Characteristics of a caesium-resistant (Cs⁺-R) mutant of the N₂-fixing cyanobacterium Nostoc muscorum: dependence on Cs⁺ or Rb⁺ for normal diazotrophy and osmotolerance

Abstract

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