Rhizobium melilotimutants defective in thephoCDET-encoded phosphate transport system form root nodules on alfalfa plants that fail to fix nitrogen (Fix−). We have previously reported that two classes of second-site mutations can suppress the Fix−phenotype ofphoCDETmutants to Fix+. Here we show that one of these suppressor loci (sfx1) contains two genes,orfAandpit, which appear to form an operon transcribed in the orderorfA-pit. The Pit protein is homologous to various phosphate transporters, and we present evidence that three suppressor mutations arose from a single thymidine deletion in a hepta-thymidine sequence centered 54 nucleotides upstream of theorfAtranscription start site. This mutation increased the level oforfA-pittranscription. These data, together with previous biochemical evidence, show that theorfA-pitgenes encode a Pitransport system that is expressed in wild-type cells grown with excess Pibut repressed in cells under conditions of Pilimitation. InphoCDETmutant cells,orfA-pitexpression is repressed, but this repression is alleviated by the second-site suppressor mutations. Suppression increasesorfA-pitexpression compensating for the deficiencies in phosphate assimilation and symbiosis of thephoCDETmutants.