Scientists reassess the impact of ocean bacteria on global warming
Research carried out by scientists in France and the UK has shed new light on the role played by an ocean bound bacterium in controlling atmospheric levels of carbon dioxide, a key greenhouse gas. Prochlorococcus cyanobacteria are the most abundant photosynthetic bacteria in the world's oceans. They use sunlight to convert carbon dioxide into organic molecules, which they then store deep below the surface. The study, carried out by researchers from Imperial College London and the Observatoire Oceanologique Roscoff, reveals for the first time the crucial role played by iron in the photosynthetic process. The team's work was supported by EU funding under the 'quality of life' section of the Fifth Framework Programme. The study's lead author, Professor Jim Barber of Imperial College, said: 'Until recently the contribution of marine photosynthesis to the global carbon cycle was grossly underestimated. We now know that over 50 per cent of global photosynthetic activity takes place in the oceans.' Prochlorococcus lives at widely varying ocean depths, from the surface to 200 metres below sea level. Until now, it was not known how the bacteria were able to maximise the little available sunlight at lower depths in order to fuel photosynthesis. The team discovered that those strains of bacteria that survive in extreme low light conditions are able to recruit additional, or 'antenna', proteins in order to drive the photosynthetic process. Furthermore, their work revealed that iron is the key limiting nutrient that regulates the organism's ability to harvest light energy. The relative scarcity of iron in the Earth's oceans therefore decreases the ability of Prochlorococcus to grow and reproduce, explained Professor Barber: 'Iron is the fourth most abundant element in the Earth's crust. Yet its levels in the aquatic ecosystem, particularly in open oceans where most cyanobacteria are found, is low. 'Indeed, in experiments where regions of the ocean have been artificially seeded with extra iron there is a dramatic increase in biomass production due to an increased amount of Prochlorococcus and other photosynthetic organisms. Our research opens up the possibility of artificially increasing ocean levels of iron to combat global warming,' he concluded.
Countries
France, United Kingdom