Microbiology Research Center for Sustainability (MiCS), Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
PLoS Biol. 2024 Jul 30;22(7):e3002726. doi: 10.1371/journal.pbio.3002726. eCollection 2024 Jul.
The importance of fungi in ecological systems and pathogenicity hinges on their ability to search for nutrients, substrates, and hosts. Despite this, the question of whether fungal hyphae exhibit chemotropism toward them remains largely unresolved and requires close examination at the cellular level. Here, we designed a microfluidic device to assess hyphal chemotropism of Aspergillus nidulans in response to carbon and nitrogen sources, as well as pH. Within this device, hyphae could determine their growth direction in a two-layer flow with distinct compositions that were adjacent but non-mixing. Under conditions with and without a carbon source, hyphae changed growth direction to remain in the presence of a carbon source, but it was still difficult to distinguish between differences in growth and chemotropism. Although nitrogen sources such as ammonia and nitrate are important for growth, the hyphae indicated negative chemotropism to avoid them depending on the specific transporters. This fungus grows equally well at the colony level in the pH range of 4 to 9, but the hyphae exhibited chemotropism to acidic pH. The proton pump PmaA is vital for the chemotropism to acid pH, while the master regulatory for pH adaptation PacC is not involved, suggesting that chemotropism and adaptive growth via gene expression regulation are distinct regulatory mechanisms. Despite various plasma membrane transporters are distributed across membranes except at the hyphal tip, the control of growth direction occurs at the tip. Finally, we explored the mechanisms linking these two phenomena, tip growth and chemotropism.
真菌在生态系统中的重要性及其致病性取决于它们寻找营养物质、基质和宿主的能力。尽管如此，真菌菌丝是否表现出对它们的化学趋性的问题在很大程度上仍未得到解决，需要在细胞水平上进行仔细检查。在这里，我们设计了一种微流控装置来评估 Aspergillus nidulans 的菌丝对碳和氮源以及 pH 的化学趋性。在该装置中，菌丝可以在具有不同组成的两层流中确定其生长方向，这两层流是相邻但不混合的。在有和没有碳源的条件下，菌丝改变生长方向以保持在碳源存在的情况下，但仍然很难区分生长和化学趋性之间的差异。尽管氨和硝酸盐等氮源对生长很重要，但菌丝根据特定的转运蛋白表现出对它们的负化学趋性。这种真菌在 4 到 9 的 pH 范围内在菌落水平上同样生长良好，但菌丝表现出对酸性 pH 的化学趋性。质子泵 PmaA 对酸 pH 的化学趋性至关重要，而 pH 适应的主调节因子 PacC 不参与，这表明化学趋性和通过基因表达调节的适应性生长是不同的调节机制。尽管各种质膜转运蛋白除了在菌丝尖端外都分布在膜上，但生长方向的控制发生在尖端。最后，我们探讨了将这两种现象（尖端生长和化学趋性）联系起来的机制。
