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 the project are published this week in the journal 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 how physical, chemical and biological processes regulate the Earth's systems. The algae form pale chalky cases called coccoliths which during the spring bloom 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.
Dr Mark Van Der Giezen from the University of Exeter said: "Using comprehensive analysis to compare different strains of the algae, we 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 groups 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.
The study of the E. huxleyi genome shows 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.
Genome sequencing was performed by the US Department of Energy Joint Genome Institute.
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