Molecular and cellular insight into Escherichia coli SslE and its role during biofilm maturation

Paula M Corsini,W Trent Franks,Charlotte J C Edwards-Gayle,Pau Bernadó,Leanne Cleaver,James A Garnett,Vidya C Darbari,Katherine Fenn,Steven Lynham,Lee Sewell ,James A Jarvis ,Michael A Curtis ,Guy Carpenter ,Amin Sagar,Slobodan Sirovica,Dinu Iuga,Sunjun Wang,Saima Rehman,Giulia Mastroianni,Ben Dorgan

doi:10.1038/s41522-022-00272-5

Abstract

Escherichia coli is a Gram-negative bacterium that colonises the human intestine and virulent strains can cause severe diarrhoeal and extraintestinal diseases. The protein SslE is secreted by a range of pathogenic and commensal E. coli strains. It can degrade mucins in the intestine, promotes biofilm maturation and it is a major determinant of infection in virulent strains, although how it carries out these functions is not well understood. Here, we examine SslE from the commensal E. coli Waksman and BL21 (DE3) strains and the enterotoxigenic H10407 and enteropathogenic E2348/69 strains. We reveal that SslE has a unique and dynamic structure in solution and in response to acidification within mature biofilms it can form a unique aggregate with amyloid-like properties. Furthermore, we show that both SslE monomers and aggregates bind DNA in vitro and co-localise with extracellular DNA (eDNA) in mature biofilms, and SslE aggregates may also associate with cellulose under certain conditions. Our results suggest that interactions between SslE and eDNA are important for biofilm maturation in many E. coli strains and SslE may also be a factor that drives biofilm formation in other SslE-secreting bacteria.

Highlights

Escherichia coli is a primary coloniser of the lower intestinal tract of humans and other warm‐blooded animals
While many strains are considered beneficial to the host and help to maintain a healthy immune system, virulent strains are the cause of severe diarrhoeal diseases, including haemorrhagic colitis, and extraintestinal diseases, such as neonatal meningitis, urinary tract infections, sepsis and pneumonia[1]
To understand the role of SslE in E. coli biofilms, we first initiated a structural analysis of recombinant SslE from E. coli W, minus the N-terminal lipidation motif and adjacent disordered region (Fig. 1a)

Summary

Introduction

Escherichia coli is a primary coloniser of the lower intestinal tract of humans and other warm‐blooded animals. While many strains are considered beneficial to the host and help to maintain a healthy immune system, virulent strains are the cause of severe diarrhoeal diseases, including haemorrhagic colitis, and extraintestinal diseases, such as neonatal meningitis, urinary tract infections, sepsis and pneumonia[1]. A wide range of pathogenic E. coli strains, and some commensals, use a Vibrio-like type II secretion system (T2SS) to translocate the protein SslE across their outer membrane and onto their extracellular surface[2–7]. These include the Waksman (W), enterotoxigenic (ETEC), enterohemorrhagic (EHEC), enteropathogenic (EPEC), enteroaggregative (EAEC), enteroinvasive (EIEC) and neonatal meningitis E. coli (NMEC) strains. SslE is required for full virulence in a rabbit model of EPEC infection[4] and as a surface-exposed antigen, SslE has shown great promise as a broadly protective vaccine candidate against a wide range of E. coli pathotypes[3,6,8,9].

Methods

Results

Conclusion