Continuous degradation of mixtures of 4-nitrobenzoate and 4-aminobenzoate by immobilized cells of Burkholderia cepacia strain PB4

Although isolated on 4-aminobenzoate, Burk-holderia cepacia strain PB4 is a lso able to grow on 4-nitrobenzoate. Degradation of an equimolar mixture of the nitroaromatic compound 4-nitrobenzoate and its corresponding aminoarom atic derivative 4-aminobenzoate by this strain was investigated. Batch expe riments showed that, irrespective of preculturing conditions, both compound s were degraded simultaneously. The mixture-degrading ability of B. cepacia strain PB4 was subsequently tested in continuous packed bed reactors (PBR) with the strain immobilized on Celite grade R-633 or R-635. Higher degrada tion rates were achieved with the larger particles of Celite R-635. Maximum simultaneous degradation rates per liter of packed bed of 0.925 mmol l(-1) h(-1) 4-nitrobenzoate and 4-aminobenzoate were obtained for an applied loa ding rate of the same value (0.925 mmol l(-1) h(-1) of each compound). Even when the applied load was not removed in its entirety, neither of the two compounds was degraded preferentially but a percentage of both of them was mineralized. The present study shows the possibility for a pure strain to b iodegrade not only a nitroaromatic compound (4-nitrobenzoate) but also its corresponding amino derivative (4-aminobenzoate) continuously and simultane ously.