Solubilization of tricalcium phosphate by P(3HB) accumulating Azotobacter chroococcum MAL-201

Abstract

Cells of Azotobacter chroococcum MAL-201 (MTCC 3853) are capable of accumulating the intracellular poly(3-hydroxybutyric acid) [P(3HB)], accounting for 65-71% of its cell dry weight and also capable of synthesizing the enzyme alkaline phosphatase (APase), when grown in glucose and tricalcium phosphate containing nitrogen-free modified Stockdale medium. The concentration of insoluble phosphate in broth medium was optimized as 0.25% (w/v) for growth and biosynthesis of APase. However, the suboptimal concentration of phosphate (0.1%, w/v) appeared as the best suited for accumulation of P(3HB) by the strain. The significant differences were observed in biosynthesis of polymer and APase enzyme under variable phosphate concentrations. Glucose, 3.0% (w/v) was recorded as the optimum concentration for all of the three parameters. The continuation of APase biosynthesis was observed during the period of significant decline in the cellular content of the polymer in the late phase of growth. In order to study the role of P(3HB), the rate of autodigestion of biopolymer and phosphate solubilization rate (k, mineralization constant) were determined in carbon-free medium under batch cultivation process and the parameters were found to be positively correlated. The maximum phosphate solubilization rate (k=0.0154) by the strain MAL-201 timed at the 10th hour of incubation when the rate of polymer degradation concomitantly attained its peak corresponding to 87mg/l/h and then declined gradually. Only a negligible amount of residual polymer remained undigested. These data strongly support the functional role of P(3HB) in response to multinutritional stress condition.