Microbial degradation of dimethylsulfoxide in the marine environment

Dimethylsulfoxide (DMSO) is a chemical with a wide range of applications. It is a widely used solvent, for instance in pharmaceutical applications, and a waste product of the paper milling industry. It also occurs naturally in a range of fruits, like raspberries, and vegetables. However, DMSO is also a compound that is part of the natural sulphur cycle. Sulphur is an essential element for all life, and in its organic form is a component of all proteins such as the amino acids cysteine and methionine. DMSO is an organic sulphur compound found everywhere in our oceans, and is produced by a number of natural biological and chemical processes.

DMSO is important because it is both a source and a sink for a climate-cooling gas called dimethyl sulfide (DMS). DMS is a component of the smell of the seaside. Around 300 million tons of DMS are made each year by marine microorganisms. Some of this DMS is released into the atmosphere above the oceans, where it reacts in air to compounds that seed clouds, which is suggested influences weather and climate. When it rains, sulphur compounds are deposited back into the soils of our continents. However the majority of the DMS formed in the oceans is thought not to be released to the atmosphere, but rather to be converted to DMSO, and thus stays in seawater. However what happens to this DMSO largely remains a mystery, but it has been suggested that it can be converted back to DMS, and thus be a source for climatically relevant sulphur emissions to the atmosphere. What we do know is that DMSO is commonly the most abundant organic sulphur compound in the oceans, and represents a major pool of the essential life elements sulphur and carbon.

The research to be carried out in this proposal is focused on firstly finding out what happens to DMSO in seawater. We have some preliminary evidence, found using radiolabelled DMSO as a tracer, that it is degraded by microorganisms who both incorporate its carbon into their biomass for growth purposes, and degrade it to carbon dioxide. However we also think that perhaps other microbes could transfer DMSO back to DMS, and even use its sulphur as an essential element. Therefore in this proposal we have designed a series of different tracer experiments to find out which processes occur in our seas, how important they are and how fast they happen. We will also put names to the microbes using DMSO, and find out which metabolic pathways are involved. We will study these microbial DMSO transformations in the English Channel at a station called L4. This station is sampled weekly as part of the Western Channel Observatory which is coordinated by Plymouth Marine Laboratory. This is a long-standing time series site for which data on phytoplankton diversity, abundance, temperature, nutrient dynamics and bacterial diversity are also measured and will be made freely available to this project (http://www.westernchannelobservatory.org.uk).

Given the important role of DMSO and its related compound DMS, identifying the populations and pathways of DMSO removal from seawater will provide key information that will improve our future understanding of the complex sulphur cycle and how it influences our climate.

The main motivation for the proposed research is to address a question of fundamental importance for understanding the marine sulfur cycle - which microbes are responsible for degrading the abundant organosulfur compound dimethylsulfoxide and which mechanisms do they use to do that in the marine environment?

Due to its intimate link to dimethylsulfide, a climate cooling gas, and its potential to serve as a major DMS source, the degradation of DMSO in the oceans will be of general interest to the public who are more and more interested in the ways our climate is regulated. We will provide information about the project context and key results via dedicated websites on the PML and Warwick University pages that are suitable for lay readers.

Due to DMSO being an industrial solvent, the work described here will deliver important information regarding the degradation of a high volume chemical that is used in a wide array of industrial applications (paint strippers, solvent for agrochemicals, pharmaceutical delivery, polymer production, etc); crucially, we expect to learn about the degradation of DMSO under aerobic conditions and pathways that may not give rise to DMS, a malodorous compound that can cause nuisance smells, for instance in waste water treatment plants. While there is no immediate application of our findings to waste water treatment, we do intend to engage with water companies to gauge the level of interest in biotechnology that aims to degrade DMSO in waste water without generation of nuisance smells that disturb the public. Potentially, there may be interest in DMSO degrading organisms in treatment of wastes from DMSO producing industrial companies. If there is interest from industry we will pursue further research in the future to develop relevant biotechnology.

Another important aspect of the project is the further development of targeted metagenomics approaches based on stable isotope probing in combination with high throughput next generation sequencing approaches to help chart unknown metabolic genes in microorganisms. The wider application and future exploitation of metagenomic approaches to identify and harness microbial enzymes for the field of synthetic biology and the continued development of systems ecology approaches relies on efficient bioinformatic and statistical processing of the large sequence data sets generated by next generation sequencing methods which we will apply to our data. This will help the future competitiveness of the UK research base in a challenging research field that is likely to be a cornerstone of the future UK bioeconomy.