Isolation and characterization of salinity tolerant nitrogen fixing bacteria from Sesbania sesban (L) root nodules

Abstract

Abstract This work was aimed to isolate and characterize Rhizobia from Sesbania Sesban root nodules growing in different parts of Mumbai metropolitan area. Root nodules from these plant samples were harvested and 120 test isolates were obtained. A total of 75 obtained isolates were found to show poor absorption of Congo red when grown on yeast extract mannitol agar with 2% NaCl. These isolates were further studied for their morphological and biochemical characteristics along with Rhizobium leguminosarum as a reference culture. The isolates were found to be gram negative rods and exhibited a rapid growth as evident from bromothymol blue test. Biochemical and phenotypic characterization of all 75 isolates revealed them to be Rhizobium species. Furthermore, 8 representative isolates from 8 different Mumbai Metropolitan locations were used for genotypic analysis by 16S rRNA sequencing. All 8 isolates were shown to have inhibitory effect on growth when tested on different salt concentration. As the NaCl concentration was increased from 0.1 to 20%, the growth started declining. Further, at 30% concentration, an absolute growth inhibition was observed. The isolates exhibited noteworthy growth at pH 6.0 to 11.0. The pH of 7.0–8.0 and a temperature of 28 °C was found to be optimum for growth. A high salinity (up to 20%) and pH tolerance of these species make them suitable to be used as biofertilizers in unfavorable environmental conditions for legumes cropping and could also help to reduce the use of chemical fertilizers.