Associative and Entanglement Contributions to the Solution Rheology of a Bacterial Polysaccharide

Abstract

We report the viscosity of semidilute solutions of a bacterially synthesized polysaccharidea partially deacetylated poly-N-acetylglucosamineas measured by microrheology. This polymer, commonly called polysaccharide intercellular adhesin (PIA), is synthesized by Staphylococcal strains; it is a principal component of the biofilms of these bacteria. We show that the concentration-dependent viscosity of PIA at a pH in which it is associated can be predicted using the Heo–Larson equation for entangled polymers [J. Rheol.20054911171128], if the molecular parameters of the equation are measured in its associated state. This agreement is consistent with PIA adopting a concentration-dependent scaling of the viscosity that is dominated by entanglements and intermolecular associations, as described in the theory of Rubinstein and Semenov [Macromolecules20013410581068]. The zero-shear specific viscosity, ηsp, measured in the concentration range, c PIA = 0.1–13 wt %, scales as ηsp ∼ c PIA 1.27±0.15 up to an entanglement concentration, c e = 3.2 wt %, after which ηsp ∼ c PIA 4.25±0.30. In the presence of urea, a known disruptor of associations, these scaling shifts to ηsp ∼ c PIA 1.02±0.2 and ηsp ∼ c PIA 2.57±0.6, respectively; no shift in c e is observed. The urea effect is consistent with an associative contribution to viscosity in the aqueous solution case. The invariance of c e suggests that the rheology of this polymer–solvent system also includes an entanglement contribution. With independent estimates of the PIA weight-average molar mass, M w, entanglement molecular weight, M e, hydrodynamic radius, R H, and excluded volume, ν, we use the Heo–Larson equation to predict ηsp as a function of c PIA. With the use of parameters from the associated stateparticularly the hydrodynamic radiuswe find good agreement between the model and data for aqueous PIA solutions. This study offers a means to predict the rheology of associating polysaccharides using correlations for nonassociating polymers adjusted with minimal a priori data from their associated state.

Shear rheology and scaling of semiflexible polymers: Effect of polymer‐solvent interactions in the semidilute regime

“…After normalizing for the Rouse viscosity, they determined the relationship η p / η Rouse ∝ c 2.95 . This theory was confirmed by Ganesan et al 73 where the viscosity of bacterial polysaccharide solutions in the nonassociated state scaled as η o ∝ c 1 for c < c* , and η o ∝ c 2.57 for c > c* . Recent simulation studies evidenced the significant influence of chain flexibility on shear viscosity, and how chain stiffness can tune the shear viscosity 75 …”

“…Note that the reputation theory predicted m = 3 for flexible polymers although experimental evidence showed that the scaling is m = 3.4 22 . Hence, experimental evidence suggests that the molecular conformation plays a critical role in the polymer's dynamics and this would be one of the driving factors for the scaling of the zero‐shear rate viscosity η o 25–44,54,56,73 . Table 1 summarizes the exponents n and m determined for the scaling of η o with concentration and molecular weight for a range of rigid‐chain polymers.…”

Bacterial Biofilm Material Properties Enable Removal and Transfer by Capillary Peeling

“…However, our measurements show that the unstructured VPS does not increase the biofilm storage modulus, because the hydrogen-bond based interactions between individual polysaccharide chains are similar to those between individual LPS units. [25] To strengthen the biofilm, two strategies are employed. First, the polymer network is reinforced by cross-linking via RbmC/Bap1 (Figure 1c, blue).…”

Surviving as a Community: Antibiotic Tolerance and Persistence in Bacterial Biofilms

“…The main S. epidermidis matrix component is called polysaccharide intercellular adhesin (PIA), a positively charged polymer (Otto, 2009). At low pH, purified PIA in solution possesses concentration-dependent viscoelasticity that is well described by the classical model of associative polymers: polymers that can both physically entangle and chemically interact through hydrogen bonding (Ganesan et al, 2016). The main contribution to biofilm rheology, however, stems from chemical interactions, as the concentration of PIA in biofilms is too low for physical entanglement.…”