Cyanobacteria – invisible, but green
Have you ever seen green-colored water in a lake or a river, just by its side? The water is colored by the presence of tiny single-cellular photosynthetic organisms called Cyanobacteria. While being nethier plants, nor bacteria, those microorganisms resemble the features that could be found in both of those kingdoms, such as lack of nucleus or photosynthetic ability to use light and carbon dioxide to produce sugars, and thus are often considered by scientists as an intermediate separate taxon. Fundamental research in Cyanobacteria benefit our knowledge on both bacterial and plant biology.
One cell – many problems
Life in water, whether fresh or salty, is not easy for a single cell. The only barrier it has from the environment is its own plasma membrane – a tiny layer to protect the presious matter of the cell. Special proteins, called receptors, are located in the membrane here and there, and are the first to experience changes that happen to the membrane due to events happening outside.
Heat will cause stretching of the membrane, and in reverse – cold temperatures, as well as high concentration of salts for a fresh-water living cyanobacteria, will cause the stiffness and squeezing of the membrane, which will affect the cell’s survival. In order to restore the membrane quality and functionality, the cell must turn on protective mechanisms: membrane receptors sense the changes, send the signal of stress to their protein partners – response regulators, – which will assist with turning on a set of specific genes in the cell’s DNA to mediate the defence and later recovery of the cell.
Stress response in Cyanobacteria
While the mechanism of sensing and relaying of the stress signal to the DNA is pretty much general in all living organisms, the amount of the receptors and relaying proteins in the pathway from the membrane to reach the genes could be different for various living forms. Through a through study of the genes of cyanobacteria, we discovered that the environmental stress in them is elaborated by only a pair of proteins: a sensor histidine kinase (Hik) and a relaying response regulator (Rre). Rre contacts directly with the DNA, thus we call it a “two-component system”. There are 45 pairs of Hik/Rre in cyanobacterium Synechocystis, each pair is responsible for the response to a specific stress. As a part of my Doctoral Thesis research, I identified those pairs, and could confirm for several Hik/Rre pairs which stress they respond to, but indeed that was just a first step into our understanding of the fundamental mechanisms of cellular stress perception and response.
- Shumskaya M.A., Paithoonrangsarid K., Kanesaki Y., Los D.A., Zinchenko V.V., Tanticharoen M., Suzuki I., Murata N. (2005) Identical Hik-Rre systems are involved in perception and transduction of salt signals and hyperosmotic signals but regulate the expression of individual genes to different extents in Synechocystis. J Biol Chem, 280(22):21531-8. Download Full Text (JBC 2005)
- Pathoonrangsarid K., Shumskaya M.A. (co-first author), Kanesaki Y., Satoh S., Tabata S., Los D.A., Zinchenko V.V., Hayashi H., Tanticharoen M., Suzuki I., Murata N. (2004) Five histidine kinases perceive osmotic stress and regulate distinct sets of genes in Synechocystis. J Biol Chem, 279(51):53078-86. Download Full Text (JBC 2004)