Nostoc commune is a nitrogen-fixing photosynthetic cyanobacterium with the capacity for desiccation-tolerance. This microorganism grows freely as single filaments (seriate growth) or in aggregates where filamentous organization of the cells is indistinct (aseriate growth). Cells of the aseriate type express a pronounced tolerance to extremes of water stress and accumulate massive amounts of a class of soluble acidic proteins when they are subjected to repeated cycles of drying and rehydration. One of these water stress (Wsp) proteins is a glycoprotein, two others are intimately associated with carbohydrate(s). The aims of this project are to purify and characterize biochemically the Wsp proteins and associated carbohydrates, understand how the synthesis of the proteins is controlled by water stress, and to discover the role of Wsp proteins in desiccation tolerance. Techniques used in this study involve semi-continuous and synchronized growth of cells in a fermenter, immobilization and growth of cells on inert solid supports, protein purification, protein A-gold immunolabelling, and assays for nitrogen fixation including the detection of nifH mRNA in cells subjected to water stress. There is no consensus of opinion on the sequence of events that leads to the suppression of plant growth by waterstress. The objective of this work is to contribute to our understanidng of desiccation tolerance. Consequently, the work is significant in view of the extent to which water deficits impinge upon the success of managed agriculture as well as the fundamental importance of water in gene expression.
