Respiration of 2,4,6-Trinitrotoluene by Pseudomonas sp. Strain JLR11

Abstract

Under anoxic conditions Pseudomonas sp. strain JLR11 can use 2,4,6-trinitrotoluene (TNT) as the sole N source, releasing nitrite from the aromatic ring and subsequently reducing it to ammonium and incorporating it into C skeletons. This study shows that TNT can also be used as a terminal electron acceptor in respiratory chains under anoxic conditions by Pseudomonas sp. strain JLR11. TNT-dependent proton translocation coupled to the reduction of TNT to aminonitrotoluenes has been observed in TNT-grown cells. This extrusion did not occur in nitrate-grown cells or in anaerobic TNT-grown cells treated with cyanide, a respiratory chain inhibitor. We have shown that in a membrane fraction prepared from Pseudomonas sp. strain JLR11 grown on TNT under anaerobic conditions, the synthesis of ATP was coupled to the oxidation of molecular hydrogen and to the reduction of TNT. This phosphorylation was uncoupled by gramicidin. Respiration by Pseudomonas sp. strain JLR11 is potentially useful for the biotreatment of TNT in polluted waters and soils, particularly in phytorhizoremediation, in which bacterial cells are transported to the deepest root zones, which are poor in oxygen.2,4,6-Trinitrotoluene (TNT) is a major contaminant in many military sites, where manufacturing and decommissioning operations generate large quantities of this explosive as a waste product. Much of this waste is deposited in the soil and in unlined lagoons, from which it often reaches groundwaters through leaching (16,21). TNT is toxic for many prokaryotes and eukaryotes, and it is mutagenic in Salmonella enterica serovar Typhimurium (23)(24)(25)27). This effect arises from the electrophilic nature of the substituent on the aromatic ring. In fact, TNT oxidizes biological reductants, causing toxicity both directly and through the formation of other reactive products, such as nitroarene radicals (14). Remediation is therefore urgently needed to clean up contaminated sites.A number of studies have found that mineralization of TNT under aerobic conditions is limited (2,5,7,8,10,20,26). In addition, many aerobic microbes reduce the nitro groups on the aromatic ring to nitroso and hydroxylamino groups, which have a high propensity to react with each other to produce azoxynitrotoluenes in the presence of oxygen (9). These azoxynitrotoluenes are recalcitrant to bioremediation. Degradation of TNT under anaerobic conditions has been explored as an alternative approach to remediation (3,4,6,11,12,13,18,22). This process has the potential advantages of rapid reduction at a low redox potential and of diminished polymerization reactions due to the absence of oxygen (9,12,18).Pseudomonas sp. strain JLR11, isolated from a wastewater treatment plant, is able to use nitrate, nitrite, and TNT as the N source under anoxic conditions (6). Mass balances with TNT have revealed that about 85% of the total N-TNT content was incorporated as cell biomass (6).Analyses of culture supernatants detected plausible pathway intermediates, such as 2,4,6-trinitrobenzaldehyde, 2-nitro-4-h...

Impact of Transgenic Tobacco on Trinitrotoluene (TNT) Contaminated Soil Community

“…Pseudomonads became prevalent in the highly contaminated soil. On multiple occasions pseudomonads have been isolated on the basis of their utilization of TNT as a nitrogen source, and their ability to transform TNT has been observed (30)(31)(32). It has been suggested that the prevalence of reports about pseudomonads transforming TNT in the literature was due to the ease with which this group of bacteria are cultured (33).…”

Biological Degradation of 2,4,6-Trinitrotoluene

“…More recently, Ramos and colleagues described a different mechanism for the anoxic degradation of TNT (68,69). They isolated a facultative Pseudomonas sp., designated strain JLR11, which was able to grow on TNT as the sole nitrogen source with glucose as a cosubstrate.…”

“…Another pathway has been described in Pseudomonas sp. strain JLR11 and involves nitrite release and further reduction to ammonium, with almost 85% of the nitrogen of TNT incorporated as organic nitrogen in the cells (68,69). In this review we intend to highlight the recent discovery of TNT as an alternative electron acceptor in respiratory chains of a facultative Pseudomonas strain (69).…”

Anaerobic Catabolism of Aromatic Compounds: a Genetic and Genomic View

“…Frequently, these compounds can be used as electron acceptors for respiration with the subsequent reduction and removal of the nitro substituents (108,109). However, some nitrogencontaining xenobiotics are finally channeled to single-aminoaromatic compounds such as anthranilate (2-aminobenzoate).…”

“…On the other hand, aromatic compounds can participate in anaerobic metabolism by serving as electron acceptors rather than electron donors, generally with accompanying modifications of ring substituents that do not perturb the benzene nucleus itself (e.g., chlorinated aromatics as electron acceptors in dehalorespiration, reduction of the acrylate side chain of aromatic compounds, and reduction of nitroaromatics, etc.) (45,88,105,108,109,128,160,169,338). As indicated above, different peripheral pathways involved in the anaerobic activation of a wide variety of (monocyclic) aromatic compounds lead to a few central aromatic intermediates, e.g., resorcinol (1,3-dihydroxybenzene), phloroglucinol (1,3,5-trihydroxybenzene), hydroxyhydroquinone (HHQ) (1,2, 4,-trihydroxybenzene), 6-hydroxynicotinate, hydroxybenzoylCoA, methylbenzoyl-CoA, aminobenzoyl-CoA, and benzoylCoA, with the latter being the most common and studied intermediate ( Fig.…”