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.

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MamC from Magnetococcus marinus MC-1 has been shown to control the size of magnetite crystals in in vitro experiments, thereby demonstrating its potential as a candidate protein for the production of magnetite nanoparticles possibly useful in medical and other applications. However, the importance of the structure and aggregation state of the protein on the resulting biomimetic nanoparticles has not yet been assessed. One method normally used to prevent the aggregation of integral membrane proteins is the introduction of detergents during protein purification. In this study, results from protein aggregation following the addition of Triton-X100, DDM, and LDAO are presented. Magnetite particles formed in the presence of MamC purified using these three detergents were compared. Our results show that detergents alter the structure of the folded recombinant protein, thus preventing the ability of MamC to control the size of magnetite crystals formed chemically in vitro. Furthermore, we show that the introduction of detergents only at the dialysis process during the protein purification prevents its aggregation and allows for correct, functional folding of MamC. These results also indicate that the population of the active protein particles present at a certain oligomeric state needs to be considered, rather than only the oligomeric state, in order to interpret the ability of magnetosome recombinant proteins to control the size and/or morphology of magnetite crystals formed chemically in vitro.

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