Identification of Membrane-Bound Lytic Murein Transglycosylase A (MltA) as a Growth Factor for in a Silkworm Infection Model.

, the causative agent of tularemia, is transmitted by arthropod vectors within mammalian hosts. The detailed mechanisms contributing to growth and survival of within arthropod remain poorly understood. To identify novel factors supporting growth and survival of within arthropods, a transposon mutant library of subsp. () was screened using an -silkworm infection model. Among 750 transposon mutants screened, the -encoding membrane-bound lytic murein transglycosylase A (MltA) was identified as a novel growth factor of in silkworms. Silkworms infection with an deletion mutant (Δ) resulted in a reduction in the number of bacteria and prolonged survival. The Δ strain exhibited limited intracellular growth and cytotoxicity in BmN4 silkworm ovary cells. Moreover, the Δ strain induced higher expression of the antimicrobial peptide in silkworms compared to the wild-type strain. These results suggest that MltA contributes to the survival of in silkworms immune suppression-related mechanisms. Intracellular growth of the Δ strain was also reduced in human monocyte THP-1 cells. These results also suggest the contribution of MltA to pathogenicity in humans and utility of the -silkworm infection model to explore infection.