| Nonionic detergents such as nonylphenol ethoxylate (NPE) are widely present in the environment due to their extensive use in industry. Moreover, NPE has recently been implicated in ecological toxicity, especially those involving the disruption of endocrine systems in aquatic animals. Although several studies have shown how NPE can be degraded by bacteria, however, studies on the possible conversion of NPEs to an environmentally compatible polymer do not exist. This study evaluated the ability of Ralstonia eutropha , to utilize NPE as a carbon source for the synthesis of poly[3-hydroxybutyrate] (PHB). Cells of Ralstonia eutropha were cultured in both batch and fed-batch fermentation for 96 hours in a phosphate-limited mineral salt medium containing 0.4mM of NPE as the sole source of carbon. The polymer was obtained using soxhlet extraction in hot chloroform and confirmed to be PHB by 13C-NMR. Optimization of PHB production was achieved by varying the experimental parameters. The addition of betaine enhanced PHB accumulation by 26%. The addition of yeast extract to the fermentation medium increased cell density while PHB accumulation was unaffected. Batch fermentation was more efficient than fed-batch. The average PHB content of batch fermentation was 21% while that of fed-batch was less than 5%. Increasing ammonium sulfate concentrations from 1 g/L to 5 g/L increased PHB yield from 26% to 42%. Similarly, dissolved oxygen concentration (DOC) of 113% oxygen saturation resulted in a PHB yield of 48 mg/L compared to 34 mg/L at 110% oxygen saturation. Based on the optimum fermentation conditions obtained from Ralstonia eutropha studies, comparative studies were conducted with Alcaligenes latus, Pseudomonas oleovorans, and recombinant Escherichia coli. In general, Alcaligenes latus accumulated the highest concentration (31%) of polymer. This was followed with 21% of polymer from Ralstonia eutropha, 19% polymer from Pseudomonas oleovorans, and 15% polymer from recombinant Escherichia coli. All organisms accumulated PHB within 72h. The results demonstrate that these bacteria are able to convert a toxic, hormonally active detergent into PHB—a nontoxic, completely biodegradable polymer. |
