Induction of metallothioneins in the heavy metal resistant fungus Beauveria bassiana exposed to copper or cadmium

In our previous studies, we have isolated a copper-resistant (10 mM-Cu) fun gus deuteromycotina Beauveria bassiana and examined that the fungus B. bass iana had additional resistances towards zinc, cadmium and lead. When B. bas siana was exposed to copper, copper was accumulated in the mycelia and a co pper-metallothionein (MT) was induced. In contrast, to vertebrate MTs, whic h bind different metal ions, fungal MTs were reported to contain exclusivel y copper ions, however, whether if other metal ions, such as cadmium, could induce a MT in fungal mycelia or not, still remain unknown. The purpose of this study are to investigate the inducibility of cadmium metallothionein in the fungus B. bassiana by cadmium exposure. This paper deals with the co mparison of the chromatographic behavior and spectroscopic properties of ca dmium-binding protein with copper-binding protein from this fungus, exposed to cadmium or copper. Upon exposure the fungus B. bassiana to cadmium (0.5 mM), cadmium was incorporated and accumulated in the mycelia. Incorporated cadmium was eluted in low molecular weight region by the gel filtration. T he elution profile showed very similar pattern to a copper-binding protein and revealed the existence of a low molecular weight, cadmium-binding prote in. The absorption spectra which was lack of 280 nm showed a properties of metallothioneins and shoulder around 250 nm was typical of Cd(II)-thiolate coordination. Upon removal of cadmium by acidification, the spectrum indica ted a clear loss of the absorption shoulder. This feature can be interprete d as a manifestation of the cadmium thiolate cluster structure in the molec ules. Exposure to cadmium may cause to induce a MT (class II type of MT) wh ich might be family 8 according to a new classification in the fungus B. ba ssiana. It was suggested that MT could be induced in the fungus by not only copper but also cadmium exposure.