Inter- and intra-species heterogeneity in germination of Aspergillus conidia

Abstract

Aspergilli are among the most abundant fungi worldwide. They degrade organic material and can be pathogens of plants and animals. Aspergilli spread by forming high numbers of conidia. Germination of these stress resistant asexual spores is characterized by a swelling and a germ tube stage. Here, we show that conidia of Aspergillus niger, Aspergillus oryzae, Aspergillus clavatus, Aspergillus nidulans and Aspergillus terreus show different swelling and germ tube formation dynamics in pure water or in water supplemented with (in)organic nutrients. Apart from inter-species heterogeneity, intra-species heterogeneity was observed within spore populations of the aspergilli except for A. terreus. Sub-populations of conidia differing in size and/or contrast showed different swelling and germ tube formation dynamics. Together, data imply that aspergilli differ in their competitive potential depending on the substrate. Moreover, results suggest that intra-species heterogeneity provides a bet hedging mechanism to optimize survival of aspergilli.

Keywords: Amino acids; Aspergillus; Conidia; Fungus; Germination; Swelling.

Fig. 1

Heat map of normalized P_max of swelling and germ tube formation in response to amino acids taken up in PS (NaPO4 buffer, pH 6, MgSO4). To this end, the P_max of the medium containing the amino acid was subtracted from the P_max of the PS medium. Tyrosine was excluded from the data set because of the resulting low pH of the medium. Hierarchical clustering shows that low, intermediate and high swelling and germ tube inducing amino acids can be distinguished. Moreover, it is shown that clustering of the aspergilli based on swelling and germ tube formation does not follow phylogeny

Fig. 2

Scatter plots showing the 15% small and 15% large sized sub-populations (left) and 15% low and 15% high contrast sub-populations (right) of conida of representative replicates of A. niger (A), A. oryzae (B), A. clavatus (C), A. nidulans (D), and A. terreus (E)