Relationship between nitrogen fixation and numbers of cyanobionts and heterocysts in fifteen Azolla strains

The relationship between nitrogen fixation and the numbers of cyanobionts and heterocysts in the mature leaves of fifteen Azolla strains from five species was examined. The nitrogenase (acetylene reduction) activity per leaf and the numbers of cyanobionts and heterocysts in the mature region varied depending on the Azolla strains. The numbers of cyanobionts and heterocysts, particularly the number of heterocysts, were closely correlated with the nitrogenase activity per leaf. However, the nitrogenase activity per leaf was not correlated with the nitrogenase activity per heterocyst. The results indicate that the variation in the nitrogenase activity of the leaves among Azolla strains mainly resulted from the variation in the number of heterocysts and not from the variation in the nitrogenase activity per heterocyst.     

Symbioses of Cyanobacteria in Marine Environments: Ecological Insights and Biotechnological Perspectives

Cyanobacteria are a diversified phylum of nitrogen-fixing, photo-oxygenic bacteria able to colonize a wide array of environments. In addition to their fundamental role as diazotrophs, they produce a plethora of bioactive molecules, often as secondary metabolites, exhibiting various biological and ecological functions to be further investigated. Among all the identified species, cyanobacteria are capable to embrace symbiotic relationships in marine environments with organisms such as protozoans, macroalgae, seagrasses, and sponges, up to ascidians and other invertebrates. These symbioses have been demonstrated to dramatically change the cyanobacteria physiology, inducing the production of usually unexpressed bioactive molecules. Indeed, metabolic changes in cyanobacteria engaged in a symbiotic relationship are triggered by an exchange of infochemicals and activate silenced pathways. Drug discovery studies demonstrated that those molecules have interesting biotechnological perspectives. In this review, we explore the cyanobacterial symbioses in marine environments, considering them not only as diazotrophs but taking into consideration exchanges of infochemicals as well and emphasizing both the chemical ecology of relationship and the candidate biotechnological value for pharmaceutical and nutraceutical applications.