[Resistance of mesospheric microorganisms to periodic freezing--thawing].

The object of this work was to study cytological changes caused by periodic freezing-thawing in the conidia of the fungi Aspergillus niger and Penicillium chrysogenum isolated from the mesosphere as well as in the conidia of the same species taken from the collection of microorganisms. The conidia from the mesosphere were found to be highly resistant to the treatment. As was shown by electron microscopy, the outer "backbone" layer of the spore envelope broke down and the membranes of the plasmalemma stratified after ten cycles in A. niger and P. chrysogenum. The percentage of conidia with the damaged ultrastructural organization was higher in mutants of these cultures.