title: Specific binding of aluminium and iron ions to a cation-selective cell wall channel of Microthrix parvicella.
abstract: Heavy metal salts containing aluminium or iron are used in wastewater treatment to control excessive growth of the Gram-positive bacterium Microthrix parvicella, frequently observed in wastewater plants suffering from bulking, foaming and scum. Microthrix parvicella belongs to the class Actinobacteria but not to mycolata, although its taxonomic position in this class is not identified. Investigations using the microspheres adhesion to cells method (MAC) suggested that M. parvicella is as strongly hydrophobic as the mycolic acid containing actinomycetes. The cell wall of M. parvicella was investigated for the presence of water-filled channels using the lipid bilayer assay. An ion-permeable channel called MppA with a conductance of 600 pS in 1 M KCl was identified in cell wall extracts and purified to homogeneity. The cation-selective channel showed no voltage-dependent closure at higher voltages. Interestingly, MPPA could be blocked by heavy metal ions. Binding of polyvalent cations such as iron and aluminium was studied in titration experiments and revealed stability constants for their binding to MppA up to 700 M(-1). The cell wall channel of M. parvicella contains a binding site for polyvalent cations which may play a crucial role for the effect of heavy metals salts on M. parvicella-dominated activated sludge.
authors: Rudolf-Virchow-Center, DFG-Research Center for Experimental Biomedicine, University of Würzburg, Versbacher Str. 9, D-97078, Würzburg, Germany.
authors: Tobias
authors: T
authors: Knaf
authors: Margit
authors: M
authors: Schade
authors: Hilde
authors: H
authors: Lemmer
authors: Roland
authors: R
authors: Benz
mesh_terms: D039903:Actinobacteria / Q000378:metabolism*; D000535:Aluminum / Q000737:chemistry*; D001665:Binding Sites; D002412:Cations / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism*; D007477:Ions / Q000378:metabolism; D007501:Iron / Q000737:chemistry*; D012722:Sewage / Q000382:microbiology*
chemical_list: D002412:Cations; D007473:Ion Channels; D007477:Ions; D012722:Sewage; D000535:Aluminum; D007501:Iron