Interplay between a cytosolic and a cell surface carbonic anhydrase in pH homeostasis and acid tolerance of Leishmania

Leishmania parasites have evolved to endure the acidic phagolysosomal environment within host macrophages. How Leishmania cells maintain near-neutral intracellular pH and proliferate in such proton-rich milieu remains poorly understood. We report here that for thriving in acidic condition Leishmania major relies on a cytosolic and a cell surface carbonic anhydrase viz. LmCA1 and LmCA2. Upon exposure to acidic medium, intracellular pH of the LmCA1+/-, LmCA2+/- and LmCA1+/-: LmCA2+/- mutant strains dropped by varying extents that led to cell cycle delay, growth retardation and morphological abnormalities. Intracellular acidosis and growth defects of the mutant strains could be reverted by genetic complementation or bicarbonate supplementation. When J774A.1 macrophages were infected with the mutant strains, they exhibited much lowered intracellular parasite burdens than their wild type counterpart. However, these differences in intracellular parasite burden between the wild type and mutant strains were abrogated if, prior to infection, the macrophages were treated with chloroquine to alkalize their phagolysosomes. Taken together, our results demonstrated that haploinsufficiency of LmCA1 and/or LmCA2 renders the parasite acid-susceptible, thereby unravelling a carbonic anhydrase-mediated pH homeostatic circuit in Leishmania cells.