Role of S-layer proteins in the biosorption capacity of lead by Lactobacillus kefir

GERBINO, O. E.; CARASI, P.; ARAUJO-ANDRADE C.; TYMCZYSZYN E. E.; GOMEZ ZAVAGLIA, A.

WORLD JOURNAL OF MICROBIOLOGY & BIOTECHNOLOGY

SPRINGER

Lugar: Berlin; Año: 2015 vol. 31 p. 583 - 592

0959-3993

The role of S-layer proteins (SLP) on the Pb2+ 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 Pb2+ on microorganisms with and without SLP was determined using Raman spectroscopy. The bacterial interaction with Pb2+ led to a broadening in the phosphate bands (1.300-1.200 cm-1 region) and strong alterations on amide and carboxylate-related bands (COO- as and COO- s). Microorganisms without SLP removed higher percentages of Pb2+ and had higher q max than those bearing SLP. Isolated SLP had much lower q max and also removed lower percentages of Pb2+ 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 Pb2+ removal. On the contrary, the extremely low hydrofobicity of microorganisms without SLP (and consequently, their higher capacity to remove Pb2+) can be explained on the basis of a greater exposure of charged chemical groups for the interaction with Pb2+. 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 Pb2+, thus suggesting that SLP acts as a protective rather than as a sequestrant layer.