A Novel Approach to Isolation and Screening of Calcifying Bacteria for Biotechnological Applications

Paola Cacchio,Maddalena Del Gallo

doi:10.3390/geosciences9110479

Abstract

Bacterial calcium-carbonate precipitation (BCP) has been studied for multiple applications such as remediation, consolidation, and cementation. Isolation and screening of strong calcifying bacteria is the main task of BCP-technique. In this paper, we studied CaCO3 precipitation by different bacteria isolated from a rhizospheric soil in both solid and liquid media. It has been found, through culture-depending studies, that bacteria belonging to Actinobacteria, Gammaproteobacteria, and Alphaproteobacteria are the dominant bacteria involved in CaCO3 precipitation in this environment. Pure and mixed cultures of selected strains were applied for sand biocementation experiments. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses of the biotreated samples revealed the biological nature of the cementation and the effectiveness of the biodeposition treatment by mixed cultures. X-ray diffraction (XRD) analysis confirmed that all the calcifying strains selected for sand biocementation precipitated CaCO3, mostly in the form of calcite. In this study, Biolog® EcoPlate is evaluated as a useful method for a more targeted choice of the sampling site with the purpose of obtaining interesting candidates for BCP applications. Furthermore, ImageJ software was investigated, for the first time to our knowledge, as a potential method to screen high CaCO3 producer strains.

Highlights

In natural environments, chemical CaCO3 precipitation is accompanied by microbial processes involving bacteria, cyanobacteria, archaea, small algae, and fungi [1]
Since Bacterial calcium-carbonate precipitation (BCP) is influenced by the metabolic activity of the bacteria, we investigated through the Biolog EcoPlates the metabolic activity of the bacterial communities dwelling a rhizospheric soil, with the purpose of choosing a good sampling site for an efficient calcifying bacteria screening
In the literature there is a lot of information about the possibilities of using the Biolog EcoPlates to analyze functional microbial diversity in the presence of different plant and cultivation type, and to study the metabolic activity of microorganisms in soils contaminated with pesticides and heavy metals

Summary

Introduction

Chemical CaCO3 precipitation is accompanied by microbial processes involving bacteria, cyanobacteria, archaea, small algae, and fungi [1]. Chemical CaCO3 precipitation is a rather straightforward process governed mainly by concentration of non-precipitated calcium, concentration of the total inorganic carbon, pH, and availability of nucleation sites for CaCO3 crystal formation [16,17,18] Bacteria can alter these factors, either separately or in combinations with one another, in a number of ways linked to cell surface structures and metabolic activities [16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36]. These different metabolic processes increase pH and/or dissolved inorganic carbon concentration, favoring CaCO3 precipitation

Methods

Results

Conclusion