Penicillium rubens germination on desiccated and nutrient-depleted conditions depends on the water activity during sporogenesis

Abstract

Fungal growth often appears in a surrounding where water and nutrients are scarce. The impact of this environment during sporogenesis on subsequent growth is often neglected. This study investigates the effect of water availability during sporogenesis on subsequent early growth. Therefore, a carbon-depleted substrate was constructed. Humidity is then the only parameter of interest. The water conditions during sporogenesis, and during subsequent growth, were varied. This is a stressing environment: no carbon source is present, and water provided solely via the vapour. The lag time, t_l, and initial growth rate, μ_fp, of the germ tubes were monitored. The effect of a_w history on germination and initial growth depends on the RH of the environment. Only at low RH do spores produced at low a_w have a smaller t_l and higher μ_fp compared to those grown at high a_w. This result was remarkably pronounced when the substrate was also made hydrophobic: growth only occurred when spores were developed at low a_w and placed in high RH. Spores grown on lowered a_w attract more water. It is hypothesized that this attraction affects subsequent growth behaviour, and is the reason why growth on hydrophobic glass only prevails in the condition of high RH and lowered a_w history. We demonstrate the influence of cultivation conditions on germination, which becomes more pronounced in a more desiccated environment.

Keywords: Germination time; Hydrophobic glass; Hyphal growth rate; Relative humidity; Sporogenesis conditions.