Biofilms on exposed monumental stones (2009)

Title: Biofilms on exposed monumental stones: mechanism of formation and development of new control methods
Author: Oana Adriana Cuzman
University: University of Bologna (Italy)
Year: 2009
Type of document: PhD thesis
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Abstract

Within the stone monumental artefacts artistic fountains are extremely favorable to formation of biofilms, giving rise to biodegradation processes related with physical-chemical and visual aspect alterations, because of their particular exposure conditions. Microbial diversity of five fountains (two from Spain and three from Italy) was investigated. It was observed an ample similarity between the biodiversity of monumental stones reported in literature and that one found in studied fountains. Mechanical procedures and toxic chemical products are usually employed to remove such phototrophic patinas. Alternative methods based on natural antifouling substances are recently experimented in the marine sector, due to their very low environmental impact and for the bio settlement prevention on partially immersed structures of ships. In the present work groups of antibiofouling agents (ABAs) were selected from literature for their ability to interfere, at molecular level, with the microbial communication system “quorum sensing”, inhibiting the initial phase of biofilm formation. The efficacy of some natural antibiofoulants agents (ABAs) with terrestrial (Capsaicine - CS, Cinnamaldehyde - CI) and marine origin (Zosteric Acid - ZA, poly-Alkyl Pyridinium Salts – pAPS and Ceramium botryocarpum extract - CBE), incorporated into two commercial coatings (Silres BS OH 100 - S and Wacker Silres BS 290 - W) commonly used in stone conservation procedures were evaluated. The formation of phototrophic biofilms in laboratory conditions (on Carrara marble specimens and Sierra Elvira stone) and on two monumental fountains (Tacca’s Fountain 2 - Florence, Italy and Fountain from Patio de la Lindaraja - Alhambra Palace, Granada, Spain) has been investigated in the presence or absence of these natural antifouling agents. The natural antibiofouling agents, at tested concentrations, demonstrated a certain inhibitory effect. The silane-siloxane based silicone coating (W) mixing with ABAs was more suitable with respect to ethyl silicate coating (S) and proved efficacy against biofilm formation only when incompletely cured. The laboratory results indicated a positive action in inhibiting the patina formation, especially for poly-alkyl pyridinium salts, zosteric acid and cinnamaldehyde, while on site tests revealed a good effect for zosteric acid.

Table of contents (compact version):

I. Research Objectives

II. Introduction
II.1. Biofilms formation and evolution
II.2. Biofilms interaction with the substratum, biodeterioration processes
II.3. Biomolecules and biofilm control

III. Materials and Methods
III.1. Investigated fountains
III.2. Biofilms development
III.3. Study of biofilm composition
III.4. Stone material and color measurements
III.5. Antibiofouling agents, coating preparations and their characterization
III.6. Laboratory experiments
III.7. In situ experiments

IV. Results and Discussions
IV.1. Biofilms on monumental stones
IV.2. Antifouling agents as an alternative method for prevention the biofouling on artistic fountains

V. Conclusions
VI. Acknowledgments
VII. Bibliography