Heavy metal resistance of the extreme acidotolerant filamentous fungus Bispora sp.

To obtain information on the importance of membrane and zeta potentials as repelling or facilitating forces during the uptake of cationic trace elemen ts, the heavy metal content and the growth resistance of the acidotolerant fungus Bispora. sp. to heavy metals were compared at pH 1.0 and pH 7.0. Cu, Co, Ni, Cd, Cr, and La contents of the fungus were significantly lower at pH 1.0 than at pH 7.0. A similar pH effect occurred with cationic macro ele ments such as Na, Mg, Ca, Fe, and Mn. Only K and Zn exhibited higher levels at pH 1.0 in the fungus than at pH 7.0. Macro and micro elements present i n the medium in anionic form (sulfate, chloride) showed the opposite patter n to cations: Contents were higher at pH 1.0 than at pH 7.0. Minerals prese nt at pH 1.0 predominantly in the electrical neutral, protonated form (phos phate, borate) exhibited a similar cell content at both acid and neutral pH (P) or a higher content at neutral pH than at acid pH (B). The resistance of fungal growth to the cations Cu, Zn, Ni, Co, Cr, and Cd was significantl y higher at pH 1.0 than at pH 7.0. Such a difference was not observed with Hg, present in the medium at both pH values as electrically silent HgCl2. T he anionic tungstate exhibited the opposite pattern to cationic heavy metal s: The resistance of growth was higher at pH 7.0 than at pH 1.0. A greater growth resistance to heavy metals was correlated with a lower uptake of the se elements, and vice versa; Uptake of heavy metals correlated with a lower resistance of fungal growth to these elements. The results are in agreemen t with the hypothesis that membrane and zeta potentials of the fungus are i mportant factors controlling the uptake of heavy metals and thereby the res istance of growth to these elements: At pH 1.0 positive potentials of funga l hyphae impede the uptake of cationic heavy metals, but facilitate the upt ake of anionic species. At neutral pH values the negative potentials facili tate the uptake of cations, but impede the uptake of anions.