Effects of biocide treatments on the biofilm community in Domitilla's catacombs in Rome Clara Urzì a, ⁎, Filomena De Leo a , Lucia Krakova b , Domenico Pangallo b , Laura Bruno c a Department of Chemical, Biological, Pharmaceutical and Environmental Sciences, University of Messina, Viale F. Stagno d'Alcontres 31, 98166 Messina, Italy b Institute of Molecular Biology, Slovak Academy of Sciences, Dubravska cesta 21, 84551 Bratislava, Slovakia c Department of Biology, University of Rome “Tor Vergata”, Via Cracovia 1, 00133 Roma, Italy HIGHLIGHTS • biocide treatments were partially effec- tive against cyanobacteria; • biocide treatments changed the bacteri- al population, increasing their numbers and diversity; and bacteria isolated af- ter the treatment possess high hydro- lytic enzymatic activity; • microbial interaction can have different responses depending on the favourable conditions for one kind of microorgan- ism in respect to the other • bacteria isolated after the treatment could be used as a biocontrol for unde- sirable microbial growth; • need for a different approach for treat- ed bio-deteriorated surfaces of Cultural Heritage. GRAPHICAL ABSTRACT abstract article info Article history: Received 6 May 2016 Received in revised form 27 July 2016 Accepted 27 July 2016 Available online xxxx Editor: D. Barcelo Different types of biofilms are widespread on lithic faces of the Catacombs of Domitilla (Rome, Italy) due to the favorable microclimatic conditions (temperature, high RH% and low irradiance). The biofilm, once established, becomes particularly dangerous due to the coverage of valuable surfaces causing spoilage, softening of materials and mineral precipitation. It is common practice to treat these surfaces with biocides in order to eradicate the mi- croorganisms present. The aim of the present research was to compare the changes occurring to the microbial community present in the biofilm in one site of the Catacombs of Domitilla (CD15) before and after a biocide treatment (a mixture of quaternary ammonium compounds and octylisothiazolone, OIT), applied for a one month period. A multistep approach was followed, based on microscopy, cultural methods and molecular tech- niques (f-ITS and 16S rDNA sequencing), for the phenotypic and genetic analysis of the culturable microbial pop- ulation. Our results highlighted that the biocide treatments had little effect against cyanobacteria, while the bacterial population increased in numbers but changed drastically in terms of diversity. In fact, some bacteria proliferate at the expense of the organic matter released by dead microorganisms as demonstrated by laboratory tests. Further, our data describe how the microbial interaction can have different responses depending on the fa- vorable conditions for one kind of microorganism in respect to the others. This study exemplifies the real risks of applying biocide treatments on complex microbial communities and pin- points the necessity of subjecting treatments to monitoring and reassessment. Moreover, the work showed the Keywords: Stone conservation Microbial communities Biofilm Biocides Microorganisms interaction Science of the Total Environment 572 (2016) 252–262 ⁎ Corresponding author. E-mail addresses: clara.urzi@unime.it (C. Urzì), fdeleo@unime.it (F. De Leo), lucia.krakova@savba.sk (L. Krakova), domenico.pangallo@savba.sk (D. Pangallo), laura.bruno@uniroma2.it (L. Bruno). http://dx.doi.org/10.1016/j.scitotenv.2016.07.195 0048-9697/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv