Critically low levels of iron in seawater are inhibiting the growth of microscopic marine microalgae responsible both for the absorption of carbon dioxide (CO2) into the oceans and also for the formation of harmful algal blooms. In a new study, published online this week by Proceedings of the National Academy of Sciences, SAMS researchers and their international collaborators have discovered that a group of bacteria found in close association with the microalgae, provide them with a highly valuable source of iron.
The bacteria produce an iron-binding compound called vibrioferrin, which degrades exceptionally easily in sunlight, releasing a reduced form of iron that is taken up by the microalgae the bacteria live with. Thus, the bacteria provide the algae with readily available iron and in return, the bacteria gain photosynthetic sugars secreted by the algae.
Dr Dave Green of SAMS explains:
“We have discovered a new symbiosis, in which the growth and survival of many bloom-forming microalgae appear to require this close association with specific bacterial species.”
“The findings have provided us with a new understanding of the complexity of life in the oceans, but also raised important questions: could these bacteria shape the evolution of algae, especially in times of rapid environmental change?”
The increasing interest in mass algal culture (e.g. for biofuel or omega-3 fatty acid food supplements) means that the role and importance of bacteria should be considered as beneficial.
Such mutualistic sharing of iron and fixed carbon has important implications for our understanding of the close beneficial interactions between marine bacteria and microalgae, and the effect of these interactions on algal productivity and climate. The finding may also provide clues to some of the mechanisms triggering harmful algal blooms.