Water plays a key role in the durability of building materials, including stone-built heritage. A primary contributor to the weathering mechanisms affecting stone materials exposed outdoors, water is also essential to regulate colonization by subaerial biofilms (SABs). Recent studies have suggested that SABs influence water transport properties of biocolonized porous substrates, potentially offering protective effects by reducing surface wettability and slowing capillary water absorption. However, their impact on moisture sorption, drying rate, and water vapor permeability remains unclear. To systematically investigate how SABs influence water and moisture transport in porous stone materials, reproducible, well-characterized laboratory models are essential. Current methods often result in uneven SAB formation and distribution, limiting the reliability of experimental results. Therefore, an existing protocol was optimized to ensure complete and homogeneous SAB coverage. Such optimized stone-SAB models allow for quantitative measurements of capillary absorption, drying rate, hygroscopic sorption, and water vapor permeability with greater precision and reliability than previously achievable. Subsequently, the effects of laboratory-grown mono-species and dual-species SABs on such properties were evaluated. The results confirm the potential of SABs in reducing capillary absorption and provide new insights into moisture dynamics in the SAB-stone system, a key aspect that remains poorly understood. Overall, this study advances the understanding SAB–substrate interactions and aims to contribute to a shift in perspective regarding biocolonization in built environment conservation.

Stone surfaces are colonized by subaerial biofilms (SABs), complex multicellular communities embedded in a self-produced matrix of hydrated extracellular polymeric substances (EPS). Recent studies have shown that the SABs on artistic surfaces are not only detrimental, leading to biodeterioration, but they can also have a protective role. This is especially true for porous stones, where the SABs form a protective interface layer between the lithic material and the surrounding environment. This study reproduced mono and dual-species SABs on limestone coupons to examine stone surface properties with both living and dead SABs under moist (75

Stone heritage is central to cultural identity, yet alpine monuments remain understudied and vulnerable to deterioration. In mountain environments, moisture and temperature fluctuations promote salt crystallisation in porous geomaterials, frequently associated with rosy discolouration attributed to pink biofilms, a phenomenon still poorly explored at higher elevations. Here, we investigated rosy discolouration at about 1000 m altitude on the walls of St. Cyprian Chapel (South Tyrol) using metabarcoding and chemical analyses. We compared two cases of rosy discolouration: one on the north wall, where salt efflorescence is present, and one on the south wall, where it is absent. The aim was to characterise how salt efflorescence modulates rosy discolouration by comparing the two walls and linking substrate chemistry and mineralogy to biofilm pigments, structure, and microbial community composition. Despite similar mineralogy, the north wall exhibited distinct surface chemistry consistent with salt efflorescence. Biofilm biomass was comparable between walls, and no photosynthetic organisms were detected in either biofilm, yet microbial communities differed markedly. The south wall hosted carotenoid-producing biomarkers, including Rubrobacter and Pontibacter, although Raman did not detect carotenoid signals, indicating low pigment expression. In contrast, the north wall showed stronger discolouration and clear detection of bacterioruberin. Notably, the north-wall biomarker Chryseobacterium may also contribute to the rosy discolouration through flexirubin-type pigments. Overall, salt efflorescence is not required for pink biofilm establishment, but salt-rich microhabitats appear to enhance pigment production. This study provides new insights into the drivers of rosy discolouration and contributes to the still-limited research on alpine cultural heritage.

