Application of calcifying bacteria for remediation of stones and cultural heritages

Abstract

Since ages, architects and artists worldwide have focused on usage of durable stones as marble and limestone for construction of beautiful and magnificent historic monuments as European Cathedrals, Roman, and Greek temples, Taj Mahal etc. But survival of these irreplaceable cultural and historical assets is in question these days due to their degradation and deterioration caused by number of biotic and abiotic factors. These causative agents have affected not only the esthetic appearance of these structures, but also lead to deterioration of their strength and durability. The present review emphasizes about different causative agents leading to deterioration and application of microbially induced calcium carbonate precipitation as a novel and potential technology for dealing with these problems. The study also sheds light on benefits of microbial carbonate binders over the traditional agents and future directions.

Keywords: bacteria; biofilm; calcite; extrapolymeric substances; limestone; microbial carbonates; urease.

Figure 1

Bacteria serving as nucleation site for CaCO₃ precipitation in the substrate particles. Calcium ions in the solution are attracted to the bacterial cell wall due to its negative charge. When urea is added to bacteria, dissolved inorganic carbon (DIC) and ammonium (AMM) are released in the microenvironment of the bacteria. In the presence of calcium ions, this leads to local supersaturation and finally there is precipitation of calcium carbonates which act as binder between loose substrate particles (Source: DeJong et al., 2010).

Figure 2

Colonies of 6 different strains of B. sphaericus and B. lentus on agar plates and their ability to encrust themselves in calcium carbonate (Source: Dick et al., 2006).

Figure 3

Scanning electron microscopy (SEM) observations of Carbogel without (left) and with (right) D. vulgaris subsp. vulgaris ATCC 29579 cells (Source: Cappitelli et al., 2006).