Proteolytic activity of surface exposed HtrA determines its expression level and is needed to survive acidic conditions inClostridioides difficile

Abstract

AbstractTo survive in the host, pathogenic bacteria need to be able to react to the unfavourable conditions that they encounter, like low pH, elevated temperatures, antimicrobial peptides and many more. These conditions may lead to unfolding of envelope proteins and this may be lethal. One of the mechanisms through which bacteria are able to survive these conditions is through the protease/foldase activity of the high temperature requirement A (HtrA) protein. The gut pathogenClostridioides difficileencodes one HtrA homolog that is predicted to contain a membrane anchor and a single PDZ domain. The function of HtrA inC. difficileis hitherto unknown but previous work has shown that an insertional mutant ofhtrAdisplayed elevated toxin levels, less sporulation and decreased binding to target cells. Here, we show that HtrA is membrane associated and localized on the surface ofC. difficileand characterize the requirements for proteolytic activity of recombinant soluble HtrA. In addition, we show that the level of HtrA in the bacteria heavily depends on its proteolytic activity. Finally, we show that proteolytic activity of HtrA is required for survival under acidic conditions.