Filamentous nitrogen fixing cyanobacteria are resistant to desiccation, nutrient depletion, adverse temperature and challenging photic environments. This is generally thought to account for their role as pioneering forms of life on denuded strata. It has also lent credence to the possibility that cyanobacteria with prolonged viability may have been able to survive conditions of interplanetary space to implement a panspermian hypothesis for the origin of life on earth. Prolonged retention of viability had been noted in our collection of myxotrophically grown strains of nostocaceans cultured in liquid or solid media containing calcium carbonate. Such media permitted satisfactory recovery and regrowth after storage at low light intensities for two years or more. Moreover, even the oldest calcium carbonate cultures contained motile hormogonia when observed microscopically.. This phenomenon can be used to advantage in sending cultures to other laboratories. Not only are organisms maintained during passage through the postal system but since the cultures formed hormogonia readily, it was possible to produce preservable homogeneous agar lawns that generated hormogonia as needed for demonstration or experiment. A practical technique consists of seeding axenic strains of Nostoc species grown in liquid shake culture under cool-white fluorescent illumination into solid media containing 0.7% sucrose, 0.05% finely divided calcium carbonate and 1.4% purified agar. The preparations are incubated under red fluorescent illumination to produce several crops of hormogonia in successive cycles of development, within the agar. The heavily grown lawns are cut into disks or squares, then transferred to dishes and dried in desiccators with anhydrous calcium sulfate. The dry patches produce swarms of hormogonia in two or three hours, depending upon the rate of rehydration. The patches are facile tools for purifying cultures through the isolation of hormogonia and studying cyanobacterial physiology by the rapid response of motile hormogonia.

Key words: gliding motility, hormogonia, nostocaceae, preservation, resistance to desiccation