The average protein (E+ K)/(Q + H) ratio in organisms has already been demonstrated to have a strong correlation with their optimal growth temperature. Employing the Thermo-Search web tool, we used this ratio as a basis to look for thermostable proteins in a mesophile.. Xylella fastidiosa. Nine proteins were chosen to have their three-dimensional structures modeled by homology, using mainly proteins from mesophiles as templates. Resulting models featured a high number of hydrophobic interactions, a property that has been previously associated with thermostability. These results demonstrate the interesting possibility of using the (E+ K)/(Q + H) ratio to find individual thermostable proteins in mesophilic organisms. (c) 2006 Elsevier Ltd. All rights reserved.