Biomineralization results directly from microbial metabolic processes creating the conditions for inorganic minerals to deposit within and around cells. Across diverse habitats, many cyanobacterial species, biofilms or planktonic, promote extracellular calcium carbonate (CaCO3) precipitation or intracellular CaCO3 deposits. Although biomineralization occurs across all domains of life, cyanobacteria display an exceptional capacity for this process. Cyanobacterial mineralization is largely a byproduct of photosynthetisis, supported by carbonic anhydrases (CAs), the carbon-concentrating mechanism (CCM), and the production of extracellular polymeric substances (EPS). Environmental factors including pH, ion concentration, nutrient levels, temperature, salinity, and hydrodynamic conditions influence the occurrence and rate of mineral precipitation and its composition and morphology. Through these mineralizing activities, cyanobacteria modify sediment properties, contribute to global carbon cycling, and generate extensive geological formations. Simultaneously, the formation of mineralized structures, often associated with organic matrices, enhances cyanobacterial survival by providing mechanical protection, improving metabolic efficiency, and increasing ecological competitiveness. In this review, we present an integrated perspective on the biological, metabolic, molecular, and environmental foundations of cyanobacterial biomineralization. Highlighting the mechanisms connecting EPS synthesis, biofilm dynamics and photosynthesis to mineral formation in natural and artificial environments. Compared with other microbial systems, cyanobacterial biomineralization offers a sustainable safe option for promising applications, particularly bioconsolidation for cultural heritage conservation. Their controllable growth, adaptability to diverse substrates and challenging environments, and ability to form cohesive mineral-organic matrices make them especially suitable for novel and impactful applications such as the bioconsolidation of weathered stone heritage and the production of geomaterial under microgravity.

Unwanted graffiti made by spray paints are one of the most severe environmental pollutants that affect historical and modern buildings. Microorganisms offer a powerful, safe, eco-friendly, sustainable and low-cost biobased solution to remove graffiti from urban surfaces compared to conventional chemical and physical methods. However, a fully satisfying biocleaning procedure for the removal of spray paint has not yet been achieved due to the complexity of the paint composition, together with the fact that most of microorganisms found on paint films are airborne contaminants rather than active degraders. Spray paints contain xenobiotic compounds, creating an extreme environment for most microbial life. In this research a lab-scale biofilm enrichment strategy was developed to retrieve bacteria suitable for biocleaning purposes from spray paint in cans. Results indicated that this selective strategy i) effectively enriched non-endospore-forming bacteria suited to survive the harsh physicochemical conditions of canned paint; ii) established stable subaerial biofilms on painted surfaces, as demonstrated by metagenomic analysis using Illumina next generation sequencing technology; iii) utilised paint components as the sole carbon and energy source; and iv) remained amenable to large-scale, low-cost production for potential biocleaning applications. The most abundant taxon in both black and silver paints was isolated, sequenced using standard methods and identified as Klebsiella aerogenes.

Subaerial biofilms (SABs) are microbial communities that form on surfaces exposed to both air and periodic moisture and that can adapt to harsh environmental conditions like UV radiation, and fluctuating temperatures. On the one hand they can protect built surfaces by forming a barrier against environmental stressors, on the other they can also cause deterioration through biological weathering. The balance is complex and depend on a large number of factors. Unfortunately, only a small part of the complex multiscale network of physical, chemical and biological processes is captured by existing mechanistic model; this prompts for the involvement of phenomenological models. In this work we point at the modeling advantages offered by Bayesian Networks (BNs), Causal Networks and Targeted Learning (TL) in the study of the dual role of SABs.

Zosteric acid (ZA), or p-(sulphooxy)-cinnamic acid, is a secondary metabolite of the seagrass Zostera marina able to reduce biofilm formation of a wide range of bacteria and fungi, through a nonbiocidal mode of action. However, the lack of information concerning the specific chemical structural elements responsible for ZA's antibiofilm activity has hindered the scaling up of this green-based technology for real applications. In this study, a small library of molecules based on ZA scaffold diversity was screened against the eukaryotic fungus Candida albicans, in order to identify the key chemical features of ZA necessary for inhibiting fungal biofilm at sublethal concentrations. Results, supported by multivariate statistical analysis, revealed that the presence of (i) the trans (E) double bond, (ii) the free carboxylic group in the side chain, and (iii) the para substitution with a hydroxyl group were all instrumental for maintaining the antibiofilm activity of the molecules. Additionally, molecular modeling studies suggested that the best performing derivatives interacted with NADP-(H) quinone oxidoreductase, influencing the microbial redox balance.

