AUTHOR=Zepernick Brittany N. , Niknejad David J. , Stark Gwendolyn F. , Truchon Alexander R. , Martin Robbie M. , Rossignol Karen L. , Paerl Hans W. , Wilhelm Steven W. 

TITLE=Morphological, physiological, and transcriptional responses of the freshwater diatom Fragilaria crotonensis to elevated pH conditions

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.1044464

DOI=10.3389/fmicb.2022.1044464

ISSN=1664-302X

ABSTRACT=<p>Harmful algal blooms (HABs) caused by the toxin-producing cyanobacteria <italic>Microcystis</italic> 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 <italic>Fragilaria crotonensis</italic> 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 <italic>F. crotonensis</italic> 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 <italic>F. crotonensis</italic>. Moreover, we identified a significant upregulation of mobile genetic elements in the <italic>F. crotonensis</italic> genome which appear to be an extreme transcriptional response to this abiotic stress to enhance cellular evolution rates–a process we have termed “<italic>genomic roulette.</italic>” We discuss the ecological and biogeochemical effects high pH conditions impose on fresh waters and suggest a means by which freshwater diatoms such as <italic>F. crotonensis</italic> may evade high pH stress to survive in a “basified” future.</p>