The molecular biology of desiccation tolerance was investigated in the cyanobacteria with emphasis on Nostoc commune. Analysis of DNA from 41 samples of desiccated Nostoc spp. of varied age and global distribution led to the amplification of 43 independent tRNALEU(UAA) group 1 intron sequences. Phylogenetic analysis of the entire data set made it possible to define the form species Nostoc commune. The synthase (spsA) and phosphatase (sppA) genes required for the synthesis of sucrose were isolated from cyanobacterium Synechocystis sp. strain PCC 6803 and overexpressed in E. coli in two different vector constructions. Transformants had a marked increased capacity for desiccation tolerance. Sucrose synthesis was confirmed through thin layer chromatography (TLC) analysis of cell extracts from transformants. Long-term stability of DNA in desiccated Nostoc samples was demonstrated by the ability to amplify selected gene loci from samples stored dry for decades. Successful amplification in some samples was possible only after treatment with phenacylthiazolium bromide, a reagent that disrupts covalent cross-links; indicating that the DNA was modified by cross-links that occurred between reducing sugars and the primary amines on the DNA. Abundant superoxide dismutase was released following rehydration of desiccated field material N. commune CHEN after 13 years in the dry state. sodF mRNA was present in the dry material but was turned over within 15 min of rehydration. mRNA levels then rose and appeared to reach steady state levels after 3 hours and remained abundant after 24 hours of rehydration.

Master of Science