Intracellular trehalase activity is required for development, germination and heat-stress resistance of Aspergillus niger conidia

The disaccharide trehalose is known as a stress protectant in several kinds of organisms, including fungi, where it is a major carbohydrate in resting structures, e.g. asexual conidia. The gene encoding the enzyme responsible for degradation of intracellular trehalose, treB, was deleted and the phenotype was analyzed in terms of morphology, trehalose content during conidial outgrowth and stress tolerance. The mutant conidiophores produced fewer and less viable spores, and during early stages of germination the internal levels of trehalose were higher compared to the wild type. When subjecting the mutant to various stresses (weak acid and salt), no increased sensitivity could be observed, but in line with previous observations, e.g. in Aspergillus nidulans, Aspergillus niger ΔtreB spores in a very early stage of germination were less sensitive to heat stress. In contrast, when subjecting resting spores to 55 °C, an intact treB gene was essential for survival. This finding suggests that trehalose mobilization is required to facilitate cell recovery after heat-induced damage.