335회 Transformations of 2,4,6-Trinitrotoluene (TNT) by Degrading Micro…

335회

연사 : 송 홍 규, 강원대학교 생명과학부

제목:  Transformations of 2,4,6-Trinitrotoluene (TNT) by Degrading Microorganisms

Abstract

The study on degradation of 2,4,6-trinitrotoluene (TNT) by several white rot fungi isolated in Korea was carried out to examine their capability to metabolize TNT. Some fungal strains completely removed TNT during several days of incubation and showed higher removal rates than that of Phanerochaete chrysosporium used as a comparative control. In the culture of Irpex lacteus, up to 200 mg/L of TNT was removed within 12 hours after adding it to a 5-day old culture. Interestingly I. lacteus can metabolize TNT with two different initial transformation pathways. In one metabolic pathway of TNT a nitro group was removed from the aromatic ring of TNT. Formation of hydride-Meisenheimer complex of TNT (H--TNT), which is an important intermediate, was confirmed with LC/MS and LC/photodiodearray detector. 2,4-Dintrotoluene and nitrite produced by the denitration of H--TNT supported this transformation pathway. In the other TNT pathway, nitro groups in TNT were successively reduced to amine groups via hydroxylamines. The initial formation of hydroxylamino-dinitrotoluenes (2- and 4- OHAmDNT) was observed, and followed by their successive transformation to aminodinitrotoluenes (2- and 4-AmDNT). Transformation of TNT to AmDNTs via OHAmDNTs was fast, but the next step was slow. Mineralization of [U-14C]TNT by I. lacteus was tested in static and shaken cultures. The mineralization rate of TNT in static culture was higher than that in shaken culture, and addition of Tween 80 enhanced the mineralization of TNT in static culture.

    Several TNT-degrading bacteria were isolated from activated sludge in two step continuous stirred tank reactors. A strain which showed the highest TNT-degrading activity was identified as Enterobacter cancerogenus. TNT was completely disappeared within 6 hours of further incubation when 100 mg/L of TNT was added into 1-day pregrown Enterobacter culture. OHAmDNTs, AmDNTs, and diaminonitrotoluenes (DAmNTs) were detected as main TNT metabolites. The aerobic and anaerobic TNT degradation by Enterobacter sp. were also compared. Finally, Enterobacter sp. was tested for its ability to mineralize TNT. The mineralization rate of Enterobacter sp. was much lower than those of white rot fungi reported, but was higher than those of other bacteria reported.