Kerr, James M. (2022) Dissecting the molecular basis of phosphorus cycling in marine phototroph-heterotroph interactions. PhD thesis, University of Warwick.

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Abstract

Marine microbial interactions can be seen as a driver of the biogeochemical cycling of elements, and it is now understood that marine phototrophs are responsible for about half of all carbon dioxide fixation. Primary production by phototrophic picocyanobacteria and picoeukaryotes converts carbon dioxide into dissolved organic matter (DOM). Co-occurring heterotrophic organisms benefit from DOM as a source of carbon and energy, but phototrophs, lacking the necessary secreted enzymes, depend on the re-mineralised inorganic nutrients released by the heterotrophic community. This strategy is particularly important in the vast photic zones of the oligotrophic ocean, where availability of essential nutrients can be limiting.

This project aimed to dissect the molecular mechanisms of this nutrient cycling. Using one-to-one co-cultures combined with mass spectrometric analysis, the change in exoproteomic profile between mono- and co- cultures of R. pomeroyi and 8 model phototrophs revealed generic and species-specific changes. Qualitative analysis of these changes revealed intriguing “phytase-like” secreted proteins in several of the phototrophic cultures, which became the basis for further investigation of phosphorous cycling in particular. One phytaselike protein was overexpressed and purified, showing some de-phosphorylation of different inositol phosphate (InsP) substrates in assay. Gene atlas tools revealed distribution of homologues across P-depleted ocean regions, and cross-domain patterns of expression. In investigating the origin of InsP substrates, and the role they play within marine microbial interactions, cell pellets of the diatoms were found to contain InsP, and an InsP biosynthetic pathway was proposed based on orthologues from the known pathway of A. thaliana.

This research highlights the complexity of the molecular mechanisms underpinning phototroph-heterotroph nutrient cycling, and represents foundational research into the role of phytases, their substrates, and P cycling at large in the marine microenvironment.

Item Type:	Thesis (PhD)
Subjects:	G Geography. Anthropology. Recreation > GC Oceanography Q Science > QH Natural history > QH301 Biology Q Science > QR Microbiology
Library of Congress Subject Headings (LCSH):	Marine microbiology, Photosynthetic bacteria, Cyanobacteria, Seawater -- Organic compound content, Phosphorus cycle (Biogeochemistry)
Official Date:	April 2022
Dates:	Date Event April 2022 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	School of Life Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Christie-Oleza, Joseph Alexander ; Chen, Yin ; Scanlan, David J.
Format of File:	pdf
Extent:	196 pages : illustrations (some colour)
Language:	eng

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