Nostoc azollae 0708

The order Nostocales grow as unbranched filaments and produce up to three kinds of differentiated cells. Heterocysts differentiate in response to the lack of nitrogen in the environment and are the sites of nitrogen fixation (3-10% of total cells). Nostoc species also produce relatively short, motile filaments called hormogonia and spore-like structures termed akinetes in response to nutrient limitation other than nitrogen. Nostoc species are widely distributed in illuminated portions of the biosphere, including fresh waters and tropical, temperate and polar terrestrial systems; they are rarely found in marine habitats. Growth is often as a colony of filaments within a gelatinous matrix. Many Nostoc species occur in symbiotic associations with fungi to form lichens and with representatives of each of the major phylogenetic groups of plants. They are major contributors to the sequestration of CO2 in organic compounds, especially in nutrient poor and extreme environments.Nostoc azollae strain 0708 is a symbiont of the free-floating water fern Azolla filiculoides, and is both photosynthetic and able to fix nitrogen. Nostoc colonizes cavities in the dorsal leaves of Azolla; the plant supplies the cyanobiont with fixed carbon, and receives a perpetual source of combined new nitrogen from the nitrogen-fixing cyanobiont. The cyanobiont is vertically transmitted into new plant generations within the plant reproductive organs, the sporocarps. The Nostoc cyanobiont seems to have lost its capacity for independent growth. The cyanobiont produces combined nitrogen, and as a side-reaction, the nitrogen-fixing enzyme also produces hydrogen gas, a potentially important bio-gas. This symbiotic system has been known in south-east Asia for over 1000 years, where is has been used to sustain agricultural productivity (adapted from http://genome.jgi-psf.org/anaaz/anaaz.home.html). (HAMAP: NOSA0)