A new energy-generating, light-absorbing pigment called proteorhodopsin is widespread in the world's oceans, say scientists funded by the National Science Foundation (NSF) and affiliated with the Monterey Bay Aquarium Research Institute (MBARI). Their discovery is reported in this week's issue of the journal Nature. Last fall in the journal Science, the MBARI researchers described the first marine bacterium with this photopigment that can generate cellular energy using light.
"Advances in technology are letting us view the marine microbial world in new ways," said Ed DeLong, leader of the MBARI research group. Colleague Oded added, "We were lucky to find these different proteorhodopsins out there in the vast ocean."
In the recent study, samples of oceanic bacteria collected from Monterey Bay, Antarctica, and Hawaii were analyzed for the presence of active photopigment. In collaboration with John and Elena Spudich from the University of Texas Medical School, the scientists used laser flash spectroscopic techniques on naturally occurring marine microbes to search for the new photochemical activity in oceanic waters. The scientists observed chemical activity stimulated by light flashes in native marine microbes, similar to the activity seen in earlier laboratory studies of proteorhodopsin and bacteriorhodopsin. These observations showed that the microbes and active photopigment were present in abundance at the ocean's surface.
The researchers also showed that genetic variants of the photoactive microbes contain different proteorhodopsins in different ocean habitats. The protein pigments appear to be tuned to absorb light of different wavelengths that match the quality of light available in different environments. Specific adaptations in the photopigment structure have optimized different variants functioning best at different depths in the water column.
DeLong and his colleagues are excited by the implications of this research. The study takes the initial laboratory observations to the sea, showing how widespread this photopigment is throughout the world's oceans. In addition, the concentration of the photopigment suggests that it has the capacity to generate a significant amount of energy for oceanic microbes.