Cell morphological plasticity in response to substrate availability of a cosmopolitan polymorphic yeast from the open ocean

Polymorphic yeasts can switch between unicellular division and multicellular filamentous growth. Although prevalent in aquatic ecosystems, such as the open ocean, we have a limited understanding of the controlling factors on their morphological variation in an aquatic ecology context. Here we show that substrate concentration regulates cell morphogenesis in a cosmopolitan polymorphic yeast, <i>Aureobasidium pullulans</i>, isolated from the pelagic open ocean and analyzed in liquid batch culture. Filamentous cell development was triggered only under high initial substrate conditions, suggesting that hyphal growth could be more advantageous under eutrophic conditions and may influence pelagic fungal interactions with particulate organic matter. Filamentous growth proportionally declined before the exhaustion of substrate and before budding yeast-type cell division entered stationary phase, possibly modulated by quorum sensing as previously evidenced in other polymorphic yeasts. We also found that budding yeast-type unicells decreased in size and became more elongated in shape in response to substrate depletion, resulting in higher cell surface area to volume ratios, which could affect yeast dispersal and/or provide a nutrient uptake advantage under oligotrophic conditions. Our results demonstrate resource-responsive morphological plasticity in a marine-derived polymorphic yeast, providing mechanistic insight into the ability of fungi to survive fluctuating environmental conditions such as in the open ocean.

多态酵母可在单细胞分裂与多细胞丝状生长之间实现切换。尽管这类酵母广泛分布于开放海洋等水生生态系统中，但目前学界对其在水生生态背景下形态变异的调控机制仍缺乏深入认知。本研究针对一株分离自远洋开放海洋、经液体分批培养（liquid batch culture）分析的广布多态酵母——出芽短梗霉（Aureobasidium pullulans）展开研究，发现底物浓度可调控其细胞形态发生。仅在高初始底物浓度条件下，方可诱导丝状细胞发育，这表明菌丝生长在富营养条件下更具竞争优势，且可能会影响远洋真菌与颗粒有机物之间的相互作用。丝状生长比例在底物耗尽前、出芽酵母型细胞分裂进入稳定期前出现成比例下降，这一调控过程可能由群体感应（quorum sensing）介导——该机制已在其他多态酵母中得到验证。研究同时发现，随着底物耗尽，出芽酵母型单细胞的体积减小、形态更趋细长，导致细胞表面积与体积比升高，这或可影响酵母的扩散能力，或在寡营养条件下为其带来养分摄取的竞争优势。本研究结果证实了一株海洋来源多态酵母的资源响应型形态可塑性，为解析真菌在开放海洋等波动环境中的生存适配能力提供了机制层面的新见解。