The best character-ized of these pathways was first described in Pseduomonas stutzeriWM88 [9], and it is based on a NAD-dependent phosphite oxi-doreductase encoded in the ptxABCDE operon. In the ptx operon,the ptxABC genes encode an ABC-type phosphite transporter, theptxD gene encodes a NAD:phosphite oxidoreductase and ptxE isa transcription factor that shares homology with the LysR familyof transcriptional regulators [9]. The ptxABCDE operon is a com-ponent of the P. stutzeri Pho regulon, which is controlled by atwo-component system formed by PhoB (transcription factor