Functional Comparative Analysis of Proteorhodopsin and NQ Rhodopsin Genes from Isolates of Marine Flavobacteria

Abstract

Diverse rhodopsin-containing microorganisms function as energy-transducing light-driven proton or chloride pumps, or as phototactic sensory proteins. Since the proteorhodopsin (PR) functioning as a light-driven proton pump was first discovered from SAR86 group, a new type of rhodopsin (NaR), that function as a light-driven sodium ion pump, was recently reported from Krokinobacter eikastus and Nonlabens dokdonensis. In the present study we investigated novel NaR from previously reported PR-containing Flavobacteria which were isolated from marine samples such as water, sediment, organisms, etc. Out of 16 PR-containing isolates, 4 contained NaR gene. On the basis of three full sequences and one partial, it was confirmed that the key active site residues in typical feature of the rhodopsin (D85 and D96 in Bacteriorhodopsin) are replaced by N112 and Q123. Phylogenetic analysis indicated four NaR formed a same clade with two previously reported NaR. The light-driven inward or outward proton pump activity of native cell suspensions from marine Flavobacteia isolates containing both PR and NaR genes was discriminated depending upon the culture time. This study shows the involvement of NaR light-driven energy synthesis might more actively function in the early growth phase (logarithmic) of cells before PR gene function becomes active in the late growth phase (stationary) of cells and the NaR containing Flavobacteria mighred from SAR86 group, a new type of rhodopsin (NaR), that function as a light-driven sodium ion pump, was recently reported from Krokinobacter eikastus and Nonlabens dokdonensis. In the present study we investigated novel NaR from previously reported PR-containing Flavobacteria which were isolated from marine samples such as water, sediment, organisms, etc. Out of 16 PR-containing isolates, 4 contained NaR gene. On the basis of three full sequences and one partial, it was confirmed that the key active site residues in typical feature of the rhodopsin (D85 and D96 in Bacteriorhodopsin) are replaced by N112 and Q123. Phylogenetic analysis indicated four NaR formed a same clade with two previously reported NaR. The light-driven inward or outward proton pump activity of native cell suspensions from marine Flavobacteia isolates containing both PR and NaR genes was discriminated depending upon the culture time. This study shows the involvement of NaR light-driven energy synthesis might more actively function in the early growth phase (logarithmic) of cells before PR gene function becomes active in the late growth phase (stationary) of cells and the NaR containing Flavobacteria migh