Microalga go viral for saltwater adaptation

Microalgae are found in every biome and play a fundamental role in many ecosystems, yet in some ways we know less about them than about other microorganisms. For example, researchers have sequenced only 62 algal genomes, but more than 30,000 bacterial genomes. Examining algal genomes would clarify their evolutionary history and could provide clues to how they have adapted to different environments, including freshwater and saltwater habitats.

To that end, researchers in the UAE, the USA and Saudi Arabia cultivated 107 species of microalgae. They sequenced their genomes and analysed them together with the existing algal genomes to uncover patterns of selection and other evolutionary processes.

The analyses revealed significant differences between freshwater and saltwater species. The genomes of freshwater species had genes with more functional diversity, probably because of reduced selection in freshwater environments. Saltwater genomes were enriched in genes related to cellular and organelle membranes, in keeping with the importance of maintaining membrane integrity in saline environments. 

A striking finding was the integration of more genes from viruses in the genomes of marine species. Kourosh Salehi-Ashtiani of New York University Abu Dhabi, senior author of the study, says that this “point to evolution is a more dynamic process than often recognized, at least with respect to the exchange of genetic material between unrelated species through viruses.” 

Frank Aylward, of Virginia Tech, recently published similar findings about a group of algae known as chlorophytes, though he wasn’t involved in this research. “I agree with these authors that viruses, in particular giant viruses, appear to play an important role in the genome evolution of their hosts. Endogenous viruses likely influence many aspects of their host’s genome evolution and therefore their niche adaptation.”

Aylward also notes that the genomes “will be an excellent resource for scientists working in this field” and that these findings will serve as a useful framework for further research, adding that laboratory experiments will be needed to investigate the phenotypic effects of the viral genes. 

“We often view viruses as harmful elements. We can now see them as having played a facilitator role at the evolutionary timescale,” says Salehi-Ashtiani. 

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