Notícias

In Brazil there is a strong effort to study phytophatogenic bacteria and biofilms of citrus plants, since they are a relevant source of income in our economy. In particular, we are interested in the plant pathogen Xylella fastidiosa which grows as a biofilm causing vascular occlusion and consequently nutrient and water stress in different types of plants. We have used Scanning Probe Microscopy (SPM) and fractal analysis on dry biofilms in order to understand basic aspects of the several stages of biofilm development. However, an essential step to biofilm formation is the adhesion of microbial cells to a solid surface. Understanding the factors which determine bacterial adhesion and biofilm development is a key issue in any effort aiming at the identification of mechanisms to prevent biofilm formation. Within these factors, electrostatic interactions between the bacterial cell membrane and a surface have been proposed as an important step for the initial bacterial adhesion. We have thus investigated this process using two different approaches based on SPM capabilities. We have studied surface potential distribution on both abiotic (silicon) and biotic (derivatized cellulose) surfaces by Kelvin Probe Force Microscopy. Furthermore, from a molecular point of view, adhesion forces between these same surfaces and an important membrane adhesin from X. fastidiosa (XadA1) were investigated by force spectroscopy. Our results reveal the interplay between culture medium and substrate as a determinant factor for electrostatic interactions and clearly show the influence of a biopolymer such as cellulose on the surface in determining X. fastidiosa adhesion and biofilm development.