Abstract
The breakthrough of environmental ge-nomics of marine microbes has revealed the exis-tence of eubacterial rhodopsin in the sea, named proteorhodopsin (PR), which can take light to pro-duce bio-energy for cell metabolism. Gene and protein sequence analysis and laser flash-induced photolysis experiments have validated the function of PR as light-driven proton-pump. During the pumping process, light energy is transformed into chemical gradient potential across plasma inner-membrane, the potential energy is then used to synthesize ATP. The finding of PR actually brings to light a novel pathway of sunlight utilization existing in heterotro-phic eubacteria in contrast to the well-known chloro-phyll-dependent photosynthesis in the sea. Since the group of PR-bearing bacteria is one of the numeri-cally richest microorganisms on the Earth, accounting for 13% of the total in sea surface water, and with averaged cellular PR molecules of 2.5×104, PR- bearing bacteria are a key component not to be ig-nored in energy metabolism and carbon cycling in the sea. Based on the understanding of current literature and our own investigation on PR in the China seas which indicated a ubiquitous presence and high di-versity of PR in all the marine environments, we propose a conceptual model of energy flow and car-bon cycling driven by both pigment-dependent and -independent biological utilization of light in the ocean.
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