Abstract
Dimethylsulfide is a volatile organic sulfur compound that provides the largest input of biogenic sulfur from the oceans to the atmosphere, and thence back to land, constituting an important link in the global sulfur cycle. Microorganisms degrading DMS affect fluxes of DMS in the environment, but the underlying metabolic pathways are still poorly understood. Methylophaga thiooxydans is a marine methylotrophic bacterium capable of growth on DMS as sole source of carbon and energy. Using proteomics and transcriptomics we identified genes expressed during growth on dimethylsulfide and methanol to refine our knowledge of the metabolic pathways that are involved in DMS and methanol degradation in this strain. Amongst the most highly expressed genes on DMS were the two methanethiol oxidases driving the oxidation of this reactive and toxic intermediate of DMS metabolism. Growth on DMS also increased expression of the enzymes of the tetrahydrofolate linked pathway of formaldehyde oxidation, in addition to the tetrahydromethanopterin linked pathway. Key enzymes of the inorganic sulfur oxidation pathway included flavocytochrome c sulfide dehydrogenase, sulfide quinone oxidoreductase, and persulfide dioxygenases. A sulP permease was also expressed during growth on DMS. Proteomics and transcriptomics also identified a number of highly expressed proteins and gene products whose function is currently not understood. As the identity of some enzymes of organic and inorganic sulfur metabolism previously detected in Methylophaga has not been characterized at the genetic level yet, highly expressed uncharacterized genes provide new targets for further biochemical and genetic analysis. A pan-genome analysis of six available Methylophaga genomes showed that only two of the six investigated strains, M. thiooxydans and M. sulfidovorans have the gene encoding methanethiol oxidase, suggesting that growth on methylated sulfur compounds of M. aminisulfidivorans is likely to involve different enzymes and metabolic intermediates. Hence, the pathways of DMS-utilization and subsequent C1 and sulfur oxidation are not conserved across Methylophaga isolates that degrade methylated sulfur compounds.
Highlights
Dimethylsulfide is a volatile methylated sulfur compound that has been associated with the ‘smell of the sea’ (Stiefel, 1996) and which plays a crucial role in the global sulfur cycle (Lomans et al, 2002)
Formaldehyde Metabolism Formaldehyde generated through primary metabolism of C1 substrates such as methanol, DMS and methanethiol can be conjugated to tetrahydromethanopterin (H4MPT) by formaldehyde activating enzyme (Fae) for which two coding sequences are found (MDMS009_73 and MDMS009_595)
The comparative proteomics experiment of M. thiooxydans grown either on DMS or methanol showed a great coverage of proteins across several relevant metabolic pathways, including the primary enzymes involved in methanol degradation, methanethiol degradation, functions involved in formaldehyde degradation and assimilation as well as relevant enzymes from central carbon metabolism
Summary
Dimethylsulfide is a volatile methylated sulfur compound that has been associated with the ‘smell of the sea’ (Stiefel, 1996) and which plays a crucial role in the global sulfur cycle (Lomans et al, 2002). Its atmospheric breakdown products (mainly sulfate, sulfur dioxide, and methanesulfonic acid) are important precursors for secondary organic aerosols. These play a role in climate feedbacks by reflecting solar radiation back to space and serving as cloud condensation nuclei (CCN), which support the formation of clouds that reflect further sunlight and may contribute to climate regulation (Charlson et al, 1987; Simó, 2001; Carslaw et al, 2010; Lana et al, 2011). Boden et al (2010) characterized the DMS-degradation pathway in M. thiooxydans based on enzyme assays and analysis of sulfur intermediates and end products and compared it to M. thiooxydans grown on methanol. During growth on DMS, DMS monooxygenase (De Bont et al, 1981; Boden et al, 2010) activity was not detected, and the presence of a methyltransferase (Visscher and Taylor, 1993), which could be responsible for the initial step of DMS degradation, was suggested (Boden et al, 2010) this ‘DMS-methyltransferase’ was not identified
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
