The interplay of dimethylsulfioniopropionate and glycine betaine production in marine cyanobacteria

Walsham, Keanu Stuart (2023) The interplay of dimethylsulfioniopropionate and glycine betaine production in marine cyanobacteria. Doctoral thesis, University of East Anglia.

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Abstract

Dimethylsulfoniopropionate (DMSP) is a key chemical in the global sulfur cycle and the main source of dimethylsulfide (DMS), a global cooling gas. DMSP is hypothesized to have several stress protection roles and is accumulated by a broad range of organisms. Glycine betaine (GB), a nitrogenous chemical found in every domain of life, has a similar role. Production of DMSP in cyanobacteria, an abundant phylum of oxygenic photosynthetic prokaryotes found in nearly environment on Earth, has only been investigated in a few species and the enzymes involved in its production have not been identified. In contrast, GB synthesis in cyanobacteria has been more thoroughly investigated and the proteins involved in this process have been elucidated. In this study, we identified a novel MTHB SAM-dependent methyltransferase, termed DsyC, which is found in many cyanobacteria including Prochlorococcus spp., Synechococcus spp. and Trichodesmium erythraeum IMS101. Interestingly, this protein also methylates intermediates of the GB methylation pathway and HB methylation pathway, demonstrating its role as a multifunctional DMSP-linked methyltransferase. Axenic Synechococcus spp and Prochlorococcus spp. were shown to produce DMSP but there was no relationship between DMSP and GB production under nitrogen limitation. This suggests that marine cyanobacterial DMSP production could be a major contributor to the global pool. Additionally, DMSP production was seen in species not containing DsyC, suggesting that other uncharacterised methyltransferases may catalyse this reaction. Investigation of an intertidal microbial mat demonstrated the presence of DsyC containing species, including cyanobacteria such as Coleofasciculus chthonoplastes and Lyngbya aestuarii. Together with algae containing another novel MTHB SAM-dependent methyltransferase, DSYU, this environment had between 400 – 700 μM DMSP g-1 sediment. Given the abundance of global saltmarshes, many dominated by cyanobacteria and algae, this suggests that these ecosystems could also be major contributors to DMSP production Together, these results demonstrate the importance of DsyC in DMSP synthesis, the role cyanobacteria play in global production of DMSP and in modulating the Earth’s climate.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Biological Sciences
Depositing User:	Nicola Veasy
Date Deposited:	02 Jul 2024 08:51
Last Modified:	02 Jul 2024 08:51
URI:	https://ueaeprints.uea.ac.uk/id/eprint/95745
DOI:

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