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

Abstract

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.

Keywords: animal interactions; bioactive molecules; cyanobionts; diazotroph; infochemicals; prokaryotes; secondary metabolites.

Figure 1

Symbioses of cyanobacteria. In this figure are summarized the symbioses among different cyanobacteria taxa with different hosts.

Figure 2

Structure of bioactive compound produced by symbiotic cyanobacteria.

Figure 3

Ecological relevance of cyanobacteria in symbioses. Cyanobacteria symbioses have an important role in nutrient supply and energy supply, such as diazotrophy or photosynthesis. Cyanobacteria can also produce bioactive molecules that protect the host (i.e., anti-grazing compounds). In addition, the host can induce metabolic variation in cyanobacteria; indeed, several organisms are able to produce chemoattractants and hormogonia-inducing factors that allow symbiosis establishment and persistence.

Figure 4

Schematic representation of hormogonia induction and repression in cyanobacterial symbiosis. Hormogonia motile forms, stimulated by several inducing factors that act as chemoattractants, are able to infect the host. Once infected, the host produces hormogonia-reducing factors, reconstituting the symbiosis.