Natural-abundance 3C Nuclear Magnetic Resonance Studies on the Internal Solutes of Xerophilic Fungi

Natural-abundance 3C nuclear magnetic resonance spectroscopy was used to study the patterns of accumulation of osmotically active internal solutes in five different fungi. Four xerophilic fungi (Penicillium janczewskii, Eurotium chevalieri, Xeromyces bisporus and Wallemia sebi), and one non-xerophilic fungal species ( P . digitatum) were grown at three different water activities (a,) on media containing sorbitol, glucose/fructose or NaCl as the controlling solute. Under all conditions studied, the major internal solutes detected in aqueous ethanol extracts of these fungi were simple polyhydric alcohols : glycerol, erythritol, arabitol and mannitol. The most important osmoregulatory solute accumulated by all species was glycerol. On the sorbitol and the glucose/fructose media, all five fungi were able to accumulate glycerol. However, when NaCl was used to control a,, only one species, W. sebi, was able to accumulate glycerol below 0.92 a,, Significant quantities of the controlling solutes were also present in the extracts. When intact mycelia of P . janczewskii were examined by NMR, resonances of all the major internal solutes were clearly discernible, although they were not as well resolved as those from the fungal extracts. Relaxation measurements showed that the solutes were relatively mobile inside the cells.