Acção da Lisozima sobre bactérias do ácido láctico isolados do vinho

: a influência de proteínas de superfície (S-layer)

Abstract

Lysozyme can be used in wine production to prevent the growth of lactic acid bacteria (LAB) in order to avoid or control the extent of malolactic fermentation (MLF), or to prevent the deterioration caused by these bacteria in post fermentative stages. Previous work demonstrated that the response of wine LAB to lysozyme is species and strain dependent. Some strains of lactobacilli isolated from Port wine were found to be highly resistant to lysozyme (surviving in the presence of 500 to 2000 ppm). It was observed that resistant strains produce a crystalline protein layer (S-layer), which involves the peptidoglycan. It is thought that this layer, consisting exclusively of proteins or glycoproteins, may have a protective role to environmental factors. In this study, we investigated the possible protective role of the S-layer against the action of lysozyme. Various treatments were used to remove this layer from the cells, the treatment with LiCl (5 M) being the most effective, as evidenced by SDS-PAGE. LiCl treated populations of Lactobacillus hilgardii 35 exposed to lysozyme (2000 ppm) were found to keep their resistance in KH2PO4 buffer. However, the substitution of the KH2PO4 buffer by sterile water as celular suspension medium led to an increase in the sensitivity of cells to lysozyme. It was also found that when ethanol (20% v/v) was added to the suspending medium (sterile water), a strong inactivation effect was observed, especially in cells previously treated with LiCl (> 6 log CFU/mL reduction in 30 and 60 min in the presence of 2000 and 500 ppm of lysozyme, respectively). The results show that: a) the S-layer exerts a protective effect against the action of lysozyme; b) the celular suspension medium influences the inactivation efficiency of lysozyme. Components of buffer and wine seem to give osmotic protection to cells which retain their integrity and viability; c) ethanol potentiates the inactivation of cells exposed to lysozyme.

Date of Award	31 Jan 2012
Original language	Portuguese
Awarding Institution	Universidade Católica Portuguesa
Supervisor	José António Couto (Supervisor)