ISOLATION, IDENTIFICATION, DIFFERENTIATION AND SCREENING OF LOCAL AEROBIC UREOLYTIC BACTERIA INVOLVED IN MICROBIALLY INDUCED CALCIUM CARBONATE PRECIPITATION IN QATARI SOIL.

Abstract

Biomineralization plays an important role in stabilizing the soil by modifying its geological and physical properties, hence, acting as a stabilizer against wind erosion specially in regions characterized by harsh soil (calcareous and dry) and weather such as the Arabian Gulf. Among the micro-organisms existing in soil, ureolytic bacteria can modify the characteristics of soil, thereby inducing biotic mineralization. One of the aim of this study was to explore the occurrence and diversity of ureolytic bacteria in soils of Qatar, for further application in soil stabilization, among other applications. The focus was to study the potential of bacteria adapted to the harsh environmental conditions to exhibit urease activity. Indigenous bacteria were isolated from six locations across Qatar. The most common genus found to exhibit ureolytic activity was Bacillus while the most common species was Bacillus cereus. 18 isolated ureolytic bacteria were identified and differentiated by MALDI-TOF MS while for 6 isolates, molecular 16S rRNA technique was used. All isolates were screened for the urease activity based on a modified method optimized in this work. Arbitrary urease activity (AUA) and specific production (AUA/cfu) were considered as main screening parameters. The isolates with high specific production of ureolytic activity are considered as inducer of calcium carbonate formation. The analysis of precipitates obtained in cultures using SEM-EDS analysis showed the precipitates of calcium carbonates while XRD analysis confirmed the presence of calcium carbonate in two mineral phases: aragonite and calcite. The quantification of CaCO3 precipitated was done using back-titration and by analysis of calcium ions using atomic absorption spectrometer. Under lab conditions, the process of Microbial induced calcite precipitation (MICP) increased the calcium carbonate content to 142.96 mg/g of soil (acid treated) in 20 mL liquid cultures quantified by titration, however, bacteria were able to induce 29 mg of CaCO3 per gram of natural soil. The application of MICP on large scale was done in Qatar University Al-Khor farm where an increase in the CaCO3 content was quantified to be of 16.2 %. This research illustrated high occurrence and distribution of indigenous Bacillus sp. in soil of Qatar that are capable of biomineralization and hence, can be proved helpful if properly utilized in enhancement of soil properties.