The study of the historical built environment is of great significance to the heritage conservation and the reconstruction of the level of anthropogenic pollution in the past. On the Dazu Rock Carvings, China, a black to reddish-brown, relatively dense mineral film with a thickness of approximately 150 mu m was observed on the surface of the sandstone. The chemical composition of the mineral film studied by Scanning Electron Microscopy- Energy Dispersive Spectroscopy (SEM-EDS), Electron Probe Micro- Analyz (EPMA), X-ray Absorption Spectroscopy (XAS), Total Organic Carbon (TOC), and Ion Chromatography (IC), revealed that its development was comprehensively controlled by environmental conditions, especially by environmental pollution. The mineral film consisted primarily of clay minerals and iron oxide. It also contained a large amount of detrital quartz and feldspar, with a clear boundary with the underlying mineral matrix. The bacterial community was also investigated by next generation sequencing and its potential metabolisms through PICRUSt2. The mineral film on the surface of sandstone and its microbial community may provide a certain degree of protection for the internal structure. As a passive sampler, the variation of the concentration of pollution elements in the mineral film is helpful to understand the past environmental pollution of the city. Besides the relevance for stone heritage conservation, this study provides insights into the interplay between geological materials and the environment. (c) 2025 Elsevier Masson SAS. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Biofilms pose significant challenges in multiple settings due to their resistance to conventional treatments. In this study, we designed and synthesized a novel class of nature-inspired 5,7-dihydroxy-2,2-dimethylchroman-4-one derivatives as binders of WrbA, a potential target for biofilm modulation. Using a structure-based computational approach, a small library of analogs with varied amide moieties was developed and synthesized. The evaluation of their binding affinity to WrbA demonstrated good-to-excellent Kd values, as confirmed by microscale thermophoresis (MST). Antibiofilm assays against Escherichia coli and Staphylococcus aureus revealed different modulating effects on biofilm formation, conceivably linked to ROS production. These findings emphasize the importance of ROS levels in biofilm, as well as the pivotal role of WrbA as a target in its regulation.

Previous studies mainly focused on the impact of climatic conditions on stone heritage microbial communities, while ignoring a global ecological perspective of pollution on heritage microorganisms. In particular, there is a lack of detailed analysis of the impact of pollution levels on microbial metabolic function. In this study, >6000 bacterial OTUs from 17 world cultural heritage sites were considered. The microbial diversity indexes and potential functions under different pollution levels were analyzed. The results show that particulate matter pollution, such as PM2.5, has an effect on the microbial community in heritage sites comparable to that of temperature and precipitation. High concentrations of particulate matter increased bacterial richness and facilitated the introduction of unique species. Among them, phototrophic bacteria (e.g., Cyanobacteria) and some heterotrophic bacteria (e.g., Actinobacteria and Proteobacteria) formed the core of the microbial community. However, high concentrations of particulate matter reduced the complexity and stability of microbial ecological networks, favoring pollution-tolerant species. Furthermore, elevated particulate concentrations partially suppressed the expression of certain metabolic pathways, particularly genes related to denitrification (e.g., nosZ and nirS). This study reveals the long-term impact of polluted environments on the diversity and potential functions of microbial communities, providing a theoretical basis for developing sustainable strategies for cultural heritage conservation.

While traditionally confined to laboratory settings, recent developments have enabled Water Contact Angle (WCA) measurements to be conducted on-site, under field conditions. This study presents a comparative evaluation of a conventional benchtop method and a portable instrument applied to uncolonized and biocolonized stone surfaces. A reference non-absorbing substrate was used for method validation. Results showed good agreement between the two methods on non-absorbing surfaces, confirming the reliability of the portable approach. On porous biocolonized substrates, the methods differed in absolute WCA values but showed consistent trends, while there was good agreement among drop absorption times. These findings demonstrated that the portable approach can effectively capture water-related properties on-site, with minimal invasiveness and high reproducibility. The study introduces a validated and statistically supported methodology for on-site wettability and water absorption assessment and emphasizes the influence of biofilm composition on surface water-related properties, contributing to the broader understanding of SAB-induced surface modification.

