Contrasting fates of the paraquat monocation radical in Escherichia coli B and in Dunaliella salina

Anaerobic cultures of Escherichia coli exposed to paraquat (PQ²⁺) accumulated the corresponding monocation radical PQ^{{plus sign, dot below}} both within the cells and in the suspending medium. The green alga, Dunaliella salina, which is susceptible to a light- and O₂-dependent toxicity of PQ²⁺, was nevertheless unable to cause accumulation of PQ^{{plus sign, dot below}}when illuminated anaerobically and could, moreover, discharge the ESR signal and the blue color of PQ^{{plus sign, dot below}} accumulated by E. coli. Spin trapping allowed demonstration of the photoproduction of O^-₂ within D. salina and of the augmentation of that O^-2 production by PQ²⁺. D. salina appears to contain an electron sink and a heat-labile mechanism for transferring electrons from PQ^{{plus sign, dot below}} to that sink. This mechanism was demonstrable anaerobically but did not prevent PQ^{{plus sign, dot below}}-mediated O^-₂ production under aerobic conditions.