A direct sulfhydrylation pathway is used for methionine biosynthesis in Pseudomonas aeruginosa.

The relationship between genes and enzymes in the methionine biosynthetic pathway has been studied in Pseudomonas aeruginosa. The first step is catalysed by an O-succinylhomoserine synthase, the product of the metA gene mapped at 20 min on the chromosome. The second step is achieved by direct sulfhydrylation, involving the enzyme encoded by a metZ gene that we have identified and sequenced, located at 40 min. Thus Pseudomonas appears to be the only organism so far described that uses O-succinylhomoserine as substrate for a direct sulfhydrylation. As in yeast, the two transsulfuration pathways between cysteine and homocysteine, with cystathionine as an intermediate, probably exist in parallel in this organism.