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.

Rift Valley fever virus (RVFV) is a highly pathogenic zoonotic arbovirus endemic in many African countries and the Arabian Peninsula. Animal infections cause high rates of mortality and abortion among sheep, goats and cattle. In humans, an estimated 1-2% of RVFV infections result in severe disease (encephalitis, hepatitis, retinitis) with a high rate of lethality when associated to hemorrhagic fever. RVFV's NSs protein, which is RVFV's main factor of virulence, counteracts the host innate antiviral response favoring viral replication and spread. However, the mechanisms underlying RVFV-induced cytopathic effects and the role of NSs in these alterations remain for the most undeciphered. In this work we have analyzed the effects of NSs expression on actin cytoskeleton while conducting infections with the NSs expressing virulent (ZH548) and attenuated (MP12) strains of RVFV and the non-NSs expressing avirulent (ZH548ΔNSs) strain as well as after the ectopic expression of NSs. In macrophages, fibroblasts and hepatocytes NSs expression prevented the up-regulation of Abl2 (a major regulator of actin cytoskeleton) expression otherwise induced by avirulent infections and identified here as part of the antiviral response. The presence of NSs was also linked to and increased mobility of ZH548- as compared to ZH548ΔNSs-infected fibroblasts and to strong changes in cell morphology in non-migrating hepatocytes with reduction of lamellipodia, cell spreading and dissolution of adherens junctions reminiscent of ZH548-induced cytopathic effects observed in vivo. Finally, we show evidence of the presence of NSs within long actin-rich structures associated to NSs dissemination from NSs expressing towards non-NSs expressing cells. Importance. Rift Valley fever virus (RVFV) is a dangerous human and animal pathogen that was ranked in 2018 by the World Health Organization among the eight pathogens of most concern likely to cause wide epidemics in the near future for which there is no, or insufficient, countermeasures. The interest of this work resides in the fact that it addresses the question of the mechanisms underlying RVFV-induced cytopathic effects that participate in RVFV's pathogenicity. We demonstrate here that RVFV targets cell adhesion and actin cytoskeleton at the transcriptional and cellular level, affecting cell mobility and inducing cell shape collapse alongside with distortion of cell-cell adhesion. All these effects are susceptible to participate in RVFV-induced pathogenicity, facilitate virulent RVFV dissemination and thus constitute interesting potential targets in future development of antiviral therapeutic strategies that in the case of RVFV, as several other emerging arboviruses, are presently lacking.

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Ceramic roof tiles are widespread marketed building materials, rapidly colonized by microorganisms that form multispecies biofilms on their surface and play crucial roles in biodeterioration processes. Coating tiles with water repellents is a pervasive industrial strategy employed to prevent liquid water penetration and slow biodeterioration. Very few studies have examined the links between the characteristics of water-repellent coatings and biofilm colonization patterns. Our work aims to compare the effects of coating tiles with two common water repellents (siliconate and siloxane) on the growth of colonizing microbes. We combined in situ exposure of tiles for over six years and macroscopic and microscopic observations with in vitro biotests, relying on the use of algal and fungal models. Our data showed that (1) tiles coated with water repellents were macroscopically less colonized by lichens (2) a significant fungal biofilm development at the microscopic scale (3) water repellents had very contrasting effects on our model strains. These data reinforce the great interest for industry to conduct more studies linking the nature of the water repellents with the composition of colonizing multispecies biofilms. The long-term objective is to improve the available water repellents and better adapt their selection to the nature of microbial colonization.