The membrane-associated phosphate-specific transporter (Pst) complex is composed of four different proteins: PstS, PstC, PstA and PstB. The PstS component detects and binds Pi with high affinity; the PstA and PstC form transmembrane pores for Pi entry, while PstB provides energy through ATP hydrolysis. In the Mycobacterium tuberculosis genome, four different gene clusters encode three PstS, and two of each of the other sub-units. We used RT-PCR to show that these clusters represent at least three distinct operons. The pstS3-containing operon was the only one induced by lack of environmental Pi. To study the physiologic role of the different PstS sub-units and that of another potential Pi receptor, PknD, we constructed and complemented their knockout (KO) mutants. In Sauton medium, the PstS1-3 KO grew faster than the Wt or the PknD KO. Following 24 h of complete starvation, the PstS3 or PknD deficient strains died if exposed to Pi poor conditions while the PstS1 and PstS2 KO survived and still grew faster than the Wt strain. These results suggest that PstS1-3 may play a role in the regulation of M. tuberculosis growth or metabolism while PstS3 and PknD contribute to the survival of the bacteria in phosphate poor conditions.