1 1 Differential effects of biocide treatments on saxicolous communities: 2 case study of the Segovia cathedral cloister (Spain) 3 4 A. de los Ríos*, S. Pérez-Ortega, J. Wierzchos, C. Ascaso 5 Departamento de Biología Ambiental, Museo de Ciencias Naturales-CSIC, Serrano 115 6 dpdo, 28006-Madrid, Spain. 7 8 * Corresponding author. Tel +34 917452500; fax: +34 915640800. E-mail address: 9 arios@ccma.csic.es (A. de los Ríos). 10 11 Keywords: biocides, biodeterioration, biodeteriogens, cyanobacteria, lichens, stone 12 13 ABSTRACT 14 This paper reports the differential elimination of surface lichen thalli and their penetrating 15 hyphae and epilithic and endolithic cyanobacteria by two biocide treatments applied on a 16 small scale to the cloister of the Segovia cathedral. Both chemical treatments were 17 followed by mechanical cleaning and their effects determined by scanning electron 18 microscopy with backscattered electron imaging (SEM-BSE). Both treatments were 19 effective at killing epilithic lichens and cyanobacteria yet showed different effects on 20 endolithic microbiota. The cleaning procedure involving Biotin T dissolved in water 21