Evaluation of materials for Lactococcus lactis immobilization

CLAUDIA BRITOS; ELIANA C DE BENEDETTI; JORGE A. TRELLES; MARIANO GRASSELLI

Tucuman

Congreso; III International Symposium on Lactic Acid Bacteria. II Argentinean LAB Net Meeting International; 2009

Lactococcus lactis is a Gram positive bacteria belonging to Lactic Acid Bacteria group (LAB), which is very broad used in dairy industry for production and preservation of fermented food. Complete genomic information, GRAS status and genetic characteristics are remarkable features for industrial sector to be used as biological factories for recombinant protein, vitamins, antigenic compounds and others. Industrial process using immobilized cells shows many advantages such as easy operability, regio and stereo selectivity and optimized productivity. There are great interests in the selection of materials for cell immobilization, which gives microorganism stability and, at the same time, shows advanced bioprocess features. In this work two different biocatalyst support are analyzed, a synthetic polymer such us macroporous high-density polyethylene (PE) and fibrous cellulose (Cel) as a natural polymer. Both materials, the former one hydrophobic and the second one hydrophilic have low cell-adsorption and biocatalyst stability. In order to improve their cell adhesiveness two different cationic treatment were performed onto materials. Cel was surface modified chemically with a cationazing reagent (Cel-q+) and cationic graft polymerization using polymethacrylates (PE-acryl and Cel-acryl respectively). L. lactis suspensions were adsorbed onto supports for 15 h under stirring. Biocatalyst effectiveness was analyzed by thymidine hydrolysis as a standard chemical reaction. Chemical reaction was followed and quantified by HPLC. Several immobilization steps were done successively in order to evaluate the improvement in biomass loading (up to 5 times) onto polymeric supports. In all cases, an improvement in substrate conversion rate was measured by re-immobilization steps. In average, improvements in initial conversion rate of 80% were detected respect to one immobilization step. Rising up to 90% for the biocatalyst PE-acryl with 3 immobilization steps. Cel-q+ does not show changes in the catalytic activity for re-immobilization steps analyzed (5 times). However, L. lactis immobilized onto Cel-acryl showed improvements higher than 200% in initial conversion rates for two and three re-immobilization steps respect to one immobilization step. Further immobilizations reaches worst results, improving only 60%, probably to cell-agglutination for the excessive microbial loading. Taking into account the absolute product yield, immobilization onto Cel-acryl was the better support with a conversion of 265 ug thymidine/g support/h using 3 immobilization steps. Cellulose fibers modified by graft polymerization with cationic polymethacrylates was the best support to prepare a biocatalyst based on L.lactis.