Convergent evolution and horizontal gene transfer in Arctic Ocean microalgae

Abstract

Microbial communities in the world ocean are affected strongly by oceanic circulation, creating characteristic marine biomes. The high connectivity of most of the ocean makes it difficult to disentangle selective retention of colonizing genotypes (with traits suited to biome specific conditions) from evolutionary selection, which would act on founder genotypes over time. The Arctic Ocean is exceptional with limited exchange with other oceans and ice covered since the last ice age. To test whether Arctic microalgal lineages evolved apart from algae in the global ocean, we sequenced four lineages of microalgae isolated from Arctic waters and sea ice. Here we show convergent evolution and highlight geographically limited HGT as an ecological adaptive force in the form of PFAM complements and horizontal acquisition of key adaptive genes. Notably, ice-binding proteins were acquired and horizontally transferred among Arctic strains. A comparison withTaraOceans metagenomes and metatranscriptomes confirmed mostly Arctic distributions of these IBPs. The phylogeny of Arctic-specific genes indicated that these events were independent of bacterial-sourced HGTs in Antarctic Southern Ocean microalgae.

Diatom adhesive trail proteins acquired by horizontal gene transfer from bacteria serve as primers for marine biofilm formation

“…This assumption is supported by the following observation. Diatoms living in polar habitats, like Fragilariopsis cylindrus , produce ice binding proteins (IBPs) that protect them from freezing and also serve to attach cells to ice (Raymond & Kim, 2012; Mock et al ., 2017; Dorrell et al ., 2023). Based on sequence analysis F. cylindrus contains three proteins with a type-1 CAA-domain (Fig.…”

“…As the CAA-domain is present in numerous, but not all raphid diatoms, it not essential for gliding motility. Recent studies suggest that HGT is continuously occurring in diatoms and that there is a high rate of HGT loss due constant environmental pressures and ecological niche adaption (Dorrell et al ., 2021; Dorrell et al ., 2023). Of particular note is the recent description of Antarctic vs Arctic clades of diatom IBPs that suggests two independent HGT events for these two Polar Regions (Dorrell et al ., 2023).…”

“…Recent studies suggest that HGT is continuously occurring in diatoms and that there is a high rate of HGT loss due constant environmental pressures and ecological niche adaption (Dorrell et al ., 2021; Dorrell et al ., 2023). Of particular note is the recent description of Antarctic vs Arctic clades of diatom IBPs that suggests two independent HGT events for these two Polar Regions (Dorrell et al ., 2023). This genome plasticity may therefore help to explain our inability to identify a single ‘universal’ adhesive protein employed by motile diatoms as HGT acquisitions and losses occurring in their local habitat may have allowed for the evolution of a diverse set of species-specific adhesive proteins.…”

Diatom adhesive trail proteins acquired by horizontal gene transfer from bacteria serve as primers for marine biofilm formation

“…Recent studies suggest that HGT is continuously occurring in diatoms and that environmental pressures and ecological niche adaption result in a high rate of HGT loss (Dorrell et al, 2021(Dorrell et al, , 2023. Of particular note is the recent description of Antarctic vs Arctic clades of diatom IBPs that suggests two independent HGT events for these two Polar Regions (Dorrell et al, 2023).…”

“…Recent studies suggest that HGT is continuously occurring in diatoms and that environmental pressures and ecological niche adaption result in a high rate of HGT loss (Dorrell et al, 2021(Dorrell et al, , 2023. Of particular note is the recent description of Antarctic vs Arctic clades of diatom IBPs that suggests two independent HGT events for these two Polar Regions (Dorrell et al, 2023). This genome plasticity may account for our inability to identify a single 'universal' adhesive protein, as species-specific adhesive proteins can evolve through HGT acquisitions and losses in their local habitat.…”