Review

Desiccation tolerance in cyanobacteria

Nidheesh Dadheech

Department of Biochemistry, Faculty of Science, the Maharaja Sayajirao University of Baroda, Vadodara, Gujarat, India. E-mail: dadheech_21@yahoo.co.in.

Accepted 6 July, 2010

   Abstract

All abiotic stresses adversely affect growth and development of cells. Direct effect of these factors results into condensation of nucleoid, crowding of cytoplasmic components, and increase in the T_m of membrane phase transition. Cells under prolonged exposure to these stresses, show pronounced effect on proteins, nucleic acids, and lipid membranes. Those that have developed mechanisms for acclimation only survive under unfavorable conditions. Bound water in both proteins and nucleic acids plays extensive role in tolerance to stress. Water stress proteins are most abundant proteins, in cynobacteria, accumulated in extracellular glycan sheath and releases during desiccation. Besides these, Histones-like DNA binding proteins maintain nucleoid organization and regulate DNA repair. Certain special enzymes “Repair Ligases” also provide tolerance to bacterial cells, under stress conditions especially desiccation. Number of chromosome copies per cell is also important to this act the lethal effect of stress. Membrane fluidity plays important role in temperature perception, which is mediated by Histidine Kinases, localized in plasma membrane. Fatty acid desaturases (enzyme) enhance degree of unsaturation of fatty acids in the plasma membrane that is inducing double bonds in fatty acids, as a consequence of which Des A gene is expressed (in low temperature stress). Cyanobacteria accumulate compatible solutes in response to increases external salinity. Tolerance increases from sucrose or trehalose to glucosylglycerol and glycinebetamine accumulating species. Na⁺/H⁺ antiporters are responsible for salt and pH regulation in Synechocystis. The present review combines and compares all the abiotic stress mechanisms including desiccation, temperature, pH and salinity. It also underlines the common mechanistic pathways in all the stress operating in cynobacteria as well as highlights the signaling molecules that play pivot role in tolerance for stress and that are common in different mechanisms.

Key words: Cyanobacteria, desiccation, tolerance, mechanism, proteins, nucleic acids, membranes.