1.677 cp and 0.753-1.207 (at 525nm) respectively at 42⁰C and 1.050-1.242 cp and 0.673-0.952 (at 525nm) at 37⁰C respectively. The isolates were found to be purple coloured Gram-positive rods of varying size under microscope. Lactobacillus cultures were catalase negative. V3 showed growth when incubated in MRS broth at 37⁰C as well as at 42⁰C for 24-48 hrs, in terms of turbidity whereas there was no turbidity at 15⁰C. In the arginine hydrolysis test neither LG62 nor V3 showed positive reaction. Both the EPS+ cultures produced acid from glucose, maltose, fructose and sucrose on incubation at 37⁰C for 24 hours. None of the culture produced gas in glucose. Both the cultures V3 and Lg62 showed growth at 4% NaCl concentration and changed the colour of the media from purple to yellow. Growth of V3 was not detected in 6.5% NaCl concentration whereas Lg62 showed growth in the same concentration. After identification of the selected cultures by biochemical techniques they were further confirmed by PCR using species specific primers.