Screening Leishmania donovani-specific genes required for visceral infection.

Comparison of the Leishmania infantum genome with Leishmania braziliensis and Leishmania major genomes has identified 25 L. infantum species-specific genes that are absent or pseudogenes in L. major and L. braziliensis. To determine whether these L. infantum species-specific genes are involved in visceral Leishmania infection, we cloned the orthologues of 14 L. infantum species-specific genes from the genetically closely related Leishmania donovani and introduced them into L. major. Two of these L. donovani species-specific genes were found to significantly increase L. major survival in visceral organs in BALB/c mice. One (orthologue of LinJ28_V3.0340; Ld2834) of these two genes was further investigated. The L. donovani Ld2834 null mutants displayed dramatically reduced virulence in BALB/c mice and were unable to survive in axenic amastigote culture conditions arguing that Ld2834 plays a crucial role in enabling L. donovani survive at the increased temperature typically associated with visceral organs. Ld2834 encodes a 50 kDa protein that is localized in the cytoplasma and has no significant sequence similarity with other known genes. This study validates the importance of comparative genomics for understanding Leishmania species pathology and argues that Leishmania species-specific genes play important roles in tissue tropism and virulence.