Implications of cysteine metabolism in the heavy metal response in Trichoderma harzianum and in three Fusarium species

We studied the ability of four different fungal species, Trichoderma harzianum, Fusarium antophyllum, Fusarium compactum and Fusarium phyllophilum, to grow in the presence of heavy metals, and monitored their cysteine and glutathione content and the activity of O-acetylserine(thiol)lyase (OASTL), which is involved in cysteine biosynthesis. Zn and Pb did not affect fungal growth or sporulation at the concentrations used, whereas Cd and Hg did. In most cases, cysteine and glutathione content was higher when fungi were grown in the presence of toxic metals. As T. harzianum and F. phyllophilum presented the best growth rate on Cd and Hg, they were selected to further analyse the accumulation of toxic metals. Both species accumulated the four metals in large amounts. Using degenerate oligonucleotides based on fungal OASTL genes present in databases, partial OASTL DNA sequences were cloned by PCR from T. harzianum and F. phyllophilum, and the regulation of the OASTL genes under metal stress was analyzed. Cd produced the strongest increase in OASTL activity and mRNA levels in both fungi. The results suggest a possible correlation between cysteine metabolism and the heavy metal response in fungi.