The adjacent ATP-binding protein-encoding genes of the phosphate-specific transport () locus have non-overlapping cellular functions.

UNLABELLED

The widely conserved operon encodes a low-velocity, high-affinity, ATP-dependent importer for inorganic phosphate (Pi). The gene encodes the ATPase that powers the import of Pi into the cell. In some Firmicutes, including the gastrointestinal commensal and opportunistic pathogen , the locus contains adjacent genes. In this work, we compared the functionality of and and share sequence similarities with verified PstB ATPases from and and only share ~60% amino acid identity with each other. Deletion of was associated with a growth defect in low Pi-containing chemically defined medium (CDM), reduced Pi uptake, and a moderate increase in alkaline phosphatase (AP) activity. Deletion of fully inhibited growth in CDM regardless of inorganic phosphorus source but did not hinder growth in rich, undefined medium. The Δ mutant also exhibited a significant increase in AP activity that was associated with extracellular Pi accumulation. Overexpression of in the mutant was sufficient to restore growth in low-Pi CDM, Pi uptake, and AP activity, but this was not recapitulated with overexpression of in the Δ mutant. Deletion of either paralog increased expression of the tandem paralog, and overexpression of in Δ reduced expression. These results suggest that the -encoded ATPase is required for Pi import, while the -encoded ATPase has an accessory role in Pi import that can be duplicated by the presence of excess PstB2.

IMPORTANCE

Phosphate is critical for all microbial life. In many bacteria, inorganic phosphate (Pi) is imported by the high-affinity, low-velocity Pst-PhoU system. The gene encodes the ATPase that powers Pi import. The operon in many Firmicutes, including the human commensal and opportunistic pathogen , contains adjacent genes, and . No studies on the relative biological contributions of tandem paralogs in any microbe have been published. This genetic study indicates that and do not have equivalent functions. The gene encodes an ATPase that is required for Pi import, while the ATPase encoded by has an accessory role in Pi import that can be duplicated by the presence of excess PstB2.