Heavy Metal Resistance of the Extreme Acidotolerant Filamentous Fungus Bispora sp |
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Authors: | Gimmler H Jesus J Greiser A |
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Institution: | Julius-von-Sachs-Institut für Biowissenschaften, Universit?t Würzburg, Germany. |
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Abstract: | To obtain information on the importance of membrane and zeta potentials as repelling or facilitating forces during the uptake
of cationic trace elements, 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 elements 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 in the medium
in anionic form (sulfate, chloride) showed the opposite pattern to cations: Contents were higher at pH 1.0 than at pH 7.0.
Minerals present at pH 1.0 predominantly in the electrical neutral, protonated form (phosphate, 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 significantly 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. The anionic tungstate exhibited the opposite pattern to cationic heavy metals: 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 these elements, and
vice versa; Uptake of heavy metals correlated with a lower resistance of fungal growth to these elements. The results are in agreement
with the hypothesis that membrane and zeta potentials of the fungus are important factors controlling the uptake of heavy
metals and thereby the resistance of growth to these elements: At pH 1.0 positive potentials of fungal hyphae impede the uptake
of cationic heavy metals, but facilitate the uptake of anionic species. At neutral pH values the negative potentials facilitate
the uptake of cations, but impede the uptake of anions. |
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Keywords: | Acid resistance Bispora sp Dunaliella acidophila heavy metals membrane potential zeta potential |
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