The Effect of Starvation and Polyphosphate Accumulation on Uranium Bioprecipitation in Bacillus cereus A 66

Starvation and accumulation of polyphosphates in bacteria is thought to result in the improvement of uranium bioprecipitation. The purpose of this study was to prove the effect of starvation and polyphosphate accumulation in the improvement of uranium bioprecipitation in Bacillus cereus A66. B. cereus A66 was precultured in Tryptone Glucose Yeast Extract (TGY), at room temperature (± 28oC) to logarithmic phase (± 16 hours). In the first treatment, preculture of B. cereus A66 was subjected to phosphate starvation in P-free medium, followed by transferring to the P-uptake medium for phosphate accumulation. To observe the uranium bioprecipitation response, the bacterial cell was transferred to 1 mM uranium solution. In the second treatment, B. cereus A66 preculture was immediately transferred to the uranium solution with no starvation phase and accumulation of polyphosphate. Whereas in the third treatment, B. cereus A66 preculture without the starvation phase was cultured in the P-uptake medium and then transferred to uranium solution. In the fourth treatment, B. cereus A66 was conditioned with phosphate starvation in P-free medium, followed by transferring to uranium solution. The second, third and fourth treatments were designed to confirm the effect of the first treatment in this study. The results showed that B. cereus A66 subjected to phosphate starvation was able to accumulate phosphate eight times more when it was transferred to P-uptake medium, compared to B. cereus A66 which did not experience phosphate starvation. In addition, B. cereus A66 which accumulated more phosphate also demonstrated an increase in uranium bioprecipitation as evidenced by 1.5 more uranium precipitated from the solution, compared to B. cereus A66 which was not subjected to phosphate starvation. This phenomenon was believed driven by polyphosphate metabolism controlled by the activity of the PPK and PPX genes. Overall, it was also shown that the more polyphosphate accumulated in cells, the more responsive uranium bioprecipitation in terms of uranium quantity being extracted from the solution and the efficiency of its uptake time. It is proposed that this strategy may be developed further for bioremediation of uranium-contaminated water and soil.