A two-component monooxygenase initiates a novel 2-bromo-4-nitrophenol catabolic pathway in newly isolated Cupriavidus sp. strain NyZ375

摘要

As a vital byproduct of chemical intermediates for pesticides and cytotoxin inhibitors, 2-bromo-4-nitrophenol (2B4NP) is toxic to aquatic life. However, bacterial cultures mineralizing 2B4NP have not been reported. In this study, Cupriavidus sp. strain NyZ375 was isolated from aromatics-polluted soil and identified by 16S rRNA gene sequencing. Via an oxidative pathway, it grows on 120 mu M 2B4NP as the only carbon source, releasing approximately equivalent amount of nitrite. Three genes (bnpABC) in a 4.8-kb DNA fragment from a draft genome was found to be responsible for the initial reactions in 2B4NP degradation. BnpAB are the monooxygenase and flavin reductase components, respectively, catalyzing the monooxygenation of 2B4NP to bromohydroquinone (BHQ, 63%) and 1,2,4-benzenetriol (BT, 37%) with concomitant nitrite release, in the presence of NADH and FAD. BnpC is a hydroxyquinol 1,2-dioxygenase catalyzing the ring-cleavage oxidation of BT to maleylacetate. The by-product BHQ was not further degraded by strain NyZ375 but was not toxic to its growth at a concentration of 100 mu M. It can be tentatively concluded that BnpAB is evolutionary close to the 2,4,6-trichlorophenol monooxygenase TcpAX from Cupriavidus necator JMP134. The 2B4NP catabolism by this new isolate illustrates a pathway distinct from those of all identified 2-chloro-4-nitrophenol utilizers.