Presence of a Haloarchaeal Halorhodopsin-Like Cl– Pump in Marine Bacteria
Our new paper was published in Microbes and Environments. In this paper, we determined the draft genomes of 3 marine Cytophagia (Rubricoccus marinus SG-29T, Rubrivirga marina SAORIC-28T and Rubrivirga profundi SAORIC-476T) and 5 putative microbial rhodopsin genes were found in the genome sequences. One of these genes was heterologously expressed in Escherichia coli cells and the rhodopsin protein named Rubricoccus marinus halorhodopsin (RmHR) was identified as a light-driven inward Cl– pump. Spectroscopic characteristics and the amino acid sequence similarities suggested that this rhodopsin is similar to haloarchaeal halorhodopsin (HR) and cyanobacterial HRs (e.g., SyHR and MrHR), but not ClR found in marine Flavobacteriia. Additionally, a phylogenetic analysis revealed that retinal biosynthesis pathway genes (blh and crtY) belong to a phylogenetic lineage of haloarchaea, indicating that these marine Cytophagia acquired rhodopsin-related genes from haloarchaea by lateral gene transfer. Based on these results, we concluded that inward Cl–-pumping rhodopsin is present in genera of the class Cytophagia and may have the same evolutionary origins as haloarchaeal HR.
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