SUMMARY: Sixty different isolates of methionineless auxotrophs of were arranged in nine biochemical groups according to their growth responses to methionine or its precursors. These requirements suggested that possesses a route for methionine biosynthesis which is similar to the pathway operating in and In contrast to findings with the latter organisms syntrophism was not observed between these mutants of even with sonically disrupted potential feeder strains. Two methionineless auxotrophs of fed auxotrophs of which had metabolic blocks earlier in this pathway. These results, which suggested an inability of methionineless auxotrophs of to accumulate precursors of metabolic blocks, were confirmed by a quantitative comparison of methionine precursors in wild-type and mutant strains of and The presence of -methylcysteine (SMC) was demonstrated in wild-type and methionineless auxotrophs of and The growth responses of methionineless auxotrophs of to SMC supported a hypothesis for the participation of this amino acid in the synthesis of methionine via an alternative route.


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