Reductive transformation of 2,4,6-Trinitrotoluene by Yarrowia lipolytica AN-L15 under conditions of different initial pH of the culture medium or in the presence of ferrihydrite

Abstract

Batch and column studies were conducted to examine the difference in the transformation pathways of 2,4,6-trinitrotoluene (TNT) reduction by a hemiascomycetous yeast (Yarrowia lipolytica AN-L15) under conditions of different initial pH of the culture medium or in the presence or absence of ferrihydrite. Using high performance liquid chromatography (HPLC), it was observed that Y. lipolytica AN-L15 was able to transform TNT at three different initial proton concentrations of the culture medium: pH 7.0, pH 6.5, and pH 4.5. In the presence of TNT, Y. lipolytica AN-L15 showed preferential growth (OD₆₀₀) at the lower initial pH of 4.5. The increased growth (OD₆₀₀) resulted in increased reduction of TNT-metabolites in the culture medium with an initial pH of 4.5, as compared to, the culture medium with an initial pH of 6.5 or the culture medium with an initial pH of 7.0. TNT transformation via aromatic ring reduction was the major transformation pathway observed, with the major metabolite being 3-H -̄TNT. 4-hydroxylaminodinitrotoluene (4-HADNT) was the major metabolite of the nitro-group reduction pathway. In the presence of ferrihydrite at a pH of 7.0, the transformation of TNT by Y. lipolytica AN-L15 showed a change in the transformation pathway. Nitro-group reduction was the major pathway of TNT transformation in the presence of ferrihydrite with 4-HADNT and 2-aminodinitrotoluene (4-ADNT) being the major metabolites formed. The time it took to reduce TNT was longer and the concentrations of TNT-metabolites were lower in the presence of ferrihydrite than in its absence. This may have been due to competition for available electrons between TNT and TNT-metabolites and Fe(III). It is also possible that some of the intermediate products of TNT transformation were oxidized back to TNT-metabolites by Fe(III) resulting in lower concentrations of TNT-metabolites and increased concentrations of Fe(II). This study demonstrates the complexity of the interactions of various environmental parameters, under controlled laboratory conditions, in the transformation of TNT by Y. lipolytica AN-L15.