Monitoring the bactericidal effect of UV-A photocatalysis: A first approach through 1D and 2D protein electrophoresis Florence Goulhen-Chollet a,b , Se ´ bastien Josset a,b , Nicolas Keller b , Vale ´ rie Keller b,1 , Marie-Claire Lett a, * a Laboratoire de Ge ´ne ´tique Mole ´culaire, Ge ´nomique, Microbiologie, CNRS, Strasbourg University, 28 rue Goethe, 67083 Strasbourg Cedex, France b Laboratoire des Mate ´riaux, Surfaces et Proce ´de ´s pour la Catalyse (LMSPC), European Laboratory for Catalysis and Surface Sciences (ELCASS), CNRS, Strasbourg University, 25 rue Becquerel, 67087 Strasbourg, France 1. Introduction The report of biocidal effects of TiO 2 in 1985, with the photo- electrochemical killing of microbial cells by semiconductors, opened the door to the use of photocatalysis for the control of pathogenic agents [1]. Photocatalysis has attracted great attention since decades and acts mainly through oxidative photogenerated holes or OH Á radicals [2–4]. The UV-A irradiation of semiconductors leads to the oxidation of the organic constituents of microorgan- isms like for liquid and gas phase organics, and thus inactivates bacteria, viruses, spores, yeasts, etc. [5]. Recent worldwide damage caused by pathogenic microorganisms, gave rise to a stimulating research mainly dealing with self-decontaminating surfaces, or water disinfection and potabilization using TiO 2 suspensions [6–8], mainly targeting bacteria, viruses, fungi, algae and protozoa. Recently, due to major public health problems, the treatment by UV-A photocatalysis of contaminated air received a growing interest inside both industrial and academic communities involved in innovative sustainable environmental research [9–12]. Although the bactericidal effect of photocatalysis is well- documented, notably using TiO 2 suspensions and Escherichia coli bacteria as model target [6–8], the molecular mechanism of the photocatalytic attack over microorganisms is still a blackbox. Studies of the oxidative attack on both the cellular and the molecular levels are necessary not only for fundamental purposes, but also because noticeable differences in sensitivity towards photocatalysis among biomolecules may forecast the development of resistances due to the generalisation of photocatalytic bio- applications, as it has been observed with the overuse of silver in hospitals [13]. Moreover, it can give some clues about the future of the by-products generated during the photocatalytic processes. Viability numerations for evaluating the photocatalytic coating efficiencies towards microorganisms are up to now unsuitable for getting more insight on the necessary molecular understanding of the attack mechanisms. Therefore, although the targets were biological objects and the study of the impact of UV-A photo- catalysis towards such biological targets usually implied biological numeration methods and techniques, replacing a biological approach by a biochemical one was necessary for progressing on the mechanistic knowledge at the molecular level taking place in photocatalysis over microorganisms. To achieve this goal, we focused on the bacterial proteins, since these molecules play important roles in both the structure and the functioning of the cell, and they account for at least 50% of the total cell molecules (except water). Indeed, e.g. for Gram negative bacterial cells such as E. coli and Legionella pneumophila, both inner cytoplasmic and outer membranes (this latter being a part of the cell wall with a peptidoglycan layer) are composed of proteins, phospholipids and various sugars. At the cell surface, these structures act as protective barrier, contributing to maintain vital functions, and constitute the first targets for photocatalysis. This complex layered assembly of high molecular weight compounds Catalysis Today 147 (2009) 169–172 ARTICLE INFO Article history: Available online 15 July 2009 Keywords: 1D and 2D protein electrophoresis UV-A photocatalysis TiO 2 Bacteria Protein degradation Biochemistry ABSTRACT The bactericidal effect of UV-A photocatalysis is studied through the 1D and 2D protein electrophoresis biochemical approach over model and bacterial proteins, which shows that a majority of proteins are heavily and non-specifically damaged. This suggests that the emergence of resistance to this treatment should be almost impossible. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +33 3 90 24 19 97; fax: +33 3 90 24 20 28. E-mail addresses: vkeller@chimie.u-strasbg.fr (V. Keller), lett@unistra.fr (M.-C. Lett). 1 Tel.: +33 3 90 24 27 36; fax: +33 3 90 24 27 61. Contents lists available at ScienceDirect Catalysis Today journal homepage: www.elsevier.com/locate/cattod 0920-5861/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2009.06.001