Adsorption of a Cationic Polyelectrolyte on Escherichia coli Bacteria:  2. Interactions between the Bacterial Surfaces Covered with the Polymer

Abstract

Quaternized polyvinylpyridine (PVPQ) was used as a cationic polymer to destabilize an Escherichia coli bacterial suspension. The optical density and the fraction of free cells, obtained by light scattering measurements, were recorded as a function of the introduced polymer amount, as a way to monitor the stability of the suspension. The flocculation was almost complete for polymer dosages ranging from about 28 to 47 mg of carbon of PVPQ per dry g of bacteria. These dosages correspond to still negatively charged cells, as shown by ζ potential measurements. At low polymer coverages, a less efficient flocculation is observed. At higher dosages, the suspension restabilizes. We interpret these results using our previous study on the adsorption of the polymer chains. We argue that the flocculation at low dosages is rendered possible by the strong inhomogeneities of charge on the bacterial surfaces because of the self-similar configuration of the adsorbed polymer layer and that the restabilization at large dosages is due to the small mesh size of the polymer network on the surface as well as to the Coulombic repulsion between the cells. The properties of the bacterial aggregates were investigated by light scattering. Destabilized suspensions produce aggregates with sizes decreasing as the quantity of adsorbed polymer increases. At the optimum of flocculation, the polydispersity of the aggregates is low, suggesting a diffusion-limited aggregation mechanism (DLA). The presence of the characteristic self-similar structure of DLA aggregates, with a fractal dimension on the order of 1.9, is suggested by some of the light diffusion experiments. On the other hand, at low coverages, that is, when only some regions on the surfaces are covered with polymers, the flocculation seems to obey a reaction-limited aggregation, with a large polydispersity in the size of the aggregates.

Biocompatible nanoparticles trigger rapid bacteria clustering

“…The dilute (OD 600 $ 0.1) clusters contain a smaller proportion of bacteria, and some bacteria are free or in small aggregates. The moderately sized clusters formed under such conditions, with a large excess of nanoparticles, suggest the presence of mild deflocculation of the bacteria, similar to observations of colloid restabilization at high polymer concentration in previous studies of molecular chitosan, 5,14,15 and molecular polyvinylpyridine 33 as aggregation agents. Further experiments performed at even higher chitosan nanoparticle concentrations will indicate whether the nanoparticle concentration behavior diverges from classical flocculation theory, 33 or whether the concentration range examined here is too limited for significant deflocculation to occur.…”

“…For example, Châtellier et al were the first to study the impact of a cationic polymer, polyvinylpyridine, on the stability of an E. coli suspension, and found that the bacteria flocculation is highly dependent on the polymer concentration. 33 Pearson et al found that a characteristic zeta potential can be used as a measure of optimal flocculation of different fermentation broth systems, and is independent of the added polymer dose, concentration, and dosing method. 34 An interesting question that this study begins to address is how well the predictions of classical flocculation theory describe the behavior of nanoparticle flocculants.…”

Effect of Growth Phase and Metabolic Activity on the Adhesion ofEscherichia coliK-12 AB264 to Quartz and Lepidocrocite

“…However, it should be remembered that bacterial adhesion is not always only driven by first-order electrostatic interactions. The architecture of charge heterogeneities on the bacterial surfaces can be significant, and it can lead to attractive interactions even between negatively charged surfaces (e.g., Châtellier et al 2001;Walker et al 2005).…”

Deciphering the aggregation mechanism of bacteria (Shewanella oneidensis MR1) in the presence of polyethyleneimine: Effects of the exopolymeric superstructure and polymer molecular weight

“…The aggregation of bacteria with polyelectrolytes is a crucial stage in many water treatment operations and biotechnological processes [1][2][3][4]. The intrinsic complexity of the microorganisms, their diversity, their intricate biointerphasial features (presence/absence and nature of their extracellular polymeric substances), make it difficult to assess the interaction mechanisms between the polyelectrolyte and the biocolloids.…”