Surface proteins and the formation of biofilms by Staphylococcus aureus

Abstract

Staphylococcus aureus biofilms pose a serious clinical threat as reservoirs for persistent infections. Despite this clinical significance, the composition and mechanism of formation of S. aureus biofilms are unknown. To address these problems, we used solid-state NMR to examine S. aureus (SA113), a strong biofilm-forming strain. We labeled whole cells and cell walls of planktonic cells, young biofilms formed for 12-24h after stationary phase, and more mature biofilms formed for up to 60h after stationary phase. All samples were labeled either by (i) [N]glycine and l-[1-C]threonine, or in separate experiments, by (ii) l-[2-C,N]leucine. We then measured C-N direct bonds by C{N} rotational-echo double resonance (REDOR). The increase in peptidoglycan stems that have bridges connected to a surface protein was determined directly by a cell-wall double difference (biofilm REDOR difference minus planktonic REDOR difference). This procedure eliminates errors arising from differences in N isotopic enrichments and from the routing ofC label from threonine degradation to glycine. For both planktonic cells and the mature biofilm, 20% of pentaglycyl bridges are not cross-linked and are potential surface-protein attachment sites. None of these sites has a surface protein attached in the planktonic cells, but one-fourth have a surface protein attached in the mature biofilm. Moreover, the leucine-label shows that the concentration of β-strands in leucine-rich regions doubles in the mature biofilm. Thus, a primary event in establishing a S. aureus biofilm is extensive decoration of the cell surface with surface proteins that are linked covalently to the cell wall and promote cell-cell adhesion.

Methicillin-resistant Staphylococcus aureus (MRSA): antibiotic-resistance and the biofilm phenotype

“…Surface proteins known to play important roles in biofilm formation include Bap, clumping factors (ClfB), FnBPs, SasC, SasG, and protein A. ClfB, FnBPs and protein A are widely distributed. [77][78][79][80][81] To target these proteins, and thus disrupt attachment, the Clubb group used an array of small molecules to inhibit MRSA transpeptidase sortase A; MRSA transpeptidase sortase A is a protein that anchors surface proteins to the cell wall. 82,83 In theory, cell surface proteins are a novel therapeutic target to disrupt adhesion or adherence and mitigate biofilm formation.…”

Structural and Functional Dynamics of Staphylococcus aureus Biofilms and Biofilm Matrix Proteins on Different Clinical Materials

“…As structural and functional features of biofilms are greatly dependent on the material and the biofilm growth conditions [38,40,41], there is an obvious demand for comprehensive studies investigating the structural and functional features of the prosthetic materials together with biofilm dynamics on these materials. In this context, the cell surface-associated adhesins have attracted great interest, as many of these can contribute to protein-mediated biofilm formation [39,[42][43][44][45][46]. Recently, an unacknowledged group of surface-associated proteins, i.a., moonlighting virulence factors and cytoplasmic proteins embedded in the staphylococcal biofilm matrix, was proposed to form a new molecular mechanism conferring increased stability for biofilm population [47].…”

Staphylococcus aureus cell wall structure and dynamics during host-pathogen interaction

“…In a S . aureus biofilm, non-crosslinked pentaglycine bridges are used as attachment sites for proteins which are less abundant in planktonic culture [ 61 ]. S .…”

“…These changes occur in the newly synthesised PG rather than a modification to existing PG [11]. In a S. aureus biofilm, non-crosslinked pentaglycine bridges are used as attachment sites for proteins which are less abundant in planktonic culture [61]. S. aureus cells propagate in diverse environments and in the host with each organ provides a different nutrient and immunological repertoire [62], which could result in differing PG structures during an infection.…”