Effect of nickel, copper, and zinc on emulsifier production and saturation of cellular fatty acids in the filamentous fungus Curvularia lunata

In the first step of this investigation the toxicity of Ni2+, Cu2+, and Zn2+ ions to the emulsifier producing strain of Curvularia lunata was assessed. Among all the heavy metals studied, Ni2+ ions were found to be the most toxic to C. lunata, whereas Zn2+ ions exhibited the lowest toxicity. Moreover, only Ni2+, when used at sublethal concentration (5 mM) caused lysis of some hyphal tip cells after a short-term exposure (5 h). In the next step, emulsifier production, accumulation of heavy metals by mycelia and emulsifier as well as saturation of cellular fatty acids were examined in 48-h-old cultures where fungal growth intensity was not inhibited by heavy metals (in the presence of Ni2+, Cu2+, and Zn2+ ions at the initial concentration of 1, 5, and 15 mM, respectively) and in cultures where approximately 50% biomass inhibition occurred (in the presence of Ni2+, Cu2+, and Zn2+ ions at the initial concentrations of 3, 10, and 17.5 mM, respectively). Among all the heavy metals studied only Ni2+ ions did not induce emulsifier production. As compared with the control, only biomass treated with Ni2+ ions displayed an increase in total lipid saturation. This effect resulted mainly from the decrease in linoleic acid (18:2) content correlated with the increase in the amount of stearic acid (18:0). The possible mechanisms by which Ni2+ ions could alter the fatty acid profile of C. lunata and the protective role of the emulsifier were also discussed.