DIVERSITY OF DNA METHYLATION PATTERN AND TOTAL DNA RESTRICTION PATTERN IN SYMBIOTIC NOSTOC

Attempts were made to use total DNA restriction patterns and the respo nse of purified DNA to treatment with restriction endonucleases to cha racterize several symbiotic Nostoc strains which had been isolated fro m different host plants cultivated in Italy. Among 27 restriction endo nucleases tested, several did not cut any DNA and no significant varia tion in the susceptibility of the genomes to DNA restriction was seen among the strains, Therefore the Nostoc strains could not be separated into groups based on their different susceptibilities to the action o f restriction endonucleases. However, in studies of total DNA restrict ion patterns, the restriction endonucleases BfrI and HpaI gave unique band patterns for each cyanobacterial isolate, Different profiles were even found in strains isolated from host plants belonging to the same species. The results do not support any definition of symbiotic Nosto c genomic groups or species and show that a tight specificity between the host plant and the cyanobacterium might not exist in the symbiotic associations involving Nostoc.