All types of building materials are rapidly colonized by microorganisms, initially through an invisible and then later a visible biofilm that leads to their biodeterioration. Over centuries, this natural phenomenon has been managed using mechanical procedures, oils, or even wax. In modern history, many treatments such as high-pressure cleaners, biocides (mainly isothiazolinones and quaternary ammonium compounds) are commercially available, as well as preventive ones, such as the use of water-repellent coatings in the fabrication process. While all these cleaning techniques offer excellent cost-benefit ratios, their limitations are numerous. Indeed, building materials are often quickly recolonized after application, and microorganisms are increasingly reported as resistant to chemical treatments. Furthermore, many antifouling 5 compounds are ecotoxic, harmful to human health and the environment, and new regulations tend to limit their use and constrain their commercialization. The current state-of-the-art highlights an urgent need to develop innovative antifouling strategies and the widespread use of safe and eco-friendly solutions to biodeterioration. Interestingly, innovative approaches and compounds have recently been identified, including the use of photocatalysts or natural compounds such as essential oils or quorum sensing inhibitors. Most of these solutions developed in laboratory settings appear very promising, although their efficiency and ecotoxicological features remain to be further tested before being widely marketed. This review highlights the complexity of choosing the adequate antifouling compounds when fighting biodeterioration and proposes developing case-to-case innovative strategies to raise this challenge, relying on integrative and multidisciplinary approaches.

Ceramic roof tiles are extremely common building materials that are subjected to the natural phenomenon of biodeterioration, which initially modifies the tile surface and ultimately causes its destruction. The bacterial diversity of the visible biofilm responsible for biodeterioration has been previously examined. In contrast, the early stages of tile colonization and pioneer biofilm growth on these surfaces have been poorly explored. To investigate these pioneering stages of bacterial tile colonization, we combined imagery and conventional culture-based approaches, as well as Illumina-based high-throughput sequencing methods to examine samples collected from unexposed new tiles and tiles that were subjected to few-months outdoor exposure. In all the samples, we observed a pioneering biofilm including a significant bacterial diversity, on both new materials and those subjected to slight exposure, with a total of 279 and 411 different OTUs detected, respectively. This pioneer diversity was dominated by Proteobacteria (more than 50% of the total bacterial diversity) and, at the genus level, by Sphingomonas and the genus 1174-901-12 related to the Beijerinckiaceae. Interestingly, the major patterns of the observed bacterial diversity remained similar between samples collected from unexposed and exposed tiles. Collectively, these data clearly indicate the need to focus on the pioneer colonizing bacteria that form the initial biofilm on building materials, which can subsequently lead to mature biofilm formation and visible biodeterioration.