## 2 Bioconsolidation Techniques
### Microbial Cells in Bioconsolidation Treatments
Fatty acid metabolism has also been implicated by work that showed how CaCO\({}_{3}\) precipitation in _Lysinobacillus_ could modify membrane rigidity by upregulating branched chain fatty acid synthesis [65; 66]. Figure 1: Limestone wall in Campeche, southern México, exhibiting a range of deterioration pathologies. Formers are being used to demarcate panels prior to treatment by spraying with carbonatogenic bacterial suspension or control solution. Replicate panels will allow statistical analysis. The aim is to increase surface hardness and reduce the detachment rate of flaking material. The prospects for the future are promising, with the combined use of improved culturing methods and metabolomics-based selection of novel carbonatogenic species. The study of their physiology and ecology should enhance the success of bioconsolidation strategies, in particular for long-term application. Of course, other factors affect bioclcite precipitation, apart from the particular microbial species. These are cell and nutrient concentrations, source of calcium, presence of other substances, such as surfactants used as dispersants [55] and salt [24], and methods used to inoculate the bacteria onto the stone surfaces. There are several publications around this topic [31; 67; 68; 69]. The alternative to application of selected carbonatogenic bacteria is to try to stimulate those already present on the stone surface. [PERSON] et al. [70] tested this approach in vitro, immersing porous limestone slabs in a nutrient medium. The positive result obtained was shown to be due to ammonification of the medium. Later, a similar approach was adopted by [PERSON] et al. [71] for the consolidation of badly degraded tuff stone and lime plaster at the Mayan site of Copan (Honduras). The stone was treated with patented (sterile) M-3P nutrient solution containing amino acids and calcium. This resulted in significant changes in the indigenous bacterial community, which were detected using NGS techniques. There were increased levels of _Arthobacter_, _Micrococaceae_, _Nocardioides_, _Fictibacillus_, _Streptomyces_ and _Rubobacter_. In the lime plaster, _Bacillus_, _Agrooccus_, and _Microacterium_ were the major genera after treatment. It is notable that most of the increased components of the community after treatment were capable of calcium carbonate biomineralization. Although this may indicate that the treatment could replace application of living microorganisms, the detection of bioclcifying microorganisms does not necessarily imply that these will produce a good consolidating performance, and further testing, such as that suggested in Table 2 below, would be necessary. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \begin{tabular}{c} **Consolidating** \\ **Properties** \\ \end{tabular}  & \begin{tabular}{c} **Consolidation** \\ **Action** \\ \end{tabular}  & **Substrate** & \begin{tabular}{c} **Consolidation** \\ **Treatments** \\ \end{tabular}  & \begin{tabular}{c} **Evaluation of** \\ **Treatment** \\ \end{tabular}  \\ \hline \multirow{4}{*}{**Effectiveness**} & \multirow{4}{*}{ \begin{tabular}{c} Penetration \\ depth \\ \end{tabular}  } & \begin{tabular}{c} Marble, \\ limestone, and \\ lime-based \\ mortars \\ \end{tabular}  & \begin{tabular}{c} Phosphate \\ treatment based \\ on \\ Hydroxyapatite \\ (HAP) \\ Ethyl silicate \\ (ES) \\ \end{tabular}  & \begin{tabular}{c} Scanning \\ electron \\ microscopy \\ (SEM) \\ \end{tabular}  \\ \hline \multirow{4}{*}{**Compatibility**} & \multirow{4}{*}{ \begin{tabular}{c} Morphology and \\ microstructure \\ of samples \\ resulting from \\ applied products \\ \end{tabular}  } & \multirow{4}{*}{ \begin{tabular}{c} Nano-solution of \\ calcium tetrahydrofurfuryloxide \\ (Ca (OTHF)2) \\ \end{tabular}  } & \multirow{4}{*}{ \begin{tabular}{c} Optical \\ Microscopy \\ (OM) and \\ Scanning \\ Electron \\ Microscopy \\ with Energy \\ Dispersive X-ray \\ spectroscopy \\ (SEM-EDX) \\ \end{tabular}  } \\ \hline \multirow{4}{*}{**Effectiveness**} & \multirow{4}{*}{\