Phenotypic plasticity in Aureobasidium pullulans isolates

Phenotypic plasticity is the ability of organisms to change phenotypes in response to environmental selection pressures. With the characteristic of no mobility, the ability to respond to fluctuating environments plays a crucial role in the evolutionary success of microorganisms. Aureobasidium pullulans (de Bary) Arnaud is a yeast-like fungus found widespread and it is notable for its morphological variance. However, mechanisms through which A. pullulans adapts in different ecological niches remain unknown. The present study, phenotypic plasticity of A. pullulans was investigated. The traits of A. pullulans were examined under different environmental conditions. For cell colonization, indole-3-acetic acid (IAA) production is a strategy of interference competition. We observed that IAA production increased with the increasing concentration of the exogenous precursor tryptophan. Regarding nutrient acquisition, the production of siderophores, which scavenge ferrous ions, increased when the concentration of ferrous ions was low and vice versa. This suggests the role of siderophore-mediated antagonism of competitors (exploitative competition). Regarding the phosphate-solubilizing ability used for acquiring phosphorous, strains could more efficiently dissolve dicalcium phosphate and calcium triphosphate hydroxide compared with phosphorite. However, all A. pullulans strains used in this study could dissolve all the three types of phosphates. We also tested their abilities to protect themsleves against environmental pressures. The biofilm formation ability, which is useful in protection and fixation, was higher at 19°C and 28°C but lower at 37°C. The antioxidant capacitydecreased with increasing salinity. The results of this study demonstrated the phenotypic plasticity and genetic variation of A. pullulans and suggested that both play important roles in the adaptation of A. pullulans in fluctuating environments.