Aqueous Two-Phase System (ATPS)-Based Spore Isolation in Schizosaccharomyces pombe Requires Isp3-Dependent Surface Hydrophobicity

Abstract

The fission yeast Schizosaccharomyces pombe is a valuable unicellular model organism that proliferates predominantly in the haploid state. Under nitrogen starvation, sexual reproduction occurs, resulting in the formation of a diploid zygote and subsequent meiosis, producing four haploid ascospores. The genetic tractability of yeast, particularly, its ability to produce offspring through sexual reproduction, makes it a widely used model organism. Spores also serve as a model for dormant cells. In this study, I present a highly efficient and low-cost method for purifying S. pombe spores using an aqueous two-phase system (ATPS). Using polyethylene glycol (PEG)-salt (e.g., phosphate)-based ATPS, free spores were found to partition exclusively into the upper (PEG-rich) phase. In contrast, spores lacking Isp3, which forms the outermost spore wall layer, partitioned into the lower (salt-rich) phase, like vegetative cells. This suggests that the Isp3 layer imparts hydrophobicity to the spore surface, facilitating efficient separation in ATPS. This unique surface property may also reflect differences in ecological adaptation and spore dispersal strategies between S. pombe and other fission yeast species.