AUTHOR=Nguyen Yen Thi Hai , Kim Chaewon , Kim Yuri , Jeon Kyeongseok , Kim Hong-il , Ha Na-Young , Cho Nam-Hyuk 

TITLE=The Orientia tsutsugamushi ScaB Autotransporter Protein Is Required for Adhesion and Invasion of Mammalian Cells

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.626298

DOI=10.3389/fmicb.2021.626298

ISSN=1664-302X

ABSTRACT=<p>Autotransporter proteins are widely present in Gram-negative bacteria. They play a pivotal role in processes related to bacterial pathogenesis, including adhesion, invasion, colonization, biofilm formation, and cellular toxicity. Bioinformatics analysis revealed that <italic>Orientia tsutsugamushi</italic>, the causative agent of scrub typhus, encodes six different autotransporter genes (<italic>scaA</italic>–<italic>scaF</italic>). Although four of these genes (<italic>scaA</italic>, <italic>scaC</italic>, <italic>scaD</italic>, and <italic>scaE</italic>) are present in diverse strains, <italic>scaB</italic> and <italic>scaF</italic> have been detected in only a limited number of strains. Previous studies have demonstrated that ScaA and ScaC are involved in the adherence of host cells. However, the putative function of other <italic>O. tsutsugamushi</italic> Sca proteins has not been studied yet. In this study, we show that <italic>scaB</italic> is transcribed and expressed on the surface of <italic>O. tsutsugamushi</italic> Boryong strain. Using a heterologous <italic>Escherichia coli</italic> expression system, we demonstrated that ScaB-expressing <italic>E. coli</italic> can successfully mediate adherence to and invasion into non-phagocytic cells, including epithelial and endothelial cells. In addition, pretreatment with a recombinant ScaB polypeptide inhibits the entry of <italic>O. tsutsugamushi</italic> into cultured mammalian cells. Finally, we also identified the <italic>scaB</italic> gene in the Kuroki and TA686 strains and observed high levels of sequence variation in the passenger domains. Here, we propose that the ScaB protein of <italic>O. tsutsugamushi</italic> can mediate both adhesion to and invasion into host cells in the absence of other <italic>O. tsutsugamushi</italic> genes and may play important roles in bacterial pathogenesis.</p>