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Coccolithoviruses (EhVs) are large, double-stranded DNA-containing viruses that infect the single-celled, marine coccolithophore Emiliania huxleyi. Given the cosmopolitan nature and global importance of E. huxleyi as a bloom-forming, calcifying, photoautotroph, E. huxleyi-EhV interactions play a key role in oceanic carbon biogeochemistry. Virally-encoded glycosphingolipids (vGSLs) are virulence factors that are produced by the activity of virus-encoded serine palmitoyltransferase (SPT). Here, we characterize the dynamics, diversity and catalytic production of vGSLs in an array of EhV strains in relation to their SPT sequence composition and explore the hypothesis that they are a determinant of infectivity and host demise. vGSL production and diversity was positively correlated with increased virulence, virus replication rate and lytic infection dynamics in laboratory experiments, but they do not explain the success of less-virulent EhVs in natural EhV communities. The majority of EhV-derived SPT amplicon sequences associated with infected cells in the North Atlantic derived from slower infecting, less virulent EhVs. Our lab-, field- and mathematical model-based data and simulations support ecological scenarios whereby slow-infecting, less-virulent EhVs successfully compete in North Atlantic populations of E. huxleyi, through either the preferential removal of fast-infecting, virulent EhVs during active infection or by having access to a broader host range., (© 2019 Society for Applied Microbiology and John Wiley & Sons Ltd.)

Understanding the genetic underpinnings of adaptive traits in microalgae is important for the study of evolution and for applied uses. We used long-term selection under a regime of serial transfers with haploid populations of the green alga Chlamydomonas reinhardtii raised in liquid TAP medium containing 200 mM NaCl. After 1255 generations, evolved salt (ES) populations could grow as rapidly in high salt medium as progenitor cells (progenitor light [PL]). Transcriptome data were analysed to elucidate the basis of salt tolerance in ES cells when compared with PL cells and to cells incubated for 48 h in high salt medium (progenitor salt [PS], the short-term acclimation response). These data demonstrate that evolved and short-term acclimation responses to salt stress differ fundamentally from each other. Progenitor salt cells exhibit well-known responses to salt stress such as reduction in photosynthesis, upregulation of glycerophospholipid signaling, and upregulation of the transcription and translation machinery. In contrast, ES cells show downregulation of genes involved in the stress response and in transcription/translation. Our results suggest that gene-rich mixotrophic lineages such as C. reinhardtii may be able to adapt rapidly to abiotic stress engendered either by a rapidly changing climate or physical vicariance events that isolate populations in stressful environments., (© 2013 Society for Applied Microbiology and John Wiley & Sons Ltd.)