Diversity for Proteorhodopsin Gene of Flavobacteria Isolated from Marine Environment

Abstract

Rhodopsins are found in the domain of Archaea, Bacteria and Eukarya. The proteorhodopsin (PR) gene was first discovered from the metagenome of an uncultivated SAR86 clade (Gammaproteobacteria). Subsequently, PR genes were found in the bacteria belonging to divergent clades of the Alphaproteobacteria and Flavobacteria from different ocean. The finding of Archaeal-like rhodopsins from diverse organisms such as marine bacteria and Eukarya suggests a potential role for lateral gene transfer in their dissemination. In the present study we suggest a possible mechanism of the lateral gene transfer of PR gene among marine microorganisms. The study was carried out to screen the PR gene from the Flavobacteria isolated from the various marine samples such as water, sediment, organisms, etc in marine environments. Out of 322 isolates, 15 contained PR gene. PR, crt I and blh genes, which are responsible of phototrophic function, were sequenced and comparatively analyzed among 15 isolates. The partial length of PR gene between 100 and 156aa showed the similarity ranged from 70.1 to 93.1% within the Flavobacteria group. The full length PR gene sequence of 242 amino acid from one isolated strain of Sediminicola luteus represented the highest similarity to that of the strain Polaribacter sp. MED152 by 86%. Seven transmembrane domains, typical feature of the rhodopsin protein and several key amino acid residues necessary for energyria belonging to divergent clades of the Alphaproteobacteria and Flavobacteria from different ocean. The finding of Archaeal-like rhodopsins from diverse organisms such as marine bacteria and Eukarya suggests a potential role for lateral gene transfer in their dissemination. In the present study we suggest a possible mechanism of the lateral gene transfer of PR gene among marine microorganisms. The study was carried out to screen the PR gene from the Flavobacteria isolated from the various marine samples such as water, sediment, organisms, etc in marine environments. Out of 322 isolates, 15 contained PR gene. PR, crt I and blh genes, which are responsible of phototrophic function, were sequenced and comparatively analyzed among 15 isolates. The partial length of PR gene between 100 and 156aa showed the similarity ranged from 70.1 to 93.1% within the Flavobacteria group. The full length PR gene sequence of 242 amino acid from one isolated strain of Sediminicola luteus represented the highest similarity to that of the strain Polaribacter sp. MED152 by 86%. Seven transmembrane domains, typical feature of the rhodopsin protein and several key amino acid residues necessary for energy