Rock phosphate solubilization by immobilized cells of Enterobacter sp. in fermentation and soil conditions

An Enterobacter sp., a phosphate-solubilizing bacterium, was immobilized in agar. Various amounts of the immobilized bioparticles were applied in a repeated-batch fermentation process in order to solubilize Venezuelan rock phosphate. A total production of 388 mg and 403 mg soluble P/l was obtained for 2.0 g rock phosphate/l in flasks containing 10 ml and 20 ml agar beads, respectively, that was significantly higher compared to a free-cell single-batch control. Whole and destroyed immobilized bioparticles were introduced into a soil enriched with rock phosphate to improve the growth of onion plants. Compared to the control supplemented with a free-cell bacterial suspension, the results showed at least equal plant growth of 80 mg/pot and shoot P concentration of 82 μg/plant when 10 destroyed beads were applied per pot.