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

Abstract

Escherichia coli is a Gram-negative bacterium that colonizes the human intestine and virulent strains can cause severe diarrhoeal and extraintestinal diseases. The protein SslE is secreted by a range of pathogenic and some commensal E. coli strains. It can degrade mucins in the intestine, promotes biofilm maturation and in virulent strains, it is a major determinant of infection, although how it carries out these functions is not well understood. Here we examine SslE from the E. coli Waksman and H10407 strains and show that SslE has a highly dynamic structure in solution. We directly observe acidification within mature biofilms, describe a mechanism where SslE forms unique functional fibres under these conditions and determine that these SslE aggregates can bind cellulose, a major exopolysaccharide of many E. coli biofilms. Our data indicates that the spatial organization of SslE polymers and local pH are critical for biofilm maturation and SslE is a key factor that drives persistence of SslE-secreting bacteria during acidic stress.

How to study biofilms: technological advancements in clinical biofilm research

“…This allows for dynamic growth analysis without having to use a confocal microscope, although this can still be utilised if required. Arguably, one of the major advantages of microfluidic devices is the ability to image the biofilm directly in situ in real-time ( Brown et al., 2019 ; Straub et al., 2020 ; Corsini et al., 2021 ) using a number of different probes and stains at single-cell resolution using confocal microscopy to generate complex images of the biofilm structure and its components. Whilst one advantage is being able to use low inoculation and culture volumes, therefore accommodating small clinical samples, this also comes with small output volumes for downstream sampling.…”

“…The information obtained from z -stack image analysis can provide information on biofilm depth, biomass, and surface area which is useful to compare biofilm characteristics when exposed to different molecules, along with live/dead staining ( Figures 2A, B ) which can show the distribution of bacterial viability within the biofilm ( Bridier et al., 2010 ; Morris et al., 2020 ; Cleaver et al., 2021 ). Specific dyes and probes can be used, such as FM 1-43, fluorescent in situ hybridisation (FISH) probes ( Thurnheer et al., 2004 ; Malic et al., 2009 ; Lebeer et al., 2011 ), and carboxy-SNARF ( Corsini et al., 2021 ) for the monitoring of pH within the biofilm. However, CLSM suffers from photobleaching of samples, therefore the sampling of biofilms over a long period of time becomes a challenge.…”

Characterization of Glycosylation-Specific Systemic and Mucosal IgA Antibody Responses to Escherichia coli Mucinase YghJ (SslE)

“…Through the action of its M60-like aminopeptidase domain (9), YghJ can erode the protective mucus layer that protect mucosal membranes in humans by degrading MUC2, MUC3, and MUC5AC proteins, thus allowing E. coli to reach the epithelial cell surface and start colonization (8,10). There is also evidence that YghJ help mediate E. coli biofilm formation both during colonization (11) as well as when surviving outside the host (12). In enterotoxigenic E. coli (ETEC), YghJ is secreted through T2SS, which also mediates secretion of the ETEC heat-labile toxin (LT) (13).…”