Aerobic TNT reduction via 2-hydroxylamino-4,6-dinitrotoluene by Pseudomonas aeruginosa strain MX isolated from munitions-contaminated soil

Bioremediation of munitions-contaminated soil requires effective transformation and detoxification of high concentrations of 2,4,6-trinitrotoluene (TNT). Pseudomonas aeruginosa strain MX, isolated from munitions-contaminated soil, aerobically transformed TNT (100 mg/L) in culture medium within 15 h, causing transient accumulation of hydroxylaminodinitrotoluenes (HADNTs). The predominance of 2-hydroxylamino-4,6-dinitrotoluene (2HADNT), as well as 2-amino-4,6-dinitrotoluene (2ADNT) and 4,4′,6,6′-tetranitro-2,2′-azoxytoluene (2,2′AZT), indicated preferential reduction of the TNT ortho nitro group. While only 12% of the TNT was transformed to 2ADNT, up to 65% was transformed to tetranitroazoxytoluenes (AZTs), which accumulated as a precipitate. The precipitate was formed by microscopic particles adhering to bacterial cells, which subsequently formed clusters containing lysed cells. Toxicity toward bacteria was primarily attributed to 2ADNT, because pure AZTs preincubated with sterile medium had little effect on the strain. While the culture medium containing TNT exhibited toxicity toward corn (Zea mays L.) and witchgrass (Panicum capillare L.), little phytotoxicity was observed after incubating with P. aeruginosa strain MX for 4 d. Strong binding of HADNTs to soil and low AZT bioavailability may further promote the detoxification of TNT in soil.