Calcinating Bacteria in Extreme Ecosystems of the Southern Aral Region

-The processes of microbially induced precipitation of calcium carbonates are widespread in natural environments and are an important part of the biogeochemical carbon cycle. These processes comprised the basis of new "biocementation" technologies, which are extensively developing worldwide during the last decade. These technologies are aimed at designing the novel "self-healing" construction materials, as well as at maintaining the strength of various buildings and structures. Since the optimal conditions for calcite formation are high salinity and alkalinity, the search for calcifying microorganisms in a variety of ecosystems, including extreme ones, is of interest. At present, many strains of halophilic and halotolerant bacteria, that induce calcination, have already been isolated and tested in pilot industrial processes. Most of these bacteria possess urease activity, which is the main contributor to the binding of calcium ions to insoluble carbonate. A wide variety of natural ecosystems with optimal conditions for the development of calcifying urobacteria, as well as the economic demand for biocementation technologies, stimulate interest in the search for more and more novel strains of these microorganisms. One of the promising resources to be screened for such organisms is the ecosystem of the drying Aral Sea and the adjacent desert and semi-desert Aral region. Here we present the results of screening various extreme ecosystems of the Aral region for the presence of calcifying microorganisms. We obtained 28 pure cultures of heterotrophic aerobic bacteria from samples of plant residues and soils of the Aral Sea region, 4 of which had urease and calcifying activities. Their activities were compared with those of the strains presently used to produce biocementing mixtures. We have identified the phylotypes of putative calcifying microorganisms in microbial communities of desert soil, thermal waters, and bottom sediments of a salt lake, and described the phylogenetic diversity of these communities. Our results indicated the wide distribution of calcifying microorganisms in the ecosystems of the South Aral region and highlighted the expediency of screening them for the new biotechnologically relevant strains of these organisms.