Francesca Cappitelli

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.

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 K _d 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.

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.