Visualization of Paracoccus denitrificans on various types of stones used in European built heritage

Microorganisms are increasingly recognized for their dual role in the deterioration and conservation of cultural heritage, with Paracoccus denitrificans emerging as a promising candidate for bio-based stone stabilization. This study investigates the biofilm formation of P. denitrificans on stone surfaces, with a focus on five sedimentary rocks -Euville, Savonnières, Bentheimer, Vosges, and Maastricht - selected for their varied porosity, composition, colour and importance for cultural heritage. The samples were inoculated under different nutrient-to-medium ratios to evaluate the impact of inoculation conditions on bacteria-stone interactions. A multi-scale imaging approach using SEM, µ-CT, CLSM, digital microscopy, and colour spectrophotometry provided complementary insights into bacterial distribution, EPS production, biofilm morphology, and mineral deposition. Depending on the stone type, P. denitrificans formed distinct biofilm architectures, including spider web-like networks, spherical aggregates, or uniform surface coatings. Moreover, clear evidence of bacterially induced mineral crystallization was observed. Results reveal that both stone type and medium composition significantly influence biofilm development and mineralization behavior. This integrative methodology demonstrates the potential of P. denitrificans in stone conservation and offers a novel framework for advancing bio-conservation strategies in cultural heritage science.