Roberto Marín-Delgado

Microbial colonization is a major cause of deterioration in paintings, leading to discoloration, pigment degradation, and loss of structural integrity. While biodeterioration of artworks has been studied in temperate climates, tropical environments remain underexplored despite their high humidity and temperature, which can promote microbial growth. This study assessed the microbiological deterioration of two 18 ^th -century oil paintings, La Muerte de San José and Virgen de Guadalupe, located in Orosi’s Colonial Church and Religious Art Museum, Costa Rica. Microorganisms were isolated and identified using VITEK 2, microscopy, and matrix-assisted laser desorption ionization–time of flight mass spectrometry analysis, and their biofilm-forming capacity was evaluated. Additionally, the antimicrobial activity of six essential oil components was tested using direct and indirect contact assays. Seventeen bacterial taxa and 15 fungal genera were identified, with Bacillus , Staphylococcus , Cladosporium , and Aspergillus among the most common. Based on the fungal isolate-frequency distributions, Virgen de Guadalupe had a higher Shannon–Wiener diversity index than La Muerte de San José. Several isolates displayed strong biofilm formation, particularly Bacillus subtilis / amyloliquefaciens / vallismortis , and Staphylococcus saprophyticus . Linalool exhibited the strongest inhibitory activity, achieving complete bacterial growth inhibition in non-contact assays. Short-term environmental monitoring documented daily variation in temperature, relative humidity, and CO ₂ concentration during the 8-day measurement period. Together, these results characterize the culturable microorganisms recovered from two tropical heritage paintings and identify volatile essential oil components as candidates for further evaluation in preventive conservation. IMPORTANCE: Understanding the microbiological deterioration of cultural heritage in tropical environments is crucial for designing sustainable conservation strategies. While microbial colonization of artworks has been widely studied in temperate regions, data from tropical heritage settings remain limited. This study integrates microbiological, environmental, and physicochemical analyses to characterize culturable microorganisms recovered from 18 ^th -century oil paintings in Orosi, Costa Rica. By combining microbial identification, biofilm quantification, and essential oil biocide testing, it bridges applied microbiology and cultural heritage conservation. The in vitro inhibition of biofilm-forming bacteria by volatile compounds such as linalool in a non-contact assay supports further investigation of their potential in conservation, including their efficacy and compatibility with artwork materials. These findings provide a basis for future studies of microbial deterioration in tropical heritage settings and for evaluating conservation applications of volatile compounds.

Microbial colonization is a major cause of deterioration in paintings, leading to discoloration, pigment degradation, and loss of structural integrity. While biodeterioration of artworks has been studied in temperate climates, tropical environments remain underexplored despite their high humidity and temperature, which promote microbial growth. This study assessed the microbiological deterioration of two eighteenth-century oil paintings, La Muerte de San Jose and Virgen de Guadalupe, located in Orosi's Colonial Church and Religious Art Museum, Costa Rica. Microorganisms were isolated and identified using VITEK® 2, microscopy, and MALDI-ToF analysis, and their biofilm-forming capacity was evaluated. Additionally, the antimicrobial activity of six essential oil components was tested using direct and indirect contact assays. Twenty-three bacterial species and fifteen fungal genera were identified, with Bacillus, Staphylococcus, Cladosporium, and Aspergillus among the most common. Notably, La Virgen de Guadalupe displayed the highest microbial diversity, reflected in a high Shannon index, indicative of a more complex microbial community. Several isolates displayed strong biofilm formation, particularly Bacillus subtilis/amyloliquefaciens/vallismortis and Staphylococcus saprophyticus. Linalool exhibited the strongest inhibitory activity, achieving complete bacterial growth inhibition in non-contact assays. Environmental monitoring revealed persistently elevated relative humidity and CO2 levels during the study period. Together, these results reveal the complex microbial ecology of tropical heritage paintings and demonstrate that volatile essential oil components can serve as candidates for low-impact antimicrobial strategies in preventive conservation.

We have identified an algebraic error in equation (2), derived from the minimization of the free energy density G with respect to the strain ε . While this error affects the renormalized parameters of the model, it does not alter the subsequent results or conclusions of our publication.

We present a minimal Landau theory of plastic-to-crystal phase transitions in which the key components are a multipole-moment order parameter that describes the orientational ordering of the constituent molecules, coupling between such order parameter and elastic strains, and thermal expansion. We illustrate the theory with the simplest non-trivial model in which the orientational ordering is described by a quadrupole moment, and use such model to calculate barocaloric effects in plastic crystals that are driven by hydrostatic pressure. The model captures characteristic features of plastic-to-crystal phase transitions, namely large changes in volume and entropy at the transition, as well as the linear dependence of the transition temperature with pressure. We identify temperature regions in the barocaloric response associated with the individual plastic and crystal phases, and those involving the phase transition. Our model is in overall agreement with previous experiments in powdered samples of fullerite C₆₀, and predicts peak isothermal entropy changes of ∼ 90 J K − 1 kg − 1 and peak adiabatic temperature changes of ∼ 35 K under 0.60 GPa at 265 K in fullerite single crystals.