Evolution of marine roseobacters at different timescales
Ph.D. Roseobacters are known ecological generalists equipped with tremendous metabolic capabilities and various ecological roles. However, the timing and evolutionary underpinnings of Roseobacter ecological diversification are still under active discussion. In this thesis, molecular evolutionary app...
| Other Authors: | , , |
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| Format: | Text |
| Language: | English Chinese |
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2018
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| Online Access: | https://julac.hosted.exlibrisgroup.com/primo-explore/search?query=addsrcrid,exact,991039750411903407,AND&tab=default_tab&search_scope=All&vid=CUHK&mode=advanced&lang=en_US https://repository.lib.cuhk.edu.hk/en/item/cuhk-2188666 |
| Summary: | Ph.D. Roseobacters are known ecological generalists equipped with tremendous metabolic capabilities and various ecological roles. However, the timing and evolutionary underpinnings of Roseobacter ecological diversification are still under active discussion. In this thesis, molecular evolutionary approaches were addressed to gain insights into these questions from different timescales of resolution. First, we developed a fossil-independent approach to understand the evolutionary timescale of marine roseobacters. This approach is based on the spontaneous mutation rate determined for a model Roseobacter strain using a mutation accumulation experiment, among the first for a marine bacterium, and growth rates typical for the taxon in the ocean. This analysis first gives estimates of evolutionary time for closely related taxa, and subsequently extrapolates the timing estimates for more divergent lineages by leveraging the molecular clock approach. Using the calculated mutation rate of 1.39×10-10 per base per generation, we implement a “mutation-rate clock” approach to date the evolution of roseobacters by assuming a constant mutation rate along their evolutionary history. This approach gives an estimated date of Roseobacter genome expansion in good agreement with an earlier fossil-based estimate of approximately 250 million years ago and is consistent with a hypothesis of a correlated evolutionary history between roseobacters and marine eukaryotic phytoplankton groups. In the second part, we reported a nearly complete genome co-assembly of the Roseobacter DC5-80-3 Antarctic phylotype, and compare it to the available genomes of the other phylotype from ocean regions where iron is more accessible but phosphorus and nitrogen are less. The Antarctic phylotype exclusively contains an operon structure consisting of a dicitrate transporter fecBCDE and an upstream regulator binding site likely for iron uptake, whereas the other phylotype consistently carry a high-affinity phosphate pst transporter and the phoB-phoR ... |
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