Biosynthesis of multiple biopolymers by Sinorhizobium meliloti CFR 14 in high cell density cultures through fed batch fermentation
2014
Shamala, T.R. | Rohinishree, Y.S. | Vijayendra, S.V.N.
Rhizobium spp. produce a variety of commercially important polymers during free living growth, which includes polyhydroxyalkanoate (PHA), exopolysaccharides (EPS), β-(1,2)-glucan, etc. Shake flask cultivation of Sinorhizobium meliloti CFR 14 for 72h with ammonium sulfate (0.318g/L of N) and sucrose (12.64g/L of C) resulted in 3.5g/L of biomass with 1.7g/L of PHA and 1.5g/L of EPS. Corresponding yields enhanced to 5.0, 2.5 and 2g/L, in a 48h batch fermentation process at 30°C, pH 7.0 and 40% air saturation level. Fed batch fermentation process with ammonium sulfate and sucrose as feed nutrients supported the production of 34.5g/L of biomass with 17.2g/L of PHA and 3.5g/L of EPS. Concentration of glycogen, cellular and excreted β-(1,2)-glucan were about 0.3g/L each under this condition. Fed batch process operated using ammonium hydroxide for dual purpose as a nitrogen source and for pH adjustment, lead to decreased biomass (29.6g/L) and PHA yields (9.4g/L). However, higher synthesis of EPS, glycogen, cellular and excreted β-(1,2)-glucan amounting to 9.0, 1.1, 1.3 and 2.0g/L, respectively, were obtained indicating that the fermentation conditions like pH, dissolved oxygen level, amount of carbon and nitrogen play a significant role in the synthesis of intra- and extra-cellular polymers by the free living cells of S. meliloti.
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