Diatoms and Calcium

: Deciphering Responses to Environmental Signals at the Molecular Level

Abstract

Diatoms are an important group of microalgae acting as primary producers in marine and freshwater environments. Little is known about the mechanisms that diatoms use to detect and respond to environmental conditions. Calcium (Ca2+) signalling is used ubiquitously in eukaryotic organisms to perceive and respond to environmental stimuli. We aimed to investigate diatom Ca2+ signalling mechanisms in greater detail.

We explored the Ca2+ ion channel toolkit of both pennate and centric diatom species, to determine evolutionary gains and losses of different Ca2+ channels within the stramenopile lineage. We used a novel ratiometric genetically encoded Ca2+ indicator to discern the involvement of Ca2+ signalling in the responses of the model diatom Phaeodactylum tricornutum to environmental factors. Diatom cell density has significant effects on cell physiology, which links to the formation and demise of diatom blooms. We therefore investigated how cell density affects Ca2+-dependent signalling mechanisms. Our findings revealed that P. tricornutum responds to compounds present in the surrounding media, initiating major changes in Ca2+ signalling based on local cell density.

We also investigated glutamate-induced Ca2+ signalling in P. tricornutum. Glutamate signalling is used by multicellular eukaryotes for cell-cell communication. We identified a single novel glutamate receptor (GLR) gene in P. tricornutum. We also found that glutamate causes a transient Ca2+ signal in P. tricornutum, which was suppressed by the simultaneous perfusion of the diatom-derived compound domoic acid. The results indicate that diatoms may use glutamate signalling to perceive stress and wounding in neighbouring cells.

As local cell density and cellular stress levels are continuously fluctuating, our findings highlight the complexity of diatom Ca2+ signalling mechanisms, and indicate that diatoms may function not merely as individual cells but as an interconnected network. Additionally, an enhanced understanding of these mechanisms will have applications in biotechnology, where diatoms are utilised to produce valuable products.

Date of Award	4 Feb 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Glen L. Wheeler (Supervisor)