Data_Sheet_1_Morphological, physiological, and transcriptional responses of the freshwater diatom Fragilaria crotonensis to elevated pH conditions.xlsx

Harmful algal blooms (HABs) caused by the toxin-producing cyanobacteria Microcystis spp., can increase water column pH. While the effect(s) of these basified conditions on the bloom formers are a high research priority, how these pH shifts affect other biota remains understudied. Recently, it was shown these high pH levels decrease growth and Si deposition rates in the freshwater diatom Fragilaria crotonensis and natural Lake Erie (Canada-US) diatom populations. However, the physiological mechanisms and transcriptional responses of diatoms associated with these observations remain to be documented. Here, we examined F. crotonensis with a set of morphological, physiological, and transcriptomic tools to identify cellular responses to high pH. We suggest 2 potential mechanisms that may contribute to morphological and physiological pH effects observed in F. crotonensis. Moreover, we identified a significant upregulation of mobile genetic elements in the F. crotonensis genome which appear to be an extreme transcriptional response to this abiotic stress to enhance cellular evolution rates–a process we have termed “genomic roulette.” We discuss the ecological and biogeochemical effects high pH conditions impose on fresh waters and suggest a means by which freshwater diatoms such as F. crotonensis may evade high pH stress to survive in a “basified” future.

由产毒蓝细菌微囊藻属（Microcystis spp.）引发的有害藻华（Harmful Algal Blooms, HABs）可提升水体pH值。尽管这类碱化环境对藻华优势种的影响是当前研究的重点方向，但pH波动对其他生物类群的影响仍有待深入探究。近期研究证实，高pH环境会抑制淡水硅藻克罗顿脆杆藻（Fragilaria crotonensis）以及北美伊利湖（加拿大-美国界湖）原生硅藻种群的生长与硅沉积速率。然而，与该观测结果相关的硅藻生理机制与转录响应仍未得到系统阐明。本研究通过形态学、生理学与转录组学手段对克罗顿脆杆藻进行分析，以明确其应对高pH环境的细胞响应模式。我们提出了两种潜在机制，以阐释克罗顿脆杆藻在pH胁迫下的形态与生理变化。此外，我们在克罗顿脆杆藻基因组中发现了可移动遗传元件（mobile genetic elements）的显著上调，这似乎是该硅藻应对非生物胁迫的极端转录响应，旨在提升细胞进化速率——我们将这一过程命名为“基因组轮盘赌（genomic roulette）”。本研究还探讨了高pH环境对淡水生态系统与生物地球化学循环的影响，并提出了克罗顿脆杆藻这类淡水硅藻可通过何种策略规避高pH胁迫，以在未来“碱化”的水体环境中存续。