Bordetella bronchiseptica Bcr4 antagonizes the negative regulatory function of BspR by its role in the type III secretion

AbstractBordetella species, includingB. pertussis, have a type III secretion system that is highly conserved among Gram ‐negative pathogenic bacteria. Genes encoding the component proteins of a type III secretion system are localized at thebsc locus in theBordetella genome. Here we investigated the function of a hypothetical protein Bcr4 encoded at thebsc locus in theB. bronchiseptica genome. We created a Bcr4 ‐deficient mutant and determined the amounts of type III secreted proteins (e.g., BopB, BopN, and Bsp22) in both the supernatant fraction and whole‐cell lysates of the Bcr4‐deficient mutant. The levels of these proteins were significantly lower than those of the wild‐type strain. In a Bcr4‐ overproducing strain, the amounts of type III secreted proteins in the supernatant fraction and whole‐cell lysates were greatly increased compared to those of the wild‐type strain. The type III secreted protein BspR was reported to negatively regulate the type III secretion system. Here, we used a Bcr4+BspR double‐knockout mutant, and we observed that this mutant did not secrete the type III secreted proteins, whereas the levels of the proteins in whole‐cell lysates of this mutant were nearly equal to those in whole‐cell lysates of the BspR‐deficient mutant. Bcr4 thus appears to pl ay an essential role in the extracellular secretion of type III secreted proteins. Our data also suggest that Bcr4 antagonizes the negative regulatory function of BspR.

Source: Microbiology and Immunology - November 8, 2018 Category: Microbiology Authors: Ryutaro Nishimura, Akio Abe, Yusuke Sakuma, Asaomi Kuwae Tags: Original Article Source Type: research