Degradation of nitrophenols by nocardioides sp. NSP41 and rhodococcus sp. DNP505

Abstract

Nitrophenol-degrading bacteria were isolated from industrial wastewater by selective enrichment cultures. On the basis of their chemotaxonomic and phylogenetic characteristics, p-nitrophenol-degrading strain NSP41 was identified as a new species of the genus Nocardioides (Nocardioides nitrophenolicus $NSP41^T)$ and 2,4-dinitrophenol-degrading strain DNP505 was identified as a new species of the genus Rhodococcus (Rhodococcus koreensis $DNP505^T)$. The effect of phenol supplementation on the degradation of p-nitrophenol by Nocardioides sp. NSP41 was investigated. Strain NSP41 was able to degrade p-nitrophenol and phenol simultaneously. In the same concentration (molar base) of p-nitrophenol and phenol, both compounds were degraded simultaneously at the same rate without accumulation of any other intermediates. In low phenol concentration, phenol was completely mineralized before p-nitrophenol degradation. After exhaustion of phenol, p-nitrophenol was partially transformed to 4-nitrocatechol. Concerning high phenol concentration, p-nitrophenol was degraded faster and completely exhausted before phenol degradation. Kinetically, the addition of phenol enhanced the apparent p-nitrophenol degradation rate, which may be due to the increased cell mass by the assimilation of phenol. The pathway for simultaneous degradation of p-nitrophenol and phenol was investigated in Nocardioides sp. NSP41. Strain NSP41 degraded p-nitrophenol via a hydroquinone pathway, while degraded phenol through a catechol pathway. Resting cells and enzyme extracts from cells grown on p-nitrophenol, phenol, and the mixture of p-nitrophenol and phenol indicated that there are two alternative pathways for the metabolism of p-nitrophenol and phenol in strain NSP41 and two pathways were expressed depending on the substrate used. During the simultaneous degradation of p-nitrophenol and phenol, both hydroquinone pathway and catechol pathway were induced and expressed simultaneously. In order to eluc...