Exploration of cell polymorphisms and factors influencing cell differentiation of Aureobasidium pullulans

Abstract:

[Background] Aureobasidium pullulans belongs to “black yeast” and can synthesize melanin. A. pullulans displays characteristic polymorphic cell types, such as yeast-like cell (YL), swollen cell (SC), chlamydospore (CH), hyphae (HY), monilioid hyphae (MH), septate swollen cell (SSC), meristematic structure (MS). The swollen cell can be further differentiated into chlamydospore, monilioid hyphae, septate swollen cell and meristematic structure. The differentiation of A. pullulans can be regulated by various factors such as pH, temperature and nutritional conditions. [Objective] To study the effects of different oxygen density, temperature, osmotic pressure, pH value and nutrition level on the morphology of A. pullulan cells. [Methods] The microscopic techniques and methylene blue staining were used to observe the effects of different conditions on cell morphology of A. pullulans. [Results] Growth of A. pullulan was not observed under completely anaerobic condition. Under high oxygen condition, the yeast-like cells budded at the early nutrient-rich stage. However, once the nutrient was gradually used up, the yeast-like cells started to form swollen cell and then to chlamydospore. Under low oxygen condition, the yeast-like cell grew into HY through SC at the beginning of incubation when nutrients are rich. The different nutrient concentration had significant effects on the polymorphic differentiation of A. pullulans. Yeast-like cells were the main types of cells in the yeast extract peptone dextrose medium (YPD) medium with high nutrition and optimal ambient conditions. The YL cell differentiated into SC or HY to adapt to or escape the environment in the potato dextrose agar (PDA) medium. The malt extract agar (MEA) medium was nutrient deficient, therefore the SC or HY differentiated into dormant cell CH or MH. The 10% NaCl depressed the growth rate of A. pullulans and inhibited the synthesis of melanin. The effect of 10% KCl or 10% Na2SO4 on the cell differentiation of YL was the same as 10% NaCl, which suggests osmotic stress prevented the differentiation of yeast-like cells into hypha or chlamydospore. The SC was more resistant to high temperature than YL, but less resistant than MS. [Conclusion] Nutrition levels are the key factor regulating cell morphogenesis of A. pullulans.