Biosynthesis of Ergothioneine from Endogenous Hercynine in Mycobacterium smegmatis

Abstract

Ergothioneine was synthesized and accumulated in growing cultures of M. smegmatis when the medium was adequately supplied with S. In a low''s medium, the accumulation was sharply limited although growth of the organism was apparently normal. Synthesis of hercynine, the precursor of ergothioniene, was unaffected by low S levels and was markedly increased by addition of L-histidine, the precursor of hercynine. Resting-cell pellicle experiments, performed with cells grown on the low S high histidine medium showed that ergothioniene was synthesized from endogenous hercynine when cysteine or compounds readily converted to cysteine (such as cystine, lanthionine, cystathionine and thiazojidine carboxylic acid) were added. Homocysteine and djenkolic acid allowed for minimal synthesis of betaine, whereas methionine, S-methylcysteine, NASO4, and sodium thiosulfate were unable to donate S for ergothioniene synthesis under the experimental conditions employed. Addition of cysteine to a resting pellicle preparation caused the formation of 100 to 200 [mu]g of ergo-thioneine/g of dry cells in 2.5 to 3 hr. A modified procedure for isolating ergothioneine and hercynine, employing a 75% ethyl alcohol extraction of wet organisms, followed by a single alumina column separation of the compounds, is described.