Effect of carbon and nitrogen sources on exopolysacharide production by rhizobial isolates from root nodules of Vigna trilobata

Abstract

Twenty five (25) rhizobial strains were isolated from root nodules of Vigna trilobata cultivars grew in soils collected from all districts of Andhra Pradesh, India. Five out of 25 rhizobial strains which produced copious amount of Exopolysaccharides (EPS) on Yeast Extract Mannitol Agar (YMA) medium with congo red were identified by sequencing of their 16S rDNAs. The amount of EPS produced by these five strains increased during the first 72 h of incubation but it declined afterwards. The amount of EPS produced correlated positively with increase in mannitol concentration from 1 to 3% (m/v). However, there was a decrease in EPS production when mannitol concentration was equal or higher than 4%. All the five strains studied preferred mannitol and sodium nitrate as the best carbon and nitrogen sources for EPS production. Sinorhizobium kostiense MRR104 produced maximum levels of EPS 892 mg/100 ml when mannitol was used as carbon source, while S. xinjiangense MRR110 produced maximum levels of EPS 377 mg/100 ml when sodium nitrate was used as nitrogen source. Variation among the rhizobial strains in utilization of carbon and nitrogen sources for EPS production was clearly evident from this study. All the strains analysed in the present study can be exploited for production of commercial biopolymer (gum), due to their non pathogenic nature and their ability to produce copious amounts of EPS when compared to strains studied in earlier reports.

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“…The amylase activity by the isolated Bacillus pumilus DS5 strain was observed at 48 h, and the maximum amylase activity obtained was 102.4 U/ml. Synorhizobium kostiense MRR 104 produced the maximum amount of EPS and growth after 48 hours of incubation 10 .…”

“…To determine the effect of carbon sources on amylase production of the strain, different carbon sources like maltose, lactose, fructose, sucrose, dextrose, starch, mannitol, arabinose, xylose, glycerol and inositol 1% were added separately to the optimized medium 10 . Furthermore, the effect of varying concentrations of the best carbon source (0.5 -5%) on amylase production was also determined.…”