AUTHOR=Nakamura Takemasa , Shimizu Takashi , Inagaki Fumiya , Okazaki Shoma , Saha Shib Shankar , Uda Akihiko , Watanabe Kenta , Watarai Masahisa 

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

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=10

YEAR=2021

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2020.581864

DOI=10.3389/fcimb.2020.581864

ISSN=2235-2988

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