Isolation and characterization of a metronidazole tolerant mutant of the cyanobacterium Spirulina platensis exhibiting multiple stress tolerance

Mutant cells of Spinulina platensis isolated after chemical mutagenesis (NTG treatment) exhibited approximately three-fold higher tolerance to metronidazole and DCMU (3,4-dichlorophenyl-1, 1-dimethylurea) as compared with wild-type cells. At the same time, mutant cells exhibited a several-fold higher tolerance to supra-high irradiance (38 W/m(2)) than the wild-type, a further response involving Hill reaction activity in the mutant towards the supra-high irradiance mechanism which enabled the mutant cells to withstand the high light intensities. The metronidazole and DCMU tolerance in the mutant cells could not be obviously attributed to lower rates of growth and photosynthesis as suggested previously. A typical coiling pattern in the mutant cells might result in a reduction of exposed surface area, thereby restricting entry of the above toxins. The mutant strains exhibiting tolerance to multiple stresses are potentially useful for application under field conditions.