title: Role of S-layer proteins in the biosorption capacity of lead by Lactobacillus kefir.
abstract: The role of S-layer proteins (SLP) on the Pb(2+) sequestrant capacity by Lactobacillus kefir CIDCA 8348 and JCM 5818 was investigated. Cultures in the stationary phase were treated with proteinase K. A dot blot assay was carried out to assess the removal of SLP. Strains with and without SLP were exposed to 0-0.5 mM Pb(NO3)2. The maximum binding capacity (q max ) and the affinity coefficient (b) were calculated using the Langmuir equation. The structural effect of Pb(2+) on microorganisms with and without SLP was determined using Raman spectroscopy. The bacterial interaction with Pb(2+) led to a broadening in the phosphate bands (1,300-1,200 cm(-1) region) and strong alterations on amide and carboxylate-related bands (νCOO(-) as and νCOO(-) s). Microorganisms without SLP removed higher percentages of Pb(2+) and had higher q max than those bearing SLP. Isolated SLP had much lower q max and also removed lower percentages of Pb(2+) than the corresponding whole microorganisms. The hydrofobicity of both strains dramatically dropped when removing SLP. When bearing SLP, strains do not expose a large amount of charged groups on their surfaces, thus making less efficient the Pb(2+) removal. On the contrary, the extremely low hydrofobicity of microorganisms without SLP (and consequently, their higher capacity to remove Pb(2+)) can be explained on the basis of a greater exposure of charged chemical groups for the interaction with Pb(2+). The viability of bacteria without SLP was not significantly lower than that of bacteria bearing SLP. However, microorganisms without SLP were more prone to the detrimental effect of Pb(2+), thus suggesting that SLP acts as a protective rather than as a sequestrant layer.
authors: Center for Research and Development in Food Cryotechnology, CCT-CONICET La Plata, Calle 47 y 116, 1900, La Plata, Buenos Aires, Argentina.
authors: Esteban
authors: E
authors: Gerbino
authors: Paula
authors: P
authors: Carasi
authors: Cuauhtémoc
authors: C
authors: Araujo-Andrade
authors: E Elizabeth
authors: EE
authors: Tymczyszyn
authors: Andrea
authors: A
authors: Gómez-Zavaglia
mesh_terms: D000327:Adsorption; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001673:Biodegradation, Environmental; D007778:Lactobacillus / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D007854:Lead / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D008562:Membrane Glycoproteins; C055764:S-layer proteins; D007854:Lead
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