Application of chemometrics in the analysis of S-layer proteins isolated from lactobacilli strains

P. MOBILI, C. ARAUJO, A. LONDERO, A. GÓMEZ-ZAVAGLIA

São Paulo, Brasil

Congreso; Shedding light on Disease: Optical Diagnosis for the New Millenium; 2008

SPEC

S-layer structures are macromolecular paracrystalline arrays that completely cover the bacterial cell surface1,2. They are attached to the underlying cell wall by non-covalent bonds and usually may be dissociated and solubilized into protein monomers by chaotropic agents such as guanidine hydrochloride and dissociating agents such as 5 M-LiCl1. S-layers have been described in several species of Lactobacillus, such as Lb. acidophilus, Lb. helveticus, Lb. casei, Lb. brevis, Lb. buchneri, Lb. fermentum, Lb. bulgaricus3 and Lb. plantarum3, Lb. kefir and Lb. parakefir4. On the basis that several Lactobacillus species with an S-layer structure play essential roles in many fermentation processes in food industry, silage fermentations, and in probiotics for humans and animals, elucidation of the characteristics of lactobacilli S-layers has become increasingly important5. For this reason, the goal of this work was to structurally characterize S-layer proteins isolated from L. kefir and L. brevis by means of FTIR and Raman spectroscopy. FTIR spectroscopy has been extensively used for the elucidation and analysis of the secondary structure of proteins6-8. On the other hand Raman spectroscopy has been used for microorganism characterization and differentiation9, and characterization of proteins10. In this work, the results obtained by both methodologies have been further used for a chemometric analysis11. Strains of L. kefir and L. brevis have been used for this analysis. They were selected on the basis of their differential surface properties and molecular weights, glycosylation patterns and immunochemical properties of their S-layer proteins. The spectral differences observed in the spectroscopic analysis have been correlated with the structure and composition of the S-layers. The scores plots obtained by PCA and PLS-DA, allowed us to discriminate and classify among lactobacilli species and aggregation grades. Moreover, the loading plots show the spectral regions that contain the information related with the lactobacilli species and aggregation properties. Keywords: FTIR, Raman spectroscopy, Multivariate Analysis.