Bioproduction of Ascorbic Acid and Its Optimization by a Rhizobium sp. from Root Nodules of Sesbania cannabina

The microsymbiont was isolated from the root nodules of Sesbania cannabina (Wild.) Pers. Initially eleven strains were isolated and all were identified as Rhizobium sp. through different physiological and biochemical tests. Ascorbic acid (AsA) production by all the isolates was checked in glucose supplemented basal medium. All the strains had the capacity to produce AsA in the culture filtrate, however to different extent. The isolate S5 showed highest AsA production (160 μg mL−1) in the culture filtrate and hence subsequent experiments were carried out with S5 strain. Both the growth and AsA production phase were started simultaneously at the onset of inoculation, and reached maximum at 24 h. The optimum pH for the AsA production was 7.0. Production of AsA by the isolate was increased to a greater extent over control when the basal medium was supplemented individually with glucose (0.7 %), thiamine-hydrochloride (200 μg L−1), biotin (200 μg L−1), glycine (0.15 %) and sodium dodecyl sulfate (1.0 μg mL−1). AsA production was increased by 278.3 % at a time when all the individual best supplements were added to the basal medium. The results of the Basic Local Alignment Search Tool search of the 16S ribosomal ribonucleic acid gene sequences indicated that S5 isolate was closely related to Rhizobium sp. Moreover, it was found that root contained very negligible amount of AsA than the root nodule. The possible role of AsA production by the Rhizobium sp. in the legume-rhizobia symbiosis has been discussed. © 2016, The National Academy of Sciences, India.