Emiliania Genome

Mark van der Giezen, Bryony Williams, Darren Soanes and Thomas Richards have contributed to the project.

New technology uncovers secrets of White Cliffs of Dover

Mark van der Giezen, Bryony Williams,Darren Soanes and Thomas Richards from the University of Exeter recently contributed to a major international project to sequence the genome of Emiliania huxleyi, the microscopic plankton species whose chalky skeletons form the iconic White Cliffs of Dover. The results of this project are published this week in Nature.

Emiliania huxleyi is one of the most abundant marine phytoplankton species and is a key player in the process of CO2 exchange between the atmosphere and the ocean. In some marine systems 20% of the total carbon is fixed by E. huxleyi. This microscopic alga has influenced the global climate for over 200 million years, so is used as a model system for studying biosphere-geosphere. Forming pale chalky cases called coccoliths, during the spring bloom it can be seen from space in the seas around the UK. E. huxleyi directly links to climate change through the production of dimethylsulfide (DMS), which induces cloud formation and blocks solar radiation.

Thanks to new technology – next generation DNA sequencing – 13 different isolates were sequenced from around the world, and compared to a complete sequence constructed for E. huxleyi strain CCMP1516. The allowed the team to understand the influences of different environmental conditions on E. huxleyi physiology. The international team found that E. huxleyi possess a higher number of genes than previously published marine phytoplankton genomes, and that most genes were present in multiple copies.

Comprehensive analysis comparing the different strains demonstrated that E. huxleyi should no longer be considered a single species. Substantial variation in the genome indicates contrasting metabolic composition and supports the idea that E. huxleyi is a species complex. Comparing patterns, or phylogenetic relationships, in the genomes of the different strains identified three clades which did not relate to geographic origin nor genome size. Further research into the genomes revealed that the E. huxleyi genome includes core regions shared by all samples with some variable elements. Regions with high levels of tandem repeats and low complexity may have allowed rapid evolutionary adaptation over many millions of years, allowing current strains to live in a range of light conditions.

This study of the E. huxleyi genome shows very many unexpected features that may be unique or common in microalgae warranting further investigation. For example, metabolic pathways, known previously only in fungi and animals that allow lipid synthesis were found. Using this new insight into an age-old algae, there is future potential for E. huxleyi to be used to synthesise nutritional supplements, biofuels, feedstock and polymer precursors, which may make E. huxleyi a valuable species for cutting-edge biotechnology.

The paper 'Pan genome of the phytoplankton Emiliania underpins its global distribution' will be published on the Nature website from 12th June at 18:00.

Date: 11 June 2013

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