3 years ago

Conditional Function of Autoaggregative Protein Cah and Common cah Mutations in Shiga Toxin-Producing Escherichia coli.

Matthew R Moreau, Vivek Kapur, Robab Katani, Indira T Kudva, Michelle Qiu Carter, Maria T Brandl
Cah is a calcium-binding autotransporter protein involved in autoaggregation and biofilm formation. Although cah is widespread in Shiga toxin-producing Escherichia coli (STEC), we detected mutations in cah at a frequency of 31.3% in this pathogen. In STEC O157:H7 super-shedder strain SS17, a large deletion results in a smaller coding sequence, lacking the C-terminal 71 amino acids compared with Cah in STEC O157:H7 strain EDL933. We examined the function of Cah in biofilm formation and host colonization to better understand selective pressures for cah mutations. EDL933-Cah played a conditional role in biofilm formation in vitro: it enhanced E. coli DH5α biofilm formation on glass surfaces under agitated culture conditions that prevented autoaggregation, but inhibited biofilm formation under hydrostatic conditions that facilitated autoaggregation. This function appeared to be strain-dependent since Cah-mediated biofilm formation was diminished when an EDL933-cah was expressed in SS17. Deletion of cah in EDL933 enhanced bacterial attachment to spinach leaves and altered the adherence pattern of EDL933 to bovine recto-anal junction squamous epithelial (RSE) cells. In contrast, in trans-expression of EDL933-cah in SS17 increased its attachment to leaf surfaces, and in DH5α, enhanced its adherence to RSE cells. Hence the ecological function of Cah appears to be modulated by environmental conditions and other bacterial strain-specific properties. Considering the prevalence of cah in STEC and its role in attachment and biofilm formation, cah mutations might be selected in ecological niches where inactivation of Cah would result in an increased fitness in STEC during colonization of plants or animal hosts.ImportanceShiga toxin-producing Escherichia coli (STEC) harbors genes encoding diverse adhesins and many of these are known to play an important role in bacterial attachment and host colonization. We demonstrated here that the autotransporter protein Cah confers E. coli DH5α cells with a strong autoaggregative phenotype that is inversely correlated with its ability to form biofilms, and plays a strain-specific role in plant and animal colonization by STEC. Although cah is widespread in the STEC population, we detected a mutation rate of 31.3% in cah, which is similar to that reported in rpoS and in fimH. Formation of cell aggregates due to increased bacteria-to-bacteria interactions may be disadvantageous to bacterial populations under conditions that favor a planktonic state in STEC. Therefore, loss-of-function mutation in cah is likely a selective trait in STEC when autoaggregative properties become detrimental to bacterial cells, and may contribute to the adaptability of STEC to fluctuating environments.

Publisher URL: http://doi.org/10.1128/AEM.01739-17

DOI: 10.1128/AEM.01739-17

You might also like
Discover & Discuss Important Research

Keeping up-to-date with research can feel impossible, with papers being published faster than you'll ever be able to read them. That's where Researcher comes in: we're simplifying discovery and making important discussions happen. With over 19,000 sources, including peer-reviewed journals, preprints, blogs, universities, podcasts and Live events across 10 research areas, you'll never miss what's important to you. It's like social media, but better. Oh, and we should mention - it's free.

  • Download from Google Play
  • Download from App Store
  • Download from AppInChina

Researcher displays publicly available abstracts and doesn’t host any full article content. If the content is open access, we will direct clicks from the abstracts to the publisher website and display the PDF copy on our platform. Clicks to view the full text will be directed to the publisher website, where only users with subscriptions or access through their institution are able to view the full article.