Lethality and mutagenicity inHalobacterium mediterranei caused by N-methyl-N′-nitro-N-nitrosoguanidine

Abstract

Compared withEscherichia coli, Halobacterium mediterranei was highly resistant to the lethal effect of N-methyl-N′-nitro-N-nitrosoguanidine (nitrosoguanidine), but it was sensitive to the mutagenic action of this chemical agent. Nitrosoguanidine at 500 μg ml−1 gave a cell survival level between 1% and 10%, and this allowed us to obtain more Josamycin-resistant mutants compared with lower concentrations, which gave higher survival rates but fewer mutants. The efficiency of the mutagenicity obtained with the nitrosoguanidine treatment was examined under a variety of conditions. The optimal conditions for obtaining Josamycinresistant mutants were achieved by exposing, in darkness and without shaking, a suspension of about 108 log-phase cells to 500 μg nitrosoguanidine in 1 ml of 50 mM modified saline Tris-maleate buffer at pH 7.5, or in 1 ml of 5 mM modified saline Tris-citrate-maleate for 30 min at 37°C.