Growth of Nostoc muscorum mutants in the presence of diuron (DCMU) and L-methionine-DL-sulfoximine

Summary

Diuron (DCMU) is inhibitory to the photoautotrophic and photoheterotrophic growth of the N₂-fixing blue-green algaNostoc muscorum at concentrations of 1.0×10⁻⁵ M and 2.0×10⁻⁵ M, respectively. A mutant of this organism resistant to 5.0×10⁻⁵ M DCMU under its photoheterotrophic growth conditions, with the ability to utilize DCMU as a carbon and nitrogen source for growth, and complete inability to grow photoautotrophically has been isolated. With the apparent defect in its photosynthetic ability, it is suggested that theDCMU ^r mutant lacks the step inhibited by 1.0×10⁻⁵ M DCMU, and metabolizes DCMU by an existing enzyme system in the absence of such inhibition. That this enzyme may be glutamine synthetase (GS) is explained with the help of a L-methionine-DL-sulfoximine (MSO)-resistant mutant ofN. muscorum which is able to grow faster with 2.0×10⁻⁵ DCMU and is known to contain an altered GS.