Degradation of 4-Nitrophenol, 2-Chloro-4-nitrophenol, and 2,4-Dinitrophenol by Rhodococcus imtechensis Strain RKJ300

Abstract

A bacterial strain Rhodococcus imtechensis RKJ300 (= MTCC 7085(T) = JCM 13270(T)) was isolated from pesticide-contaminated soil of Punjab by the enrichment technique on minimal medium containing 4-nitrophenol. Strain RKJ300 is capable of utilizing 4-nitrophenol, 2-chloro-4-nitrophenol, and 2,4-dinitrophenol as sole sources of carbon and energy. The strain involved both oxidative and reductive catabolic mechanisms for initial transformation of these compounds. In the case of 2-chloro-4-nitrophenol, colorimetric analysis indicated that nitrite release was followed by stoichiometric elimination of chloride ions. Experiments using whole cells and cell-free extracts showed chlorohydroquinone and hydroquinone as the intermediates of 2-chloro-4-nitrophenol degradation. This is the first report of degradation on 2-chloro-4-nitrophenol by a bacterium under aerobic condition to the best of our knowledge. However, pathways for degradation of 4-nitrophenol and 2,4-dinitrophenol were similar to those reported in other strains of Rhodococcus. Laboratory-scale soil microcosm studies demonstrated that the organism was capable of degrading a mixture of nitrophenols simultaneously, indicating its applicability toward in situ bioremediation of contaminated sites. The fate of the augmented strain as monitored by the plate-counting method and hybridization technique was found to be fairly stable throughout the period of microcosm experiments.

A Two-Component para -Nitrophenol Monooxygenase Initiates a Novel 2-Chloro-4-Nitrophenol Catabolism Pathway in Rhodococcus imtechensis RKJ300

“…To our surprise, BT was identified as the ring cleavage substrate during 2C4NP degradation in this strain, rather than HQ as previously proposed (4). On the other hand, the two-component (TC) para-nitrophenol (PNP) monooxygenase PnpA1A2 in this strain was found to be able to catalyze the sequential denitration and dechlorination of 2C4NP to BT, and pnpA1 is essential for strain RKJ300 to utilize 2C4NP and PNP.…”

“…strain SJ98 (14). However, no such information has been reported in Gram-positive bacteria, although two Gram-positive 2C4NP utilizers (4,5) were isolated. In this study, the high transcription of the pnp cluster in 2C4NP-and PNP-induced cells indicated that the enzymes encoded by the pnp genes were likely involved in both 2C4NP catabolism and PNP catabolism in strain RKJ300.…”

“…However, no investigation has been reported at the genetic and enzymatic levels for the 2C4NP catabolism in Gram-positive utilizers Arthrobacter sp. strain SJCon (5) and Rhodococcus imtechensis RKJ300 (4).…”

Physiology, Biochemistry, and Applications of F420- and Fo-Dependent Redox Reactions

“…The results of comparative genomics suggest that homologs of these proteins are exclusively encoded by the genera Nocardioides, Rhodococcus, and Nocardia among presently sequenced organisms. Empirical studies consistently indicate that equivalent enzymatic pathways can degrade nitroaromatic compounds in five additional Rhodococcus species (398,(436)(437)(438) and three Nocardioides species (54,396,397,432,439). Beyond picrate and 2,4-dinitrophenol, LLHTs are involved in the biodegradation of other nitroaromatic compounds.…”

Novel Pathway for the Degradation of 2-Chloro-4-Nitrobenzoic Acid by Acinetobacter sp. Strain RKJ12

“…The microbial degradation of NACs has been extensively investigated (15,32,40,41). Although structurally related to the NACs, the CNACs are extremely resistant (12,31,49,50,51) to microbial degradation due to the simultaneous existence of two strong electron-withdrawing chlorine and nitro groups; thus, the knowledge of its microbial degradation is very limited. Most investigations of the degradation of CNACs have revealed cometabolic transformations.…”