Carotenoids produced by halophilic bacterial strains on mural paintings and laboratory conditions

Abstract

Due to the presence of efflorescences and improper microclimate conditions for conservation, pink-pigmented areas were reported in two historic monuments in Northern and Central part of Romania. The aims of the present study were to find the nature of pink pigments observed on the pictorial layer, original and infilling mortar, to investigate the presence of carotenoids both on mural paintings and in the isolated halophilic bacterial strains and to preliminary characterize and identify the producing strains. Their role in the aesthetical biodeterioration of historic monuments was also pointed out. Obtained Raman spectra of the pink pigments extracted both from the isolated bacterial cultures (molecularly identified as mostly related to Halobacillus hunanensis and Halobacillus naozhouensis) and from the mural painting samples contain diagnostic bands of carotenoids. These results were confirmed by FTIR spectroscopy. The strong Raman signal of bacterial carotenoids detected on mural painting indicated their potential use as biomarker molecules in the evaluation of contamination and state of conservation of mural paintings and lithic monuments. Our results contribute to opening a new direction in cultural heritage restoration to assess the conservation status on the basis of interdisciplinary research, starting with spectroscopic methods (Raman, FTIR) and confirmed by microbiological analysis.

The Bad and the Good—Microorganisms in Cultural Heritage Environments—An Update on Biodeterioration and Biotreatment Approaches

“…Analyses of microorganisms associated with biodeterioration or biotreatment processes are more meaningful if auxiliary techniques, which visualize structural modifications or chemical changes, are applied. It has already been shown, that for complex multi-component analyses several commonly acknowledged techniques may be combined, e.g.,: (i) XRF, XRD, SEM, FM, isotope analyses, coupled with cultivation experiments on Reasoner’s 2A agar and 16S rDNA analyses (Applied Biosystems platform) [ 71 ]; (ii) SEM, RS, FTIR, together with cultivation experiments on Mueller–Hinton medium and 16S rDNA analyses (Applied Biosystems platform) [ 72 ]; (iii) XRD, RS, FTIR, SEM-EDS, confocal microscopy, accompanied with transcriptomic sequencing (Illumina) and shotgun sequencing (PacBio) [ 52 ].…”

“…These methods enable the monitoring of microbial contamination and the state of artwork by spectra identification. They have already been employed for the analyses of pigment [ 72 ], textile fibers [ 73 , 74 ], mineral formation [ 52 ], and other natural organic substances such as oils, gums or glues [ 75 ]. One of the newest methodologies, allowing for early detection of microorganism activity is a technique using RGB-ITR laser scanner (Red Green Blue Imaging Topological Radar) [ 76 ].…”

“…Mural paintings are habitats with limited nutrient content compared to canvas paintings, however they are still colonized by microorganisms such as Gloeocapsa sp., Rubrobacter sp., Aspergillus sp., and Penicillium sp. [ 72 , 95 , 96 , 97 , 109 ]. These microorganisms are among many others which contribute to the biodeterioration processes, manifested as discoloration, bulging plaster, or peeling pictorial layer.…”

Characterisation of a carotenoid producing extremely halophilic archaeon Halorubrum sodomense MS5.1 isolated from a solar saltern in Tamil Nadu, South India

“…Pigment extraction was done as per Cojoc et al (2019). Biomass from 50 ml of culture was centrifuged at 7200 g for 15 min and washed with 30% saline broth twice by centrifugation.…”

Isolation, Characterization, and Applicability of Helveticin 34.9, A Class Iii Bacteriocin Produced By Lactobacillus Helveticus 34.9

“…To determine the activity spectrum of L. helveticus 34.9 bacteriocin, several bacterial strains were used as indicator, including other LAB, some bacterial pathogens, and a strain of Halobacillus hunanensis, namely 5Hum, previously isolated from the degraded wall of a Romanian monastery (Cojoc et al 2019).…”