Alterations in carotenoid synthesis accompanying mutation in Corynebacterium michiganense.

Colour mutants of the tomato pathogen, Coynebacterium michiganense, provided an opportunity to determine the nature of this micro-organism's pigments, and the effect of mutation and nutrition thereon. The major pigments of C. michiganense are carotenoids. The parent and mutant strains show distinct qualitative differences in pigment synthesis. The naturally occurring yellow parent type produces cryptoxanthin and lycopene. A pink mutant forms lycopene and spirilloxanthin, A red back-mutant produces only lycopene. An orange mutant synthesizes cryptoxanthin, /?-carotene and canthaxanthin. Carotenoids were not detected in the colourless mutants. Carotenoid synthesis in the yellow strain of C. rnichiganense is affected by thiamine in a manner similar to that previously described for C. poinsettiae: cryptoxanthin and lycopene are synthesized only at relatively high thiamine concentrations. The formation of lycopene, relative to spirilloxanthin, in the pink mutant is favoured by high thiamine concentrations. Similarly, the red strain forms appreciably more lycopene a t higher thiamine concentrations than at lower. The formation of carotenoids in the orange strain appears not to be influenced by external thiamine concentration, possibly because this culture synthesizes an excess of the vitamin. No other nutritional factor which was examined caused detectable alterations in colour of the cells.