Influence of csgD and ompR on Nanomechanics, Adhesion Forces, and Curli Properties of E. coli

Abstract

Curli are bacterial appendages involved in the adhesion of cells to surfaces; their synthesis is regulated by many genes such as csgD and ompR. The expression of the two curli subunits (CsgA and CsgB) in Escherichia coli (E. coli) is regulated by CsgD; at the same time, csgD transcription is under the control of OmpR. Therefore, both genes are involved in the control of curli production. In this work, we elucidated the role of these genes in the nanomechanical and adhesive properties of E. coli MG1655 (a laboratory strain not expressing significant amount of curli) and its curli-producing mutants overexpressing OmpR and CsgD, employing atomic force microscopy (AFM). Nanomechanical analysis revealed that the expression of these genes gave origin to cells with a lower Young's modulus (E) and turgidity (P0), whereas the adhesion forces were unaffected when genes involved in curli formation were expressed. AFM was also employed to study the primary structure of the curli expressed through the freely jointed chain (FJC) model for polymers. CsgD increased the number of curli on the surface more than OmpR did, and the overexpression of both genes did not result in a greater number of curli. Neither of the genes had an impact on the structure (total length of the polymer and number and length of Kuhn segments) of the curli. Our results further suggest that, despite the widely assumed role of curli in cell adhesion, cell adhesion force is also dictated by surface properties because no relation between the number of curli expressed on the surface and cell adhesion was found.

Pellicle formation by Escherichia coli K-12: Role of adhesins and motility

“…It should be noted that previous studies have found that the pT7-CsgD plasmid induces biofilm production in E. coli K-12 at least as well as the ompR234 allele (28,31,43). Overexpression of curli in MC4100 via pT7-CsgD permitted pellicle formation in shaking conditions despite lack of motility, although pellicle formation was severely hindered when compared to PHL644 (motile) and PHL644h (hypermotile).…”

“…Initial work focused on generating a robust, recombinant Escherichia coli K-12 biofilm capable of biocatalysis (29,30,31). We grew a biofilm-forming strain of E. coli K-12, PHL644, a variant of MC4100 with a mutation in the ompR gene (ompR234) resulting in increased curli expression (23), in conditions conducive to biofilm formation (M63+ minimal medium, 30 °C, and orbital shaking at 70 rpm).…”

Temperature-Dependent Influence of FliA Overexpression on PHL628 E. coli Biofilm Growth and Composition

“…Our future studies will also include an examination of the anti-sigma factor FlgM, a small protein that binds to FliA, inhibiting FliA binding to DNA, and its role in creating negative feedback loops that might be tempering the overexpression response of FliA (Park et al, 2001;Barembruch and Hengge, 2007). FlgM expression is induced by FliA and is inhibited by CsgD, a transcriptional regulator that has its own transcription regulated by OmpR, a protein that is constitutively active in PHL628 cells (Dudin et al, 2014;Perni et al, 2016). This complex network of interactions could explain both the tempered nature of our CLSM and biochemical results, despite exogenous overexpression of FliA.…”

Low‐Field Actuating Magnetic Elastomer Membranes Characterized using Fibre‐Optic Interferometry

“…Mechanical Characterization: Young's modulus measurements of the ME membranes were carried out through nanoindentation according to a published method by Polina Prokopovich et.al. [33] Briefly, an atomic force microscope (AFM, XE-100, Park Systems, South Korea) was employed for adhesion force measurements using a cantilever (Veeco, ORC8-10, tip radius of 15 nm, nominal spring constant K cantilever of 0.05 Nm -1 ). Therefore, Young's modulus of the samples was calculated by following the formula:…”