The bacterial community of membrane biofilms of an individual full-scale reverse osmosis (RO) plant, operational with brackish water, was analyzed using a combination of culture-dependent and molecular-based techniques. Samples were collected a few hours after the RO membrane was removed from operation. Visualization of the RO membrane exhibited the presence of a slimy, opaque, dark-brown deposit on the surface of all membrane sheets and feed spacers, indicating that the fouling layers were not eliminated by the routine cleaning procedures of the RO unit operation. Results indicated that most of species identified were affiliated with the gamma-Proteobacteria subdivision mainly comprising of Pseudomonas and Xanthomonas followed by Sphingomonas affiliated to alpha-Proteobacteria and finally by beta-Proteobacteria using both the techniques. (C) 2010 Elsevier B.V. All rights reserved.