Bioprecipitation of calcium carbonate by Rhodococcus erythropolis

The decay of stone cultural heritage monuments has led to the exploration of new conservation methods. Among them, bio-conservation-especially bacterial calcium carbonate precipitation-has emerged as a promising alternative to traditional limestone restoration techniques. The extracellular polymeric material (EPM) substance is an organic polymeric matrix secreted by microorganisms with several key properties and functions. EPM is chemically complex, consisting of exopolysaccharides (EPS), proteins, and extracellular DNA, with a variable composition depending on bacterial species/strains and culture conditions. This study investigated the role of bacterial EPS, e.g., capsular polysaccharides (CPS) and the associated protein components in calcium carbonate precipitation and evaluated the influence of calcium ions in cultural media on protein expression in the CPS fraction from Rhodococcus erythropolis. Capsular polysaccharides were isolated from R. erythropolis grown in culture media in the presence or absence of calcium ions. The results showed that calcium ions in cultural media can modulate the protein composition of the exopolymeric substance produced by bacterial cells. Moreover, the test in vitro indicated the calcifying ability of some proteins with a molecular weight in the 60-70 kDa range isolated by the CPS fraction extracted from bacterial strain grown on a liquid medium in the presence of calcium ions.