AbstractThis paper provides insights into the paper submission and review processes and the possible reasons behind paper acceptance or rejection. The main target of this paper is emerging researchers who are writing their first scientific papers in peer-reviewed journals. This manuscript gives clues on how to select a journal and what a preprint is, introduces authorship and the roles of editors, reviewers, and publishers, sheds light on the editorial process, and briefly introduces some ethical issues arising in scholarly publishing. The content is based on a course offered annually to doctoral students at the University of Milan and keeps into account frequently asked questions. The authors of this paper are an editor-in-chief and an associated editor of scientific journals, respectively.

The 17th Century Casa a Ponente of Palazzo Rocca Costaguta’s wall provided an opportunity for an evaluation based on a Life Cycle Assessment (LCA) approach of conservation treatments aiming at removing biological colonization from built heritage surfaces. The investigated surfaces were historic plasters partially covered by a patchy green patina due to biofilm recolonization soon after a previous biocidal treatment. Areas of the biocolonized wall were treated by conservation professionals according to both conventional and “green” (i.e., exploiting natural active principles) biocidal products, including Preventol RI 50 (active substance benzalkonium chloride), Essenzio (active substance essential oregano oil), and hydrogen peroxide. Upon treatment, LCA analysis was conducted to evaluate the environmental impact of the different solutions, including a no-treatment option. LCA analysis was based on on-site investigations of the untreated wall surface with and without biofilm and following the biocidal treatment. The conservation treatment’s impact on the mineral substrate was based on digital microscopy, colorimetry, and water contact angle measurements via an innovative portable method. The results highlighted the impacts of the different biocidal treatments, which, in some cases, have not completely removed the biofilm and, in some cases, have altered the surface properties of the plaster. This pointed out the opportunity to re-think conservation strategy, including LCA analysis as a complementary tool to assess the environmental impact of the different conservation treatments and procedures.

Biofilm deterioration and biofilm protection should be considered as different aspects of the complex interactions between microbes and the surfaces of outdoor heritage (e.g. stones, bricks, mortar and plaster). Thus, it is urgent to verify and quantify to what extent the biofilm can protect from different weathering processes, to eventually determine the advisability of biofilm removal from the heritage surfaces. On one hand, it is necessary to more precisely describe the decaying processes caused by the microorganisms and to quantify the extent, severity, and rate at which the microorganisms are causing the decay. On the other hand, it is necessary to define methodologies to comprehensively study the bioprotection phenomena. So far, no decision-making tool is available to guide heritage professionals in deciding whether to remove or keep biofilms on heritage surfaces, and aesthetical alteration and discoloration is often the only criterion considered. In this work the different available approaches for the study of the dual role of biofilms on outdoor heritage have been critically reviewed. The open challenges and questions are also summarised.

Biofilms colonize both biotic and abiotic surfaces, including living tissues, medical devices, water supply systems, and food processing equipment, posing health risks and financial burdens. In the present study, inorganic nanoparticles were functionalized with p-aminosalicylic acid or p-aminocinnamic acid, both established antibiofilm agents at non-lethal concentrations. The final aim was to obtain new nanosystems for surface covering, mitigating the drawbacks associated with current antifouling coatings and tackling the pressing issue of antimicrobial resistance. Two series of silica nanoparticles were synthesized and characterized; the one with the highest degree of functionalization was selected for coating glass coverslips. The anti-biofilm properties of the resulting surfaces were tested against Pseudomonas aeruginosa biofilm. All coated surfaces showed a significant reduction in biofilm formation compared to the untreated controls, with a decrease ranging from -59.2 +/- 2.2 to -83.7 +/- 3.4. Importantly, the anti-biofilm coating did not affect the bacterial viability of both planktonic and sessile cells. Interestingly, the interaction between bacteria and the new surfaces led to an increase in bacterial metabolic activity, total protein amount, and oxidative stress levels. These findings indicate that the coatings affect biofilm formation by influencing bacterial physiology rather than simply killing the bacteria outright.

