A CULTURE-DEPENDENT AND –INDEPENDENT VIEW ON PHOTOHETEROTROPHIC BACTERIA IN THE EASTERN MEDITERRANEAN SEA

Photoheterotrophic bacteria are able to generate energy from sunlight, but are unable of CO₂ fixation thus relying on external organic carbon sources. The two main types of photoheterotrophic bacteria described in the marine environment are proteorhodopsin (PR)-containing bacteria and aerobic anoxygenic photoheterotrophic (AAP) bacteria. The former use a retinal-based proton pump and the latter a chlorophyll-based electron chain to create a proton gradient that can be used for ATP production or substrate transport. Recent data collected offshore during a late autumn cruise, in part across an offshore eddy off the ultra-oligotrophic Israeli Mediterranean coast, suggested an unusually high occurrence of PR-bearing bacteria in offshore waters of the Eastern Mediterranean coast, whereas AAP bacteria were present only in low abundance. Using microscopy we analyzed the seasonal abundance of aerobic anoxygenic photoheterotrophs in a coast to offshore transect. Furthermore we report on the isolation and initial physiological characterization of PR-bearing and AAP bacteria from the offshore Eastern Mediterranean Sea, which will enable theanalysis of the potential functional roles of photoheterophy in this ultra-oligotrophic environment.