The “Cheshire Cat” mechanism of Emiliania huxleyi and its wider implications
The coccolithophore E.huxleyi is a heavily studied organism, due to both its position as one of the most abundant eukaryotes in the ocean and the way in which it forms vast blooms in both northern and southern hemisphere (Frada et al., 2008)Furthermore, these blooms have been identified to have a considerable impact on the planet; they influence global temperatures through the sunlight that they reflect and uptake atmospheric carbon dioxide (Rohwer and Thurber, 2009). Beyond this, marine studies are fascinated by the way in which the algae’s lifecycle is intertwined with that of the E. huxleyi virus (EhV), with studies showing that the virus is responsible for thesudden termination of the blooms (Wilson et al., 2002) which often occur. When looking into these blooms and their swift decimation by EhV, it was found that it does not necessarily follow the expected mechanic of interaction.
If the populations of the coccolithophore were being routinely destroyed by this virus, it would be reasonably expected that the algae would be subject to selective pressure. In turn, the EhVs would be equally pressured to find a way around the new resistance and the cat and mouse game would continue. This ‘Red Queen’ hypothesis can indeed be seen to some extent within E. huxleyi. However, studies of multiple generations of their blooms have shown that the same genotypes of both the algae and its virus are dominant over a period of generations (Martinez et al., 2006). The mechanism that was identified by Miguel Frada and his team (2008) as being responsible was a novel one; coined the ‘Cheshire Cat’ effect, the coccolithophore changed from one lifecycle phase to another in order to completely evade the EhV. Specifically, E. huxleyi went from its diploid to haploid stages, with the latter possessing a flagellum and organic scales but no coccoliths (Morin, 2008). In its haploid state, it can wait and recover. The fact that the organism changes in response to its virus makes it all the more intriguing. Whilst the exact mechanism by which this occurs is as of yet unidentified, follow up research by Rokitta et al (2011)has found that “different properties of gene expression” are present in the diploid and haploid stages. In addition, it is concluded that each both stages are “evolutionarily shaped” to each of their niches.
In short, then, it would seem that this strategy allows the haploid phase to escape undetected, a system which is of great interest to not just the specific field of marine virology, but also of a much wider field. The question of whether or not this system is unique to Emiliania huxleyi is a prominent one
Frada, M. et al (2008) The “Cheshire Cat” escape strategy of the coccolithophore Emiliania Huxleyi in response to viral infection
Rohwer, F; Thurber, V.T. (2009) Viruses manipulate the marine environment, Nature vol. 459
Wilson, W.H. et al, (2002) Isolation of viruses responsible for the demise of an Emiliania huxleyi bloom in the English Channel
Martinez, J;Schroeder, D.C; Larsen, A; Bratbak, Gunnar; Wilson, W.H (2006), Applied and Environmental Microbiology, 73:554-562
Morin, Peter J. (2008), Sex as an algal antiviral strategy, PNAS, 105:15639-15640
Rokitta, S.D; de Nooijer, L.J; Trimborn, S; de Vargas, C; John, U; Rost, B. (2011), Transcriptome analyses reveal differential gene expression patterns between the life-cycle stages of Emiliania huxleyi (haptophyta) and reflect specialization to different ecological niches, Phycological Society of America, 47:829-838