Rock art paintings represent fragile ecosystems supporting complex microbial communities tuned to the lithic substrate and climatic conditions. The composition and activity of these microbial communities associated with different weathering patterns affecting rock art sites remain unexplored. This study aimed to explore how bacterial communities adapt their ecological strategies based on substrate weathering, while also examining the role of their metabolic pathways in either biodeterioration or bioprotection of the underlying stone. SEM-EDS investigations coupled with 16S rRNA gene sequencing and PICRUSt2 analysis were applied on different weathered surfaces that affect southern Ethiopian rock paintings to investigate the relationships between the current stone microbiome and weathering patterns. The findings revealed that samples experiencing low and high weathering reached a climax stage characterized by stable microenvironments and limited resources. This condition favored K-strategist microorganisms, leading to reduced α-biodiversity and a community with a positive or neutral impact on the substrate. In contrast, moderately-weathered samples displayed diverse microhabitats, resulting in the prevalence of r-strategist bacteria, increased α-biodiversity, and the presence of specialist microorganisms. Moreover, the bacterial communities in moderately-weathered samples demonstrated the highest potential for carbon fixation, stress responses, and complete nitrogen and sulfur cycles. This bacterial community also showed the potential to negatively impact the underlying substrate. This research provided valuable insights into the little-understood ecology of bacterial communities inhabiting deteriorated surfaces, shedding light on the potential role of these microorganisms in the sustainable conservation of rock art.

Understanding the impact of sessile communities on underlying materials is of paramount importance in stone conservation. Up until now, the critical role of subaerial biofilms (SABs) whether they are protective or deteriorative remains unclear, especially under desiccation. The interest in desiccated SABs is raised by the prediction of an increase in drought events in the next decades that will affect the Mediterranean regions' rich stone heritage as never before. Thus, the main goal of this research is to study the effects of desiccation on both the biofilms' eco-physiology and its impacts on the lithic substrate. To this end, we used a dual-species model system composed of a phototroph and a chemotroph to simulate biofilm behavior on stone heritage. We found that drought altered the phototroph-chemotroph balance and enriched the biofilm matrix with proteins and DNA. Desiccated SABs underwent a shift in metabolism to fermentation and a decrease in oxidative stress. Additionally, desiccated SABs changed the water-related dynamics (adsorption, evaporation, and wetting properties) in limestone. Water absorption experiments showed that desiccated SABs protected the stone from rapid water uptake, while a thermographic survey indicated a delay in water evaporation. Spilling-drop tests revealed a change in the wettability of the stone-SAB interface, which affected the water transport properties of the stone. Finally, desiccated SABs reduced stone swelling in the presence of water vapor. The biodeteriorative and bioprotective implications of desiccated SABs on the stone were ultimately assessed.

Bacterial biofilm is a major contributor to the persistence of infection and the limited efficacy of antibiotics. Antibiofilm molecules that interfere with the biofilm lifestyle offer a valuable tool in fighting bacterial pathogens. Ellagic acid (EA) is a natural polyphenol that has shown attractive antibiofilm properties. However, its precise antibiofilm mode of action remains unknown. Experimental evidence links the NADH:quinone oxidoreductase enzyme WrbA to biofilm formation, stress response, and pathogen virulence. Moreover, WrbA has demonstrated interactions with antibiofilm molecules, suggesting its role in redox and biofilm modulation. This work aims to provide mechanistic insights into the antibiofilm mode of action of EA utilizing computational studies, biophysical measurements, enzyme inhibition studies on WrbA, and biofilm and reactive oxygen species assays exploiting a WrbA-deprived mutant strain of Escherichia coli. Our research efforts led us to propose that the antibiofilm mode of action of EA stems from its ability to perturb the bacterial redox homeostasis driven by WrbA. These findings shed new light on the antibiofilm properties of EA and could lead to the development of more effective treatments for biofilm-related infections.