Cyanobacterial Diversity and Specificity in Plant Symbioses

Abstract

Cyanobacteria are a large group of microorganisms, of which only a few genera have symbiotic capacity. To be symbiotically competent, an extreme adaptability of the cyanobacteria is required. They must be capable of adapting to the conditions offered by the host and alter their metabolism to be in a mutualistic state, exchanging metabolites with the host. Another prerequisite of symbiotic cyanobacteria, which form symbioses with plants, is their capacity to differentiate motile filaments, hormogonia, which constitute the “infection unit”. Although numerous cyanobacteria produce motile hormogonia, the capacity to enter into symbioses with plants is restricted to a few genera (Table 1). In addition, the cyanobacteria must exist as free-living in the close vicinity of the potential host. Nostoc is the most dominating genus in terrestrial symbiotic systems, forming symbioses with fungi, bryophytes, Azolla, cycads, and Gunnera. 313