Introduction

Magnesium, calcium, iron, copper, manganese, zinc and often molybdenum are required by fungi for growth. The order approximates to the concentration required in a normal growth medium. Magnesium is required at c. 10 M, while molybdenum need only be at true trace concentrations, namely c. 10 M. The latter element is required by those fungi utilising nitrate (see Chapter 6). Cobolt will be needed by those fungi that synthesise their own vitamin B12 (Fries, 1965), whereas nickel is required by those fungi exhibiting urease activity (Hausinger, 1987). The list might be longer but rigorous evidence for inclusion of other elements is not easy to obtain. Trace contaminants of reagents by a suspected element make it difficult to demonstrate that it is required for growth. Molecular biology and enzyme studies are likely to prove more revealing.

Copper and zinc can be toxic at concentrations higher than those required for growth. Since other multivalent metals can also be toxic, this chapter deals with the avoidance of toxicity. I have refrained, except in certain instances, from listing the role(s) of these various elements in fungi. To give a proper indication of the function of an element requires the provision of biochemical information beyond the scope of this volume.

Transport of multivalent metals (other than iron) across the plasma membrane

Specific systems

At its simplest, uptake of a multivalent metal by a fungus is biphasic; there is an initial rapid phase, which is believed to reflect binding to the wall, followed by a second, slower phase (Figure 11.1)