- Signalling in microbial foodwebs
- Ecology of traces gases in the infochemistry of phytoplankton
- Chemodetection of DMS in microzooplankton, copepods and krill
- Production of biogenic trace gases under future CO2 levels
- Metabolic pathways for DMSP-dependent DMS-production
- Role of dimethylsulphoniopropionate (DMSP) and related compounds in the stress-physiology of zooxanthellae-cnidarian symbioses
- Production of dimethyl sulphide (DMS) and isoprene in coral reef ecosystems
- Production of ethene (ethylene) in marine algae and its possible function as an infochemical
My research interest is the production of biogenic trace gases in marine environments. Marine algae are a source of volatile organohalogens (e.g. methyl iodide), non-methane hydrocarbons (e.g. ethene, isoprene) and the sulphur gas dimethyl sulphide (DMS). These compounds can affect atmospheric processes after sea-to-air transfer. Over the last 30 years, much research has focused on the production of DMS. This volatile compound plays a major role in the biogeochemical cycling of sulphur, influences atmospheric acidity and is thought to affect climate through the production of cloud condensation nuclei. The precursor of DMS is dimethylsulphoniopropionate (DMSP), a compatible solute found in the cells of some types of marine phytoplankton and seaweeds, but the conversion of DMSP to DMS occurs via a network of processes within the marine microbial foodweb.
The ecology of traces gases in the infochemistry of phytoplankton
The production of DMS is greatly increased by biological interactions including grazing. Since the background concentrations of DMS are low (nanomolar range), grazing by herbivorous flagellates and ciliates results in distinct gas signatures that could provide a directional cue to carnivorous mesozooplankton including copepods and krill. Potentially, DMS and other gases can mediate the tritrophic interactions between small phytoplankton, herbivorous protists and larger zooplankton. Analogous interactions between plants, herbivores and carnivores are well described for terrestrial examples, where the production of trace gases by the plant indirectly reduces the grazing pressure from herbivores. It is likely that such interactions exist in the pelagic realm but this has not been demonstrated in any aquatic environment.
Chemodetection of DMS in microzooplankton, copepods and krill
We use behavioural filming, microcapillary assays and particle-image velocimetry (PIV) to investigate the swimming behaviour of microzooplankton, copepods and krill when exposed to gradients of DMS and DMSP. Our work indicted that copepods and krill have the sensory capability to perceive gradients of DMS. This suggests that DMS is much more than a trace gas with climatic consequences but that it is an infochemical that affects the behaviour of zooplankton and could alter the ecology of predator-prey relationships.
Metabolic pathways for DMSP-dependent DMS-production
Despite its overall importance for climate, the production of DMS is still somewhat of a mystery. Our recent work focussed on the production of DMS in bacteria where we identified a novel pathway for DMSP-dependent DMS-production. Previous work on axenic phytoplankton cultures demonstrated that algae are capable of direct DMS production, however, molecular genetic evidence for this is still lacking. We are now using proteomic and transgenic approaches to unravel the molecular details of DMS release in the coccolithophore Emiliania huxleyi.
The ecophysiology of biogenic trace gases under future CO2 levels
Many of the marine trace gases affect climate through the formation of cloud condensation nuclei in the atmosphere or the destruction of tropospheric ozone. Man’s unwavering reliance on the combustion of fossil fuels, combined with activities including deforestation and cement production, has resulted in ever-increasing atmospheric CO2 concentrations. Part of this additional CO2 dissolves in the surface oceans where it leads to ocean acidification. The effect of ocean acidification on trace gas production is not well understood and we participated in recent field-mesocosm experiments that provided a first insight into the role of future CO2 levels on the concentrations of DMS and organohalogens. We are currently participating in turbidostat-mesocosm experiments that study acclimated cultures of Emiliania huxleyi under present and future CO2 levels.
The role of DMSP and related compounds in the stress-physiology of zooxanthellae-cnidarian symbioses
Coral reefs are hotspots for the production of DMSP and DMS. Virtually all of this is produced by autotrophic dinoflagellates from the genus Symbiodinium (zooxanthellae) that live symbiotically with many marine invertebrates including sea anemones and corals. The exact biological reason for DMSP and DMS production is unknown but they may assist with the scavenging of harmful Reactive Oxygen Species (ROS), so may function as antioxidants in algae. Indeed, our studies with isolated Symbiodinium suggest a close link between DMS production and temperature- and light-induced oxidative stress. Some Symbiodinium genotypes are better adapted to high oxidative stress than others. Is their ability to produce DMS-antioxidants related to the susceptibility of Symbiodinium-coral relationships to stress?
Production of dimethyl sulphide (DMS) and isoprene in coral reef ecosystems
We recently started adapting a Fast Isoprene Sensor (FIS) for our work on aquatic samples. This sensor is being used in the field and in the laboratory in combination with the conventional gas chromatographic techniques to monitor production of DMS and isoprene in various environments including temperate estuaries and tropical coral reefs. Our first field test at a coral reef in Indonesia was successful and revealed specific patterns of isoprene release from various coral species. In higher plants, isoprene is produced in response to thermal stress and likely assists with membrane functioning. Further work will focus on the dynamics of isoprene release under various environmental conditions.
Production of ethene (ethylene) in marine algae and its possible function as an infochemical
Ethene is a gaseous plant “hormone” that is of critical importance for the flower and fruit development in higher plants. We demonstrated that the marine seaweed Ulva (Enteromorpha) intestinalis produces ethene via the same metabolic pathway described for terrestrial plants. Physiological experiments showed that light stress can greatly enhance the co-release of ethene with DMS. However, whether ethene plays a role in the light acclimation process, for example via the induction of de-novo synthesis of protective pigments, is unknown.