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