CHARACTERISTICS OF A CESIUM-RESISTANT (C-S(-R) MUTANT OF THE N-2-FIXING CYANOBACTERIUM NOSTOC-MUSCORUM - DEPENDENCE ON CS+ OR RB+ FOR NORMAL DIAZOTROPHY AND OSMOTOLERANCE())

Spontaneous mutation of the cyanobacterium Nostoc muscorum to a caesiu m resistant (Cs+-R) phenotype resulted in severe impairment of its nit rogenase activity, oxygenic photosynthesis, chlorophyll a content and osmotolerance. Among alkali cations only Cs+ or Rb+ restored these phy siological processes to an almost normal level. Parent and mutant were similar with respect to Cs+ or Pb+ uptake and accumulation and also t o regulation by NH4+. The ions Na+ or K+, at much higher concentration , significantly influenced Cs+ uptake and accumulation in both the mut ant and the parent. These findings have important implications for cya nobacteria growing in Cs+-polluted habitats.