FIGURE 1: Existing gaps in our current knowledge of PBP3_SAL function in S. Typhimurium. (A) Phenomena to be analysed in future studies respect PBP3_SAL activity during the interaction of S. Typhimurium with the eukaryotic cell. These include: (1) the regulators that upregulate expression of PBP3_SAL following entry into the phagosomal compartment; (2) whether intracellular bacteria express PBP3 in the acidic phagosome and, in that case, if it is co-expressed with PBP3_SAL; (3) how PBP3_SAL expression is downregulated when bacteria exit from the infected host cell to the extracellular space; and, (4) given the specialization of PBP3_SAL for functioning exclusively in acidic environments, whether there are additional differences in the PG machinery of intra-phagosomal and cytosolic bacterial populations that could result in a PG structural alterations; (B) Aspects that at the bacterial cell level that remain unknown for PBP3_SAL, including: (5) the exact localization of PBP3_SAL on the bacterial surface; and, (6) the interaction of PBP3_SAL with divisome proteins required to build a division septum independently of PBP3.