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A scotochromogenic acid-fast bacillus was isolated from a lymph node of a 2-year-old female. On the basis of conventional testing, the mycobacterium appeared to be Mycobacterium scrofulaceum. Its mycolic acid profile, however, was not identical to that of Mycobacterium scrofulaceum but was similar to that of Mycobacterium interjectum. Direct sequencing of the 16S rRNA gene revealed a unique nucleic acid sequence, suggesting that the isolate represents a previously undescribed pathogenic species.

N-methyl-N-nitroso-N′-nitroguanidine was used for the induction of two types of mutations in the PN strain ofMycobacterium phlei. Nineteen auxotrophic, 136 scotochromogenic and 50 achromogenic mutants were isolated after of treatment with nitrosoguanidine at a concentration of 1,000 μg/ml. Auxotrophic mutants required primarily amino acids and vitamins and half of them may be used for further genetic work due to their low frequency of spontaneous reversions. Colonies of scotochromogenic mutants were orange with the exception of one, which was strawberry red. Most scotochromogenic mutants were detected on a streptomycin containing medium. Roughly two thirds of the scotochromogenic mutants and one half of achromogenic mutants did not revert to the original photochromogenic character.

A red, scotochromogenic mutant of the non-acid-fast strain ofMycobacterium phlei was obtained. Mutual relationship between this mutant and rapidly growing mycobacteria was studied using complex morphological, cultivation, biochemical and serological analyses as well as determination of the base composition in DNA. Taxonomical aspects of individual analyses are discussed.

Five scotochromogenic mutants and 11 achromogenic mutants were induced by UV irradiation of the non-acid-fast photochromogenic PN strain ofMycobacterium phlei. Spontaneous scotochromogenic and achromogenic mutants were not obtained. Colonies of the scotochromogenic mutants are orange, except for one mutant which is ochre. Three mutants are resistant to STM. Out of 11 achromogenic mutants 3 were induced by UV treatment of the original photochromogenic strain, 8 were prepared from the scotochromogenic mutant. No significant differences in the sensitivity to UV rays were found among the scotochromogenic mutant, achromogenic mutant and the photochromogenic PN strain ofMycobacterium phlei under the given experimental conditions. Scotochromogenic mutants and most achromogenic mutants are stable and suitable for further genetic investigation. Pigmentation changes can be used as genetic marker in mutation studies.

N-Methyl-N-nitrosourea was used to induce auxotrophic, scotochromogenic and isonicotinic acid hydrazide resistant mutants inMycobacterium phlei and its effect was compared with that of nitrosoguanidine. Seventeen auxotrophic mutants requiring arnino acids or vitamins and 52 sootochromosgenic mutants with orange colonies were induced. The frequency of isonicotinic acid hydrazide-resistant mutants increased by two orders of magnitude.