1. ¹Department of Biology, Technion-Israel Institute of Technology, Haifa, Israel
2. ²Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
3. ³Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel

Correspondence: Professor MF Polz, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. E-mail: mpolz@mit.edu; Professor O Béjà, Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel. E-mail: beja@tx.technion.ac.il

⁴These authors contributed equally to this work.

Received 15 January 2007; Revised 19 February 2007; Accepted 19 February 2007.

Abstract

Proteorhodopsins (PRs) phototrophy was recently discovered in oceanic surface waters. PRs have been observed in different marine environments and in diverse taxa, including the ubiquitous marine alphaproteobacterial SAR11 group and the uncultured gammaproteobacterial SAR86 group. Previously, two SAR86 PR subgroups, discovered in the Pacific Ocean, were shown to absorb light with different maxima, _max 527 nm (green) and _max 490 nm (blue) and their distribution was explained by prevailing light conditions – green pigments at the surface and blue in deeper waters. Here, we show that PRs display high diversity in geographically distinct patterns despite similar physical water column properties such as mixing and light penetration. We compared summer and winter samples representing stratified and mixed conditions from both the Mediterranean and Sargasso Sea. As expected, in the Mediterranean Sea, green pigments were mainly confined to the surface and the percentage of blue pigments increased toward deeper samples; in the Sargasso Sea, unexpectedly, all PRs were of the blue type. As an additional result, both locations show seasonal dependence in the distribution of different PR families. Finally, spectral tuning was not restricted to a single PR family as previously reported but occurs across the sampled PR families from various microbial taxa. The distribution of tunable PRs across the PR tree suggests that ready adaptability has been distributed widely among microorganisms, and may be a reason that PRs are abundant and taxonomically widely dispersed.