Morphological switch to a resistant subpopulation in response to viral infection in the bloom-forming coccolithophore Emiliania huxleyi
. PLOS Pathogens 2017
, 1-17. Publisher's VersionAbstract
Author summary This study assesses the interplay between the globally distributed microalga Emiliania huxleyi and its specific lytic viruses, EhV, which drive the termination of vast oceanic blooms. E. huxleyi is characterized by a biphasic life cycle that alternates between morphologically dissimilar diploid and haploid cells. Here, we show that during viral infection, the bloom-forming diploid cells that are sensitive to EhV can produce virus-resistant cells. These latter cells are morphologically similar to the haploid phase but have diploid or aneuploid genomes. Therefore, a mechanism that mediates morphological remodeling appears to be activated during viral infection, enabling E. huxleyi to escape EhV. These results provide novel insights into morphological plasticity and viral resistance in marine phytoplankton, while highlighting the complexity of host–virus interactions in the oceanic microbial realm.
Communication via extracellular vesicles enhances viral infection of a cosmopolitan alga
1485 - 1492. Publisher's VersionAbstract
Communication between microorganisms in the marine environment has immense ecological impact by mediating trophic-level interactions and thus determining community structure1. Extracellular vesicles (EVs) are produced by bacteria2,3, archaea4, protists5and metazoans, and can mediate pathogenicity6or act as vectors for intercellular communication. However, little is known about the involvement of EVs in microbial interactions in the marine environment7. Here we investigated the signalling role of EVs produced during interactions between the cosmopolitan alga Emiliania huxleyi and its specific virus (EhV, Phycodnaviridae)8, which leads to the demise of these large-scale oceanic blooms9,10. We found that EVs are highly produced during viral infection or when bystander cells are exposed to infochemicals derived from infected cells. These vesicles have a unique lipid composition that differs from that of viruses and their infected host cells, and their cargo is composed of specific small RNAs that are predicted to target sphingolipid metabolism and cell-cycle pathways. EVs can be internalized by E. huxleyi cells, which consequently leads to a faster viral infection dynamic. EVs can also prolong EhV half-life in the extracellular milieu. We propose that EVs are exploited by viruses to sustain efficient infectivity and propagation across E. huxleyi blooms. As these algal blooms have an immense impact on the cycling of carbon and other nutrients11,12, this mode of cell–cell communication may influence the fate of the blooms and, consequently, the composition and flow of nutrients in marine microbial food webs.
Expansion of the redox-sensitive proteome coincides with the plastid endosymbiosis
17066. Publisher's VersionAbstract
The redox-sensitive proteome (RSP) consists of protein thiols that undergo redox reactions, playing an important role in coordinating cellular processes. Here, we applied a large-scale phylogenomic reconstruction approach in the model diatom Phaeodactylum tricornutum to map the evolutionary origins of the eukaryotic RSP. The majority of P. tricornutum redox-sensitive cysteines (76%) is specific to eukaryotes, yet these are encoded in genes that are mostly of a prokaryotic origin (57%). Furthermore, we find a threefold enrichment in redox-sensitive cysteines in genes that were gained by endosymbiotic gene transfer during the primary plastid acquisition. The secondary endosymbiosis event coincides with frequent introduction of reactive cysteines into existing proteins. While the plastid acquisition imposed an increase in the production of reactive oxygen species, our results suggest that it was accompanied by significant expansion of the RSP, providing redox regulatory networks the ability to cope with fluctuating environmental conditions.