DMSP Production in Earth’s Highest Producers

Hanwell, Libby (2024) DMSP Production in Earth’s Highest Producers. Doctoral thesis, University of East Anglia.

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Abstract

DMSP (dimethylsulphoniopropionate) plays an essential role in the global sulphur cycle and is the main progenitor of the climate active gas DMS (dimethylsulphide). Dinoflagellates are some of Earth’s highest producers of DMSP, exceeding 425 mM/cell volume, using the molecule as an antistress compound and nutrient source. Dinoflagellates are predicted to utilise the transamination pathway for DMSP synthesis, with the key DSYB enzyme identified in most dinoflagellate species. Despite this, Crypthecodinium cohnii, a heterotroph known in industry for its docosahexaenoic acid (DHA) production, is reported to synthesise DMSP by a poorly characterised decarboxylation pathway. Several dinoflagellates are also known to lyse DMSP to the climate active gas dimethylsulphide (DMS) thus understanding the how, who and where of DMS/P synthesis is important to inform global climate models and the sulphur budget as a whole.

Here I identified 4 functional DSYB enzymes in C. cohnii, predicted to be involved in the synthesis of DMSP. Interestingly, two of these enzymes were able to utilise the predicted decarboxylation intermediate methylmercaptopropionate (MMPA) as a substrate in addition to 4-methylthio-2-oxobutyrate (MTHB) of the transamination pathway. Furthermore, 8 candidate methionine decarboxylase enzymes were identified via activity tracking purification and proteomics, but further work is needed to determine if any of these candidate enzymes were the elusive and key initial enzyme of the decarboxylation pathway.

C. cohnii was found to produce more DMSP under conditions of raised salinity and photoooxidative stress. Transcriptomics and proteomics were also utilised to identify genes/proteins regulated in the same way as DMSP. However, neither DSYB gene transcripts or proteins were upregulated with DMSP under these conditions, and no further candidate DMSP synthesis enzymes were identified. Nevertheless, my generation of extensive transcriptomic, proteomic, and zwitterionic metabolomic datasets here will be useful in further research in lieu of a C. cohnii genome. Crypthecodinium cohnii was shown to have significant DMSP lysis activity and contain four Alma-family DMSP lyase enzymes. Three of these lyases contained a double Alma domain architecture, not seen previously in any functionally characterised Alma enzyme. The transcription of all 4 Cryp-Alma genes were regulated by salinity, in fitting with DMSP lysis potentially having a role in promoting growth through enhancing the bioavailability of DMSP’s carbon-containing acrylic acid moiety, particularly under osmotic stress.

This thesis provides novel insights into DMSP synthesis enzymes and cycling in Crypthecodinium cohnii and regulation of these processes, helping to unravel the puzzle of DMSP metabolism in this dinoflagellate. Specifically, through identification of functional DMSP synthesis and lyase enzymes, and investigating DMS/P production under osmotic and photooxidative stress and what impact these stressors have on the transcriptome, proteome and zwitterionic metabolome of C. cohnii. In the future, the hope is the molecular findings from this work can help build contemporary climate models related to sulphur cycling because of the identification of functional DMSP catabolism enzymes from this globally distributed, high DMSP producing dinoflagellate.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Biological Sciences
Depositing User:	Chris White
Date Deposited:	09 Jun 2025 10:22
Last Modified:	09 Jun 2025 10:22
URI:	https://ueaeprints.uea.ac.uk/id/eprint/99404
DOI:

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