Homologous npdGI genes in 2,4-dinitrophenol- and 4-nitrophenol-degrading Rhodococcus spp.

Rhodococcus (opacus) erythropolis HL PM-1 grows on 2,4,6-trinitrophenol or 2,4-dinitrophenol (2,4-DNP) as a sole nitrogen source. The NADPH-dependent F-420 reductase (NDFR; encoded by npdG) and the hydride transferase II (HTII; encoded by npdI) of the strain were previously shown to convert both nitrophenols to their respective hydride Meisenheimer complexes. In the present study, npdG and npdI were amplified from six 2,4-DNP degrading Rhodococcus spp. The genes showed sequence similarities of 86 to 99% to the respective npd genes of strain HL PM-I. Heterologous expression of the npdG and npdI genes showed that they were involved in 2,4-DNP degradation. Sequence analyses of both the NDFRs and the HTIIs revealed conserved domains which may be involved in binding of NADPH or F-420. Phylogenetic analyses of the NDFRs showed that they represent a new group in the family of F-420-dependent NADPH reductases. Phylogenetic analyses of the HTIIs revealed that they form an additional group in the family of F-420-dependent glucose-6-phosphate dehydrogenases and F-420-dependent N-5,N-10-methylenetetrahydromethanopterin reductases. Thus, the NDFRs and the HTIIs may each represent a novel group of F-420-dependent enzymes involved in catabolism.