A conserved protein, BcmA, mediates motility, biofilm formation, and host colonisation in Adherent InvasiveEscherichia coli

Abstract

25Adherent Invasive Escherichia coli (AIEC) is a non-diarrhoeagenic intestinal E. coli pathotype 26 associated with Crohn's Disease. AIEC pathogenesis is characterised by biofilm formation, 27 adhesion to and invasion of intestinal epithelial cells, and intracellular replication within 28 epithelial cells and macrophages. Here, we identify and characterise a protein in the 29 prototypical AIEC strain LF82 which is required for efficient biofilm formation and dispersal -30 LF82_p314. LF82 ΔLF82_314 have defective swimming and swarming motility, indicating 31 LF82_p314 is important for flagellar-mediated motility, and thus surface colonisation and 32 biofilm dispersal. Flagellar morphology and chemotaxis in liquid appear unaffected by 33 deletion of LF82_314, suggesting LF82_p314 does not elicit an effect on flagella biogenesis or 34 environmental sensing. Flagellar motility has been implicated in AIEC virulence, therefore we 35 assessed the role of LF82_p314 in host colonisation using a Caenorhabditis elegans model. 36 We found that LF82 ΔLF82_314 have an impaired ability to colonise the C. elegans compared 37 to wild-type LF82. Phylogenetic analysis showed that LF82_314 is conserved in several major 38 enterobacterial pathogens, and suggests the gene may have been acquired horizontally in 39 several genera. Our data suggests LF82_p314 may be a novel component in the flagellar 40 motility pathway and is a novel determinant of AIEC colonisation. Our findings have potential 41 implications not only for the pathogenesis of Crohn's Disease, but also for the course of 42 infection in several major bacterial pathogens. We propose a new designation for LF82_314, 43 biofilm coupled to motility A, or bcmA. 44 Author summary 45 Adherent Invasive Escherichia coli (AIEC) are a group of bacteria implicated in the 46 pathogenesis of Crohn's Disease, a chronic inflammatory bowel disease with no cure. Critical 47 48 colonise the host surface using specialised, propeller-like appendages called flagella. In this 49 paper, we describe a novel protein -LF82_p314 (BcmA) -which is required for efficient 50 flagella-mediated motility and surface colonisation in AIEC. Using a nematode worm 51 (Caenorhabditis elegans) infection model, we show that LF82_p314 enables effective 52 colonisation of the C. elegans gut, suggesting a role for the protein during human infection. 53 These findings indicate BcmA is significant for initial colonisation of the human gut by AIEC, 54 and therefore the onset of Crohn's Disease. 55 Introduction 56 Crohn's Disease (CD) is a chronic and relapsing inflammatory bowel disease presenting with 57 frequent bloody diarrhoea, bowel obstruction, abdominal pain, and extraintestinal 58 manifestations affecting the eyes, skin, joints, and liver (reviewed in [1-3]). CD is a complex 59 syndrome which is understood as an unchecked and inappropriate inflammatory response to 60 intestinal bacteria, potentiated by carriage of one or several of over 180 predisposing 61 immune-related alleles [4-13] and their inter...