Characteristics of a stable, filamentous mutant of a coccoid blue-green alga.

Filamentous mutants were induced in a coccoid blue-green alga, Agmenellum quadruplicatum strain BG1, after treatment with N-methyl-N'-nitro-N-nitrosoguanidine (NTG). The mutants fall into two general classes: filaments with cross walls and filaments without cross walls. All mutants of these general types derived from BG1 are stable and have growth rates the same as or very similar to the wild type under a variety of conditions. Detailed examination of one mutant, 53SB2, revealed no difference in deoxyribonucleic acid content nor in base ratios. Mutant 53SB2 did not revert to the normal cell size and shape when grown under different physical conditions nor upon the addition of potential reversing agents to the basal medium. It is our general experience that filamentous mutants such as those described here in BG1 are commonly induced in other coccoid blue-green algae after NTG treatment.