The role of microbial rhodopsins in the evolution and adaptation of a marine diatom

Deng, Longji (2024) The role of microbial rhodopsins in the evolution and adaptation of a marine diatom. Doctoral thesis, University of East Anglia.

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Abstract

Microbial rhodopsins have been identified in bacteria, archaea, viruses, and eukaryotic phytoplankton, but their in-vivo function in the latter group has largely remained elusive. The discovery of two variants (FR1/FR2) of xanthorhodopsin in 2008, as part of the Fragilariopsis cylindrus genome project, initiated focused research to explore the role of these proton-pumping and retinal-binding membrane proteins in key oceanic primary producers. This thesis is one such project, aimed at uncovering how microbial rhodopsins in the polar diatom Fragilariopsis cylindrus contribute to the success of these primary producers, particularly in polar regions like the Southern Ocean.

Using a combination of bioinformatics, molecular biology, and physiological experiments, this thesis reveals how rhodopsins in F. cylindrus enhance diatom growth, especially in the iron-limited Southern Ocean, a high-nutrient, lowchlorophyll (HNLC) region. The findings indicate that the xanthorhodopsin variant FR1 acts as a light-driven proton pump with significant activity in cold, iron-limited environments, typical of the Southern Ocean. This suggests that microbial rhodopsins provide an additional energy acquisition pathway, supplementing photosynthesis when iron is scarce.

Furthermore, a genetically modified Thalassiosira pseudonana strain expressing FR1 exhibited enhanced growth and photosynthetic efficiency under iron-limited conditions, highlighting the adaptive advantage provided by these microbial rhodopsins. The expression of FR1 in the heterotrophic diatom Nitzschia putrida further demonstrated that, even in the absence of photosynthetic electron transport, FR1 can function as an alternative “photosystem,” allowing heterotrophic organisms to harness light for proton generation, supporting ATP synthesis or aiding in nutrient acquisition for growth.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Depositing User:	Chris White
Date Deposited:	01 Dec 2025 15:13
Last Modified:	01 Dec 2025 15:13
URI:	https://ueaeprints.uea.ac.uk/id/eprint/101171
DOI:

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