title: Polyethyleneimine-mediated flocculation of Shewanella oneidensis MR-1: impacts of cell surface appendage and polymer concentration.
abstract: In wastewater treatment plants, optimizing bacterial flocculation and bacterial sludge dewatering requires a detailed understanding of the concomitant biological and physico-chemical processes governing the action of flocculating agent on living cells. Here we investigate the interactions between polyethyleneimine (PEI, 60,000g/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 0-100mg/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 (<20mg/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.
authors.affiliation: Laboratoire Environnement et Minéralurgie, Nancy Université, CNRS UMR7569, B.P. 40, F-54501 Vandoeuvre-lès-Nancy, France. marie-eve.krapf@ensg.inpl-nancy.fr
authors.forename: Marie-Eve M
authors.initials: ME
authors.lastname: Krapf
authors.forename: Bruno S
authors.initials: BS
authors.lastname: Lartiges
authors.forename: Christophe
authors.initials: C
authors.lastname: Merlin
authors.forename: Grégory
authors.initials: G
authors.lastname: Francius
authors.forename: Jaafar
authors.initials: J
authors.lastname: Ghanbaja
authors.forename: Jérôme F L
authors.initials: JF
authors.lastname: Duval
mesh_terms: D022081:Cell Surface Extensions / Q000187:drug effects* / Q000378:metabolism; D004553:Electric Conductivity; D004586:Electrophoresis; D005427:Flocculation / Q000187:drug effects; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D008958:Models, Molecular; D019081:O Antigens / Q000378:metabolism / Q000648:ultrastructure; D011094:Polyethyleneimine / Q000494:pharmacology*; D020592:Shewanella / Q000166:cytology* / Q000187:drug effects* / Q000648:ultrastructure
chemical_list: D019081:O Antigens; D011094:Polyethyleneimine