SUMMARY: When an Arg- mutant of was grown on sucrose-nitrate agar supplemented with L-citrulline, it produced only non-sporulating aerial mycelia. Sporulation could be induced by adding 0.1 to 10.0 mM-L-methionine or 0.01 mM-cyanocobalamin; several other compounds including homocysteine, other amino acids, vitamins and precursors of nucleic acids were ineffective. Growth of the mutant did not differ significantly with or without methionine. The mutant was more sensitive to L-norleucine (a methionine analogue) than the parent strain. Spontaneous mutants, resistant to this analogue, were obtained. They all sporulated well without exogenously added methionine. In medium-exchange experiments, methionine was required for sporulation only after 48 h cultivation. The phenomenon reported here is most probably based on partially impaired methionine biosynthesis caused by an as yet uncharacterized non-auxotrophic mutation, since Arg revertants retained their methionine requirement for sporulation, and were also sensitive to L-norleucine.


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