Cyanobacteria In Symbiosis PDF Download

The cyanobacteria are a unique and important phylum of bacteria. They are photosynthetic, thought to be responsible for up to half of all atmospheric carbon dioxide fixation, and are capable of fixation of atmospheric nitrogen, thus contributing to the nitrogen cycle. Many species readily form symbiotic relationships with a variety of other organisms, from marine animals, through mosses and lichens, to large land plants. The precursor to the modern chloroplast is thought to have been a cyanobacterium. They have played, and continue to play, a huge part in the formation of the environment of the Earth. Using a wide array of monoclonal antibodies to a variety of plant cell wall components, along with a specific reagent (~-glucosyl Yariv reagent), this study has shown that free- living cyanobacteria have components expressed on the outer surfaces of cells with characteristics very much like those of arabinogalactan-proteins (AGPs). AGPs are a class of plant cell wall glycoproteins with a large number of proposed actions in plant growth, development and signalling (including symbiotic signalling). Bioinformatic analysis of the model symbiotic cyanobacterial proteome of Nostoc punctiforme 29133 has suggested that it contains several proteins which share critical characteristics with known plant AGPs. Wider bioinformatic analysis hints at the presence of AGP-like proteins in a wide variety of ; other cyanobacterial species. The study concludes that free-living cyanobacteria produce AGPs and proposes a role for these in extracellular signalling. The study also uses an array of plant cell wall-specific monoclonal antibodies to investigate the potential interactions between Nostoc, a symbiotic cyanobacterial genus, and two of their symbionts, the angiosperm Gunnera and the liverwort B/asia. The presence of AGP- specific epitopes, along with pectins and hemicelluloses at the symbiotic surface is demonstrated. Other than AGPs, analysis suggests that symbiotic cyanobacteria lack the genetic capability to produce these components, and hence it is hvpotheslsed that the plant produces these at the symbiotic surface. Potential roles for these are discussed, including roles in symbiotic signalling and helping the cyanobiont evade plant immune responses.