3-nitroadipate, a metabolic intermediate for mineralization of 2, 4-dinitrophenol by a new strain of a Rhodococcus species

Abstract

The bacterial strain RB1 has been isolated by enrichment cultivation with 2,4-dinitrophenol as the sole nitrogen, carbon, and energy source and characterized, on the basis of 16S rRNA gene sequence comparison, as a Rhodococcus species closely related to Rhodococcus opacus. Rhodococcus sp. strain RB1 degrades 2,4-dinitrophenol, releasing the two nitro groups from the compound as nitrite. The release of nitro groups from 2,4-dinitrophenol occurs in two steps. First, the 2-nitro group is removed as nitrite, with the production of an aliphatic nitro compound identified by 1H nuclear magnetic resonance and mass spectrometry as 3-nitroadipate. Then, this metabolic derivative is further metabolized, releasing its nitro group as nitrite. Full nitrite assimilation upon reduction to ammonia requires that an additional carbon source be supplied to the medium.

FIG. 1

Time course of cell growth, 2,4-DNP uptake, and nitrite release by Rhodococcus strain RB1 cultured with 2,4-DNP as the sole nitrogen source. Cells were grown under aerobic conditions with 50 mM sodium acetate and 0.5 mM 2,4-DNP. A₆₀₀ (•), 2,4-DNP concentration (○), and nitrite concentration (▴) were measured at the indicated times.

FIG. 2

Time course of cell growth, 2,4-DNP uptake, and nitrite release by Rhodococcus strain RB1 cultured with 2,4-DNP and ammonium as nitrogen sources. Cells were grown under aerobic conditions with 50 mM sodium acetate, 0.5 mM 2,4-DNP, and 2 mM ammonium chloride. At the times indicated, A₆₀₀ (•), 2,4-DNP concentration (○), and nitrite concentration (▴) were measured. The arrow indicates the time at which the concentration of ammonium in the medium was undetectable.

FIG. 3

Proposed pathway for the degradation of 2,4-DNP by Rhodococcus. Compounds in brackets are hypothetical intermediates. The formation of 4,6-dinitrohexanoate has been described previously (12). TAC, tricarboxylic acid cycle.