Essential oils and extracts of plants as biocides against microorganisms isolated from the ruins of the Roman city of Conímbriga (Portugal)

Biodeterioration of monumental complexes is in large part due to the proliferation of various microorganisms that attack the physical-chemical structures of support materials. Various conservation and restoration interventions use commercial biocides of synthetic origin, which exhibit some human and environmental toxicity and sometimes side effects on support materials. The main objective of this work is the assessment of new biocides obtained from endemic Mediterranean plants, to be used in the preservation of cultural heritage with the goal of contributing to the sustainable use of ecosystems and to the development of Mediterranean local communities. The biocidal potential of essential oils (EOs) and solvent extracts (SEs) (ethanol and n-hexane) obtained from four plants were evaluated: Thymus mastichina (Tm), Mentha pulegium (Mp), Foeniculum vulgare (Fv), and Lavandula viridis (Lv). Microorganisms collected at an emblematic site of Portuguese cultural heritage, the ruins of the Roman city of Conímbriga, were used to evaluate the biocidal activity of the EOs and SEs. It can be concluded that (i) SEs did not exhibit fungicidal nor bactericidal activity, except for one fungus specie; (ii) biocidal activity of EOs depends on the microorganism specie. The EOs showed a relative average biocidal activity (when compared to the commercial biocide Biotin T (1% v/v)) of 64%, 32%, 30%, and 25% for Mp, Fv, Lv, and Tm. On carbonate rocks, the application of Fv and Mp EOs up to 3 layers do not promote significant color/tonality changes in the surface of the rock. And the application of three layers of Lv and four layers of Fv, Mp, and Lv OEs only promote the occurrence of blurs or stains (variation of tonality) on rocks that presents very low porosity. It can also be noted that the EO of Mp has the broadest spectrum of activity. The results allow considering the use of Mp, Fv, Lv, and Tm EOs as valid alternatives to commercial biocides, providing a prospective application in the field of green conservation of building heritage.

Unraveling disparate roles of organisms, from plants to bacteria, and viruses on built cultural heritage

The different organisms, ranging from plants to bacteria, and viruses that dwell on built cultural heritage can be passive or active participants in conservation processes. For the active participants, particular attention is generally given to organisms that play a positive role in bioprotection, bioprecipitation, bioconsolidation, bioremediation, biocleaning, and biological control and to those involved in providing ecosystem services, such as reducing temperature, pollution, and noise in urban areas. The organisms can also evolve or mutate in response to changes, becoming tolerant and resistant to biocidal treatments or acquiring certain capacities, such as water repellency or resistance to ultraviolet radiation. Our understanding of the capacities and roles of these active organisms is constantly evolving as bioprotection/biodeterioration, and biotreatment studies are conducted and new techniques for characterizing species are developed. This brief review article aims to shed light on interesting research that has been abandoned as well as on recent (some ongoing) studies opening up new scopes of research involving a wide variety of organisms and viruses, which are likely to receive more attention in the coming years. KEY POINTS: • Organisms and viruses can be active or passive players in heritage conservation • Biotreatment and ecosystem service studies involving organisms and viruses are shown • Green deal, health, ecosystem services, and global change may shape future research.

The Potential Use of Microorganisms as Restorative Agents: An Update

The biodeterioration process involves every type of Cultural Heritage item, including monuments, stoneworks, frescoes, and easel paintings. The accurate study of the microbial and fungal communities dwelling on artworks, and involved in their deterioration, is essential for the adoption of optimal prevention and conservation strategies. Conventional restorative methods, that usually involve chemical and physical technologies, present some disadvantages, including short-term and unsatisfactory effects, potential damage to the treated works, human toxicity, and environmental hazards. Research in the field of restoration has paved the way for innovative biological approaches, or ‘biorestoration’, in which microorganisms are not only considered as an eventual danger for artworks, but rather as potential tools for restoration. The present review describes the main aspects of the biodeterioration process and highlights the most relevant biorestoration approaches: bioconsolidation, biocleaning, biological control, and new promising bio-decontaminating compounds.

Green mitigation strategy for cultural heritage: bacterial potential for biocide production

Several biosurfactants with antagonistic activity are produced by a variety of microorganisms. Lipopeptides (LPPs) produced by some Bacillus strains, including surfactin, fengycin and iturin are synthesized nonribosomally by mega-peptide synthetase (NRPS) units and they are particularly relevant as antifungal agents. Characterisation, identification and evaluation of the potentials of several bacterial isolates were undertaken in order to establish the production of active lipopeptides against biodeteriogenic fungi from heritage assets. Analysis of the iturin operon revealed four open reading frames (ORFs) with the structural organisation of the peptide synthetases. Therefore, this work adopted a molecular procedure to access antifungal potential of LPP production by Bacillus strains in order to exploit the bioactive compounds synthesis as a green natural approach to be applied in biodegraded cultural heritage context. The results reveal that the bacterial strains with higher antifungal potential exhibit the same morphological and biochemical characteristics, belonging to the genera Bacillus. On the other hand, the higher iturinic genetic expression, for Bacillus sp. 3 and Bacillus sp. 4, is in accordance with the culture antifungal spectra. Accordingly, the adopted methodology combining antifungal screening and molecular data is represent a valuable tool for quick identification of iturin-producing strains, constituting an effective approach for confirming the selection of lipopeptides producer strains.