The light dependent proton pump proteorhodopsin must be an important source of energy for bacteria in the oligotrophic ocean, as judged by its abundance, diversity, and spectral tuning to specific wavelengths. Until now, proteorhodopsin genes have mostly been found in tropical oceans, and only very few strains carrying proteorhodopsin were successfully cultured, e.g. Pelagibacter ubique SAR11, HTCC2207, and MED134. The latter is the only one were light was actually shown to stimulate growth at low carbon concentrations. Here we determined the diversity of proteorhodopsin genes in the total bacterioplankton of the North Sea close to the island of Helgoland, and isolated and characterized two new strains carrying proteorhodopsin. Using specific primers, cloning and sequencing, a large diversity of proteorhodopsin genes was discovered in the DNA of a filtered North Sea water sample. Oligocarbophilic bacteria were isolated by dilution plating a water sample on media without any added carbon sources except for those naturally present. Plates were incubated at in situ temperature (16°C) in a natural day-night cycle for 4 weeks. Appr. 250 isolates obtained in such a way were screened for the presence of the proteorhodopsin gene by PCR, resulting in the discovery ot two such strains, PRO95 and PRO100. 16S rRNA sequence analysis showed that they belong into the Bacteroidetes phylum. The proteorhodopsin sequence was completed by primer walking and the effect of light was studied in oligocarbophilic media.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > CO2-Coastal diversity - key species and food webs