Bioconservation of Deteriorated Monumental Calcarenite Stone and Identification of Bacteria with Carbonatogenic Activity

Abstract

The deterioration of the stone built and sculptural heritage has prompted the search and development of novel consolidation/protection treatments that can overcome the limitations of traditional ones. Attention has been drawn to bioconservation, particularly bacterial carbonatogenesis (i.e. bacterially induced calcium carbonate precipitation), as a new environmentally friendly effective conservation strategy, especially suitable for carbonate stones. Here, we study the effects of an in situ bacterial bioconsolidation treatment applied on porous limestone (calcarenite) in the sixteenth century San Jeronimo Monastery in Granada, Spain. The treatment consisted in the application of a nutritional solution (with and without Myxococcus xanthus inoculation) on decayed calcarenite stone blocks. The treatment promoted the development of heterotrophic bacteria able to induce carbonatogenesis. Both the consolidation effect of the treatment and the response of the culturable bacterial community present in the decayed stone were evaluated. A significant surface strengthening (consolidation) of the stone, without altering its surface appearance or inducing any detrimental side effect, was achieved upon application of the nutritional solution. The treatment efficacy was independent of the presence of M. xanthus (which is known as an effective carbonatogenic bacterium). The genetic diversity of 116 bacterial strains isolated from the stone, of which 113 strains showed carbonatogenic activity, was analysed by repetitive extragenic palindromic-polymerase chain reaction (REP-PCR) and 16S rRNA gene sequencing. The strains were distributed into 31 groups on the basis of their REP-PCR patterns, and a representative strain of each group was subjected to 16S rRNA gene sequencing. Analysis of these sequences showed that isolates belong to a wide variety of phylogenetic groups being closely related to species of 15 genera within the Proteobacteria, Firmicutes and the Actinobacteria. This study shows that the abundant carbonatogenic bacteria present in the decayed stone are able to effectively consolidate the degraded stone by producing new calcite (and vaterite) cement if an adequate nutritional solution is used. The implications of these results for the conservation of cultural heritage are discussed.

Influence of Substrate Mineralogy on Bacterial Mineralization of Calcium Carbonate: Implications for Stone Conservation

“…This was not unexpected. The formation of calcium carbonate in such a medium has been reported for M. xanthus (4,69,70) and B. diminuta (40), as well as for the bacterial community inhabiting weathered calcarenite stones (38,40) and undecayed quarry calcarenite stones (39). Studies performed since the beginning of the 20th century demonstrate that numerous heterotrophic bacteria induce the precipitation of calcium carbonate in a range of natural environments and laboratory culturing conditions (references 31 and 69 and references therein).…”

“…B. diminuta (strain SJ 63) was found to be the most effective of all carbonatogenic bacteria (more than 100 species) isolated from this historic building at producing calcium carbonate in M-3P medium. Details on bacterial isolation, identification, and carbonatogenic capacity have been presented elsewhere (40).…”

“…Bacterial mineralization of calcium carbonates has found applications in the remediation (fixation) of metalcontaminated soil and groundwater (87), atmospheric CO 2 sequestration (21, 59), the strengthening and consolidation of soil and sand (14), the reduction of the porosity and/or permeability of geological formations (24, 29), the protection and repair of concrete and cement structures (15,66), and the conservation of building stone and statuary (16,19,30,38,39,40,47,69,84,88,94). Recently, bacterial precipitation of fluorescent calcium carbonate, with potential applications as a filler in rubber, plastics, and stationery ink and as a fluorescent marker, has been reported (93).…”

Application of bacteria in concrete: a critical evaluation of the current status

“…Tiano et al [27] and Jroundi et al [28] also applied biomineralization for on-site conservation of decayed stones. De Muynck et al [29] measured the strengthening effect of biodeposition on Maastricht limestone by means of the drilling resistance measurement system (DRMS Cordless SINT Technology, Italy).…”

Effective Use of Plant-Derived Urease in the Field of Geoenvironmental/ Geotechnical Engineering

“…It has a possibility to apply the plant-derived urease induced carbonate precipitation technique to create a consolidated surface layer by spraying the biogrout solution straight onto the surface of the buildings or statuaries in order to prevent further erosion. This kind of preservation would take place through the strengthening of the existing bonds of the sediments in the existing stone [116]. With rapid urbanization, soil and water pollution are threatening not only to human health but also to the entire living organisms in environment.…”