Polyethyleneimine-mediated flocculation of Shewanella oneidensis MR-1: Impacts of cell surface appendage and polymer concentration

Marie-Eve Krapf (1) , Bruno Lartiges (2) , Christophe Merlin (2) , Gregory Francius (2) , Jaafar Ghanbaja (3) , Jérôme F.L. Duval (4)

1 LEM - Laboratoire Environnement et Minéralurgie
2 LCPME - Laboratoire de Chimie Physique et Microbiologie pour l'Environnement
3 Laboratoire de Microscopie Electronique
4 LIEC - Laboratoire Interdisciplinaire des Environnements Continentaux

In wastewater treatment plants, optimizing bacterial flocculation and bacterial sludge dewatering requires a detailed understanding of the concommitant biological and physico-chemical processes governing the action of flocculating agent on living cells. Here we investigate the interactions between polyethyleneimine (PEI, 60000 g/mol) and Shewanella oneidensis MR-1 lacking or not the lipopolysaccharide (LPS) O-antigen surface structure. Flocculation tests were performed on bacteria with/without LPS O-antigen after being exposed to 0-100 mg/L PEI concentrations. Measurements of electrophoretic mobility and bacterial aggregates size were complemented by transmission electron micrographs and atomic force microscopy images. While low PEI concentrations (< 20 mg/L) lead to flocculation of both bare and LPS O-antigen-decorated bacterial strains, the lysis of bacterial membranes occurred at larger polymer concentrations for the latter, which highlights the protective role of LPS O-antigen against harmful PEI-mediated membrane alterations. Depending on polymer concentration, two types of bacterial aggregates are identified: one that solely integrates bacterial cells, and another that includes both cells and cell residues resulting from lysis (membrane and/or LPS fragments, and inner cell content materials). The latter is expected to significantly contribute to water entrapping in sludge and thus lower dewatering process efficiency.

Domaines: Ingénierie de l'environnement

Marie-Eve Krapf, Bruno Lartiges, Christophe Merlin, Gregory Francius, Jaafar Ghanbaja, et al.. Polyethyleneimine-mediated flocculation of Shewanella oneidensis MR-1: Impacts of cell surface appendage and polymer concentration. Water Research, 2012, 46 (6), pp.1838-1846. ⟨10.1016/j.watres.2011.12.061⟩. ⟨hal-02187084⟩