Study on the Remediation of Cd Pollution by the Biomineralization of Urease-Producing Bacteria

Abstract

Cadmium (Cd) is a highly toxic metal that can affect human health and environmental safety. The purpose of this study was to research the removal of Cd from an environmental perspective. In this article, four highly urease-active strains (CZW-2, CZW-5, CZW-9 and CZW-12) were isolated from an abandoned mine and their phylogenetic trees were analyzed. The maximum enzyme activities, the mineralized precipitate and the removal rates of these strains were compared. The results showed that CZW-2 had the highest urease activity at 51.6 U/mL, and the removal rates of CZW-2, CZW-5, CZW-9 and CZW-12 after 120 h were 80.10%, 72.64%, 76.70% and 73.40%, with an initial concentration of Cd of 2 mM in the Cd precipitation experiments. XRD (X-ray diffractometer), EDS (Energy dispersive spectrometer) and FTIR (Fourier transform infrared spectroscopy) analysis indicated that the mineralized precipitate was CdCO3. SEM (Scanning electron microscopy) analysis revealed that the diameter of the oval-shaped mineralized product ranked from 0.5 to 2 μm. These strains were used to remedy Cd-contaminated soil, and five different fractions of Cd were measured. Compared with the control, the results of spraying pre-cultured strains containing 2% urea to remove Cd from contaminated soils showed that the exchangeable fraction of Cd decreased by 53.30%, 27.78%, 42.54% and 53.80%, respectively, whereas the carbonate-bound fraction increased by 55.42%, 20.27%, 39.67% and 34.36%, respectively, after one month. These data show that these strains can effectively reduce the bioavailability and mobility of Cd in contaminated soils. The results indicate that biomineralization based on the decomposition of substrate urea can be applied to remedy heavy contaminated soil and water.

Biomineralization of calcium carbonate by marine bacterial strains isolated from calcareous deposits

“…Both enzymatic pathways, urease and carbonic anhydrase, have often been studied separately as inducing biomineralization [10,15,23,31,32] but it is possible that a coupling of these 2 ways would allow better biocalcification in some bacteria [18,19,33]. The urease pathway would provide an alkalinisation around the cells by hydrolysis of urea and the carbonic anhydrase pathway would provide an additional source of HCO 3…”

“…The most widely studied metabolic pathway is urea hydrolysis driven by bacterial urease, which leads to an alkalization of the medium inducing precipitation of CaCO 3 [8,[10][11][12]. This metabolism could be applied in particular to the repair of concrete building materials [13], the stabilization of soils [14], the depollution of materials contaminated with heavy metals [15] and the consolidation of sandy substrate [16,17]. Carbonic anhydrase enzymes are also involved in the formation of CaCO 3 precipitates under natural conditions and can act synergistically with urease [18,19].…”

Functional Analysis of Organic Acids on Different Oilseed Rape Species in Phytoremediation of Cadmium Pollution

“…Heavy metal pollution in the soil is a widespread phenomenon, especially Cd pollution, which seriously affect the development of agriculture, so it is urgent to seek effective repairing methods [ 38 ]. Phytoremediation is now the mainstream of soil remediation, and the single repairing method has its limitations [ 39 ].…”

Screening of Heavy Metal-Immobilizing Bacteria and Its Effect on Reducing Cd2+ and Pb2+ Concentrations in Water Spinach (Ipomoea aquatic Forsk.)

“…In recent years, heavy metal-immobilizing bacteria have been widely studied and applied as excellent heavy metal passivators. Heavy metal-immobilizing bacteria not only immobilize heavy metals, alter the existing state of heavy metals in soil, and reduce the absorption of heavy metals by crops, but also promote the growth of crops and improve the quality of crops [13,18]. Bacteria increased the growth and heavy metal resistance of vegetables by producing indole acetic acid (IAA), siderophores, 1-aminocyclopropane-1-carboxylate deaminase, and arginine decarboxylase.…”