Characterisation of DMSP synthesis in marine bacteria via the methylation pathway

Cowles, Kasha (2023) Characterisation of DMSP synthesis in marine bacteria via the methylation pathway. Doctoral thesis, University of East Anglia.

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Dimethylsulfoniopropionate (DMSP) is one of the Earth’s most abundant organosulfur molecules, with approximately 9 billion tonnes being produced annually, and is the primary cause of the release of the climate-active gas dimethylsulfide (DMS). The molecule provides many benefits to the organisms with the ability to synthesise DMSP and many that cannot actively assimilate it from the environment. Although bacteria have been well-documented as DMSP degraders, they have only recently been identified as DMSP producers. The saltmarsh environment is a hotspot for DMSP production, with DMSP concentrations in the Stiffkey saltmarsh sediment (77.1 ± 15.0 nmol DMSP g-1) much higher than the overlying pool water (0.4 ± 0.1 nmol DMSP ml-1). Approximately 25 % of the bacteria isolated from the sediment could produce DMSP, which could be increased following enrichment conditions to 77 %. Whilst most isolates contained the bacterial DMSP-synthesis reporter gene, dsyB, several did not (Alteromonas, Marinobacter, and Novosphingobium). Novosphingobium was an interesting strain, as incubation with intermediates from the three DMSP synthesis pathways revealed that Novosphingobium only produced DMSP in the presence of intermediates from the methylation pathway. Upon further research, a bacterial methionine methyltransferase was identified and termed ‘mmtN’, responsible for the methylation of methionine, producing S-methylmethionine (SMM). While SMM is a process found in all flowering plants, this is the first instance observed in bacteria. Upon further analysis, mmtN is found within a diverse range of bacteria and has been demonstrated as functional in those tested. An mmtN disruption mutant created in T. profundimaris removed the ability of the strain to produce DMSP. However, DMSP synthesis was reinstated when the mutant strain was complemented with mmtN from Novosphingobium. The results presented in this thesis suggest that bacteria have more than one method for producing DMSP and details the discovery of the second DMSP synthesis gene.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Chris White
Date Deposited: 03 Jul 2024 10:37
Last Modified: 03 Jul 2024 10:37


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