Molecular and cellular insight into Escherichia coli SslE and its role during biofilm maturation
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 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 E. coli Waksman and H10407 strains and reveal that it has a novel and dynamic structure. In response to acidification within mature biofilms we show how SslE forms a unique functional aggregate that interacts with cellulose and regulates the distribution of exopolysaccharides in macrocolony 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.