FimC binds to the promoter region of <i>agn43</i> to modulate autoaggregation.

Abstract

<h4>Background</h4>Avian pathogenic <i>Escherichia coli</i> (APEC) infection causes high mortality in chicks and leads to significant economic losses in the poultry industry. During the initial infection, APEC colonizes host cells using type 1 fimbriae and subsequently forms biofilms, resulting in persistent and chronic infections. <i>fimC</i> is a chaperone protein associated with type 1 fimbriae and plays a crucial role in the assembly of fimbriae. However, its regulatory role in <i>agn43</i>-mediated autoaggregation remains unclear.<h4>Methods</h4>By constructing <i>fimC</i> gene mutant strains, the autoaggregation, motility, biofilm formation, and the adhesion and invasion ability to HD-11 cells were examined. The transcriptome and the electrophoretic mobility shift assay (EMSA) were used to screen and verify the regulation of <i>fimC</i> on downstream genes.<h4>Results</h4>The results demonstrated that the lack of <i>fimC</i>, but not fimbriae, significantly increased autoaggregation (<i>p</i> < 0.001) while promoting the transcription of <i>agn43</i> (<i>p</i> < 0.01). Transcriptomic analysis showed that the deletion of <i>fimC</i> caused significant changes in the gene transcription levels in a variety of pathways, such as flagellar synthesis, biofilm formation, quorum sensing, and bis-(3'-5')-cyclic diguanylic acid (c-di-GMP) metabolism. Further investigation revealed that <i>fimC</i> directly interacted with the promoter region of <i>agn43</i> and inhibited its transcription. In addition, both <i>fimC</i> and <i>agn43</i> had regulatory effects on biofilm formation, motility, adhesion, and invasion.<h4>Conclusion</h4>This study demonstrated that <i>fimC</i> acts as an atypical DNA-binding protein to regulate the transcription of <i>agn43</i>. It also highlights the importance of <i>fimC</i> in the biofilm formation and adhesion ability of APEC, which provides new insights into the functions of the fimbrial chaperone protein <i>FimC</i>.