Nostoc
•Nostoc is an example of a genus within the order Nostocales and family Nostocaceae.
•These organisms are all within group IV (subgroup I)
•Nostoc present characteristics such as long multicellular filaments, reproduction through random trichome breakage and the ability to differentiate into specialized cell types.
•This ability to perform cellular differentiation means Nostoc is remarkably adaptable to environments which would be uninhabitable by other cyanobacterial groups.
•This group are not only widespread across normal aquatic
and terrestrial environments, but can also be found in extreme habitats such as Antarctica and the Arctic, due to their resistance to desiccation, nitrogen deficiency and cold temperatures (even freeze thaw cycles).
•This ability has meant that the genus Nostoc has been known as one of the most widely distributed groups of photosynthetic bacteria on Earth.
•In order to adapt to their environment and gain these key features of differentiation, there may have been horizontal gene transfer events throughout the evolution of the cyanobacterial phylum.
•The main form of differentiation of Nostoc spp. For example in the species N. commune, is the formation of heterocystous cells.
•The ability to fix nitrogen in some species of the genus Nostoc, can result in symbiotic relationships with organisms such as plants, mosses, lichen and fungi
•Nostoc is a genus which includes a number of very resilient species, allowing them to inhabit (amongst other areas) a number of extreme environments around the world. Their ability to resist environmental change through morphological and physiological differentiation, seems to provide them with a distinct ecological advantage, in the sense that they can thrive where other organisms simply would not be able to.
•As evidence of this, fossils of cyanobacteria have been found from at least 3.4 billion years ago. These fossils showed very limited differences between the organisms we see now. This shows an incredibly slow rate of evolution of this phylum, which must be attributed to their sizeable ecological tolerance to environmental change.