CorA gene rearrangement triggered the salinity-driven speciation of Poseidoniales

Abstract

ABSTRACTThe rise of microbial species is associated with multiple genetic changes and niche reconstruction 1,2. While recombination, lateral gene transfer and point mutations can contribute to microbial speciation 3, acquisition of niche-specific genes was found to play an important role in initiating ecological specialization followed by genome-wide mutations 4. The critical step at the very early microbial speciation between ecologically distinct habitats, such as land and ocean, however, is elusive. Here we show that the divergence of archaea Poseidoniales between brackish and marine waters was triggered by rearranging a magnesium transport gene corA in a global geological background. The corA gene was inserted within a highly conservative gene cluster and possibly function in concert with the other genes in this cluster in osmotic stress response. It then went through sporadic losses and gains that were coincident with the Pangea tectonic activities and sea-level rising. Notably, metabolic adjustment and proteome-wide amino acid substitution were found after the change of corA. Our results highlight salinity adaptation as the primary factor in microbial speciation at the interface between land and ocean. Such a process can start from simply changing one gene but may need coherent gene cluster rearrangement and work in tune with strong selective forces such as global landform changes.