Phylogenomic Analysis Reveals A Two-Stage Process Of The Evolutionary Transition Ofshewanellafrom The Upper Ocean To The Hadal Zone

Shewanellastrains are characterized by versatile metabolic capabilities, resulting in their wide distribution in the ocean at different depths. Considering that particle sedimentation is an important dynamic process in the ocean, we hypothesized that hadalShewanellaspecies evolved from the upper ocean. In this study, we isolated three novelShewanellastrains from deep-sea sediments in the Southwest Indian Ocean. Genome sequencing indicated that strains YLB-06 and YLB-08 represent two novel species in the genusShewanella. Through phylogenomic analysis, we showed that speciation and genomic changes in marineShewanellastrains are related to water depth. We further confirmed the aforementioned hypothesis and revealed a two-stage process of the evolutionary transition ofShewanellafrom the upper ocean to the hadal zone by comparative genomics and gene gain/loss analysis. Finally, the transcriptomic analysis demonstrated that recently obtained genes are strictly repressed and may thus play a minor role in the response to environmental changes.