Biodegradation of octyltin compounds by Cochliobolus lunatus and influence of xenobiotics on fungal fatty acid composition

• The fungus Cochliobolus lunatus was able to metabolize octyltin compounds.
• Fungal resistance to octyltins decreased with a reduction in the number of octyl groups bonded with a tin.
• Elimination of octyltins depended on the metabolic activity of the fungus.
• It is postulated that the process of degradation of octyltin compounds is mediated by cytochrome P-450.

The perturbation in the growth and fatty acid profile of the microscopic fungus Cochliobolus lunatus IM 4417 in the presence of octyltin compounds (trioctyltin – TOT, dioctyltin – DOT and monooctyltin – MOT) was studied. Fungal resistance to the tested organotins decreased with a reduction in the number of octyl groups bonded with a tin atom. Also, the fatty acid unsaturation index decreased according to the mentioned scheme. Among all tested octyltin compounds, TOT was removed with the highest efficiency. The efficiency of MOT removal was correlated with the initial concentration of the compounds and for concentrations 20 and 100 mg l−1 reached the value of 75% and 40%, respectively. Elimination of octyltins depended on the metabolic activity of the fungus and was not the result of passive sorption. During bioconversion of TOT the hydroxylated derivative of substrate was detected. Moreover, the addition of cytochrome P-450 inhibitors significantly reduced the metabolism of octyltin compounds. Thus, it is postulated that the process of degradation of octyltin compounds is similar to that described for tributyltin (TBT) and it is mediated by cytochrome P-450.