Adaptation of Fungi to Metal Toxicants

Abstract

Since toxic concentrations of metals may have existed on earth only rarely, the ability of organisms to adapt to metal toxicants might not have evolved, but rather may be adventitious. For example, let it be assumed that the toxic effect of a metal is reduced when one of the normal physiological activities is much heightened. If a mutant occurs which is "abnormally" high in that particular activity, then the mutant will be selected in the presence of that metal, and the organism will be regarded as having adaptability to the metal. The high activity of hydrogen sulfide production in yeast seems to be such a case. Cases of physiological adaptation also may be viewed in a similar way. With fungi, long training periods are needed for the development of clearly observable metal resistance in most cases so far reported, and studies on this phenomenon seem to be attended by many difficulties. But many interesting and important problems remain to be studied, such as whether (or how) nuclei of a certain nature are sorted out when multinucleate coenocytic fungi grow under effect of a toxicant; whether cytoplasmic determinants are involved in the adaptation; why characteristics such as pathogenicity and capacity for sexual combination are impaired as resistance is acquired, etc. The nature of metal toxicity has not yet been well elucidated. It might then be supposed that it is too early to study the mechanism of resistance to metals. What can be studied, however, is whether metal ions are detoxified by some substance or whether permeability to metals is lower, although determinations free of objections are not easy to make. When the metabolic pathways which are specifically developed in resistant cells are studied in parallel with the reaction steps which, in sensitive cells, are most sensitive to the metal in question, there will be a way to elucidate the metal toxicity hand in hand with the resistance mechanism. There is a bibliography of 124 references.