Sulphur metabolism in unicellular marine algae – from biochemical pathway to climate cooling

Joint project with Dr. Gill Malin, ENV, UEA

Primary producers play a critical role in food webs and the global biogeochemical sulfur cycle because they are able to assimilate inorganic sulfate. Whereas sulfur-deficiency is a major issue for agriculture, the oceans are a major global sulfur reservoir and it is thought that sulfur does not limit growth in marine primary producers. The role of marine algae in production of the climate-cooling gas dimethyl sulfide (DMS) has been a major focus, but little is known about the link between sulfate assimilation and the production of the algal DMS precursor dimethylsulfoniopropropionate (DMSP).

Recent progress in algal genomics, especially the genome sequencing of the diatoms Thalassiosira pseudonana and Phaeodactylum tricornutum and the haptophyte Emiliania huxleyi, and the availability of EST libraries from other marine microalgae, allows the use of molecular methods for analysis of ecophysiological processes in the phytoplankton for the first time. The aim of this project is to address the genetic diversity of sulfate assimilation in marine microalgae using bioinformatics, biochemical and molecular methods. A combination of metabolite and expression analysis of the model species T. pseudonana and E. huxleyi will be used to characterise the link between sulfate assimilation and DMSP production and determine the limiting metabolic steps.

 

In addition, exploitation of biodiversity across the kingdoms has been very valuable to obtain plants with improved properties, e.g. using diatom enzymes to alter the composition of fatty acids in seed-rape oil, or using algal flavodoxin to improve stress resistance. Also our previous work on S metabolism in the moss Physcomitrella patens showed the potential for exploration of newly sequenced genomes to identify new enzymes or new variants of existing enzymes. These genes result from adaptations to specific environmental conditions and thus represent excellent resources for studies of structure/function relationship and mechanisms of enzymes, evolution of metabolic pathways, and possibly for improvement of nutrient use efficiency of higher plants. We are comparing the responses of marine microalgae to sulfate and nitrate deficiency with the responses of plants and green algae to identify common and specific genes and processes.