Microbial adhesion to solvents: A novel method to determine the electron-donor/electron-acceptor or Lewis acid-base properties of microbial cells

Lewis acid-base, i.e. electron-donor/electron-acceptor, interactions are implicated in various interfacial phenomena such as phagocytosis, biofouling and microbial adhesion. Therefore, the determination of electron-donor/electron-acceptor properties of microbial cells can be of importance in many research areas. However, until now, there has only been one method to determine these properties which is based on contact angle measurements combined with the equations of van Oss. Consequently, this method requires specific and elaborate equipment. Thus to facilitate the characterization of microbial cell surfaces, we have developed a simple, rapid and quantitative technique, the MATS (microbial adhesion to solvents) method, which is based on the comparison between microbial cell affinity to a monopolar solvent and a polar solvent. The monopolar solvent can be acidic (electron acceptor) or basic (electron donor) but both solvents must have similar surface tension Lifshitz-van der Waals components. Using this new method we have shown that Streptococcus thermophilus B (STB) and Leuconostoc mesenteroides NCDO 523 (LM 523) display maximal affinity for an acidic solvent and a low affinity for basic solvents. There was not a great difference between microbial cell adherence to basic solvents and apolar solvents, except for STB suspended in a 0.1 mol l(-1) potassium phosphate buffer. These results, which demonstrate that both bacteria are strong electron donors and very weak electron accepters, are in accordance with the energetic characteristics derived from van Oss's approach.