## 3 Effectiveness of the Consolidated Stone in the Environment
### Biodeterioration Testing and Colonization of Biocalcite  
There have been few studies on the colonization of the newly produced material by environmental microorganisms, although a recent article reviews the methodologies employed to assess the durability of cultural heritage stone surfaces in response to microbial colonization [92]. Recolonization after the use of non-biological consolidants on marble, sandstone and plaster in the archeological site of Fiesole, Italy, was shown to depend mainly on the bioreceptivity of the substrate and the climatic conditions [93]. A relatively recent paper suggests that the bioconsolidation treatment based on stimulation of indigenous calcifying microorganisms does not significantly alter the stone microbiota in the long term [94]. The authors showed, using DGGE monitoring of the stone-autochthonous microbiota before and at 5, 12 and 30 months after bioconsolidation with autochthonous bacteria, that the _Actinobacteria_ that were initially completely dominant decreased to 44.2% after 5 months. After 12 months, _Cyanobacteria_ (22.1%) appeared and remained dominant until thirty months. Thereafter, the population consisted of _Actinobacteria_ (42.2%) and _Cyanobacteria_ (57.8%). For the fungi, the _Ascomycota_ phylum was dominant before treatment (100%), _Basidiomycota_ (6.38%) appeared after five months, but disappeared after 12 months. After 30 months the fungal population started to stabilize and _Ascomycota_ again dominated (83.33%). Green algae (Chlorophyta, Viridplantane) were rare colonizers of the new material.  
The results of this study indicated that final changes to the initial microbial populations were relatively small.  
For many years, the only tests carried out on bioconsolidated stone were physical and chemical examinations, which gave information about the strength and chemical structure of the new material. There was no definitive knowledge about the ability of biocalcite to withstand the biological attacks to which it would be subjected in the environment. Indeed, [PERSON] et al. [72] state that \"It is unknown whether such a treatment is effective and does not produce any deleterious side effects under extreme hot and humid environmental conditions typical for the Maya area where... the potential for microbial biodeterioration is very high\". In 2015, however, [PERSON] et al. [95] subjected fiber cement panels, treated in various ways to produce a surface layer of biocalcite, to biodeterioration testing in the hot and humid climate of Sao Paulo, Brazil. They found that the calcite formed by treatment with living _Bacillus sphaericus_ LMG 222 57 plus urea plus B4 medium was the most resistant to the aesthetic biodeterioration that occurred within the 22 months of exposure. This resistance was correlated with lower water absorption and porosity, together with surface hydrophilicity, all linked to the smaller size of the biocalcite crystals. There was no apparent degradation of the crystals within the timescale of the test. Though promising, longer term experiments, often spanning several years, are necessary to truly know the extent of resistance of biocalcite to microbial attack under various environmental conditions.