A Novel Calcium Uptake Transporter of Uncharacterized P-Type ATPase Family Supplies Calcium for Cell Surface Integrity in Mycobacterium smegmatis

Ca(2+) plays an important role in the physiology of bacteria. Intracellular Ca(2+) concentrations are tightly maintained in the nanomolar range. Molecular mechanisms of Ca(2+) uptake in bacteria remain elusive. Here we show that CtpE is responsible for Ca(2+) uptake in Mycobacterium smegmatis. It represents a previously uncharacterized P-type ATPase family in bacteria. Disruption of ctpE in M. smegmatis resulted in a mutant with impaired growth under Ca(2+)-deficient conditions. The growth defect of the mutant could be rescued by Ca(2+) or by ectopic expression of ctpE from M. smegmatis or the orthologous gene (Rv0908) from Mycobacterium tuberculosis H37Rv. Radioactive transport assays revealed that CtpE is a Ca(2+)-specific transporter. Ca(2+) deficiency increased expression of ctpE, resulting in increased (45)Ca(2+) accumulation in cells. ctpE is a gene that is part of an operon, which is negatively regulated by Ca(2+). The ctpE mutant also showed hypersensitivity to polymyxin B, increased biofilm formation, and higher cell aggregation, indicating cell envelope defects. Our work establishes, for the first time, the presence of Ca(2+) uptake pumps of the energy-dependent P-type ATPase superfamily in bacteria and also implicates that intracellular Ca(2+) is essential for growth and cell envelope integrity in M. smegmatis.