جستجوی مقالات مرتبط با کلیدواژه « سیمان زیستی » در نشریات گروه « زیست شناسی »

Background & Calcite precipitation by microbial stimulation (MICP) is the new method which used for soil stabilization and solidity. Biocementation is an ecological process based on microbial urease enzyme activity. The present study aimed to isolation and identification of Bacillus spp. with MICP potential from various ecosystems of Iran.Materials & This cross-sectional study was conducted on 200 soil samples collected from arid and desert ecosystems of Iran. Bacillus were isolated and characterized by conventional microbiology tests and molecular methods include the amplification and sequences analysis of gyrA and 16S rRNA genes. Growth in presence of urea, different salinity, pH and temperature, also SEM, XRD and wind tunnel analysis were used to determine biocementation ability. A total of 5 Bacillus isolate with strong urease activity belonging to 4 different species include B. amyloliquefaciens, B. thuringiensis, B. carboniphilus and B. oleos were identified. Optimum conditions for MICP by isolates are 35°C, pH 8.8 and 6% salinity. Moreover, the results of wind tunnel after MICP showed a 100-fold reduction in soil loss at a flow rate of 100 km/h. The results showed that indigenous Bacillus spp. have a significant potential to produce bio-cement. Therefore, its suggest the MICP process have been used to reduce soil losses due to wind erosion, stabilization of loose sands and ground consolidation in the desert soils of the country.

Urease-producing bacteria can precipitate calcite nano-crystals by producing urease in the presence of urea and calcium. Calcite precipitation resulting from microbial activity is a process which causes cementation of soil particles in nature. The purpose of this study was to isolate urease-producing halophilic bacteria in order to precipitate calcite in saline soil. Natural samples, including soil and saline waters, were selected for this purpose. At First, halophilic bacteria were isolated by salt-containing TSB medium. Then, a selective medium containing phenol red and urea facilitated the isolation of urease-producing bacteria. Hydrolysis of urea by urease causes alkalization of the medium and the formation of pink halo around colonies. Finally, the best isolate was selected for further study by measuring the release of ammonium by the Nessler method. The ability or inability of isolates to produce calcite was investigated by culturing the isolates on sedimentary medium with different salt concentrations for 10 days. In total, 110 halophilic isolates were isolated, among which 58 isolates had the ability of urease production. The microscopic studies of colonies showed that only 6 isolates were able to produce crystals on precipitation medium. Isolate 6 was selected for further study and then analyzed by X-ray diffraction crystals on precipitation medium. Isolate 6 was selected for further study and then analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM) equipped with an energy dispersive X-ray (EDX) detector. Studies of urease activity showed that this strain released 20.86 mM ammonium after 18 hours. This bacterium was identified by biochemical and molecular analyses and the comparison of its 16S rRNA gene sequence showed 99.92% similarity with the similar gene sequence in Staphylococcus xylosus and then this sequence was submitted in NCBI database with the accession number MG655155. This isolate was able to produce calcite in free salt medium, with salinity up to 10%. Nowadays, many efforts have been made to produce environmental-friendly cements, and therefore, the use of urease-producing halophilic bacteria is an appropriate candidate for bio-cementing in saline environments.

With urbanization expansion, application of concrete and construction materials is widely increasing throughout the world. Therefore, the use of a mechanism that can effectively extend the life of concrete structures is essential. Durable reinforced concrete structures are generally affected by the crack. Cracks in concrete are caused due to various reasons such as an environmental attack, overloading or accidental damage. Surface cracks in concrete facilitate the penetration of chemicals and corrosive chlorine, so as a result of these factors steel rebars corroded and caused the destruction of concrete structures. Calcium carbonate precipitates have proved their ability as a microbial sealant to fill the cracks and the gaps in Granites and sand. In this method, urea is hydrolyzed by the urease secreting bacteria and calcium carbonate is formed in the presence of calcium ion, which improves the stability and properties of concrete in the long term. Therefore, the use of microbial precipitation in concrete restoration can be considered as a natural and environmentally friendly strategy. This paper reviews current progress and potential of this technology.

Microbially induced carbonate precipitation (MICP) is one of the proposed methods for soil stabilization and strengthening. The aim of this study was to isolate and characterize biocement-producing ureolytic bacteria from arid soils.
In this cross-sectional descriptive study, 280 soil samples were collected from different areas of Iran. Samples were cultured using urea broth medium. Urease-positive bacteria were assessed for the level of urease activity. Identification of active strains was performed based on conventional biochemical tests and 16S rRNA gene sequencing. Optimum temperature and pH conditions for biocement production were evaluated in urease-positive
bacteria and was compared with sporosaicina pasteurii (ATCC 11589) strain. Finally, calcium carbonate crystals were assessed byX-ray diffraction (XRD) crystallography test at the temperature of 25 °C and pH of 8.5 as optimal conditions.
304 strains were isolated from 5 different bacterial genera. Bacillus and Sporosarcina were the major ureolytic isolates of arid regions. The most amount of calcium carbonate was produced at the temperature of 25 °C and a pH of 8.5. Ten most effective isolates in the production of urease enzymes and biocement were identified by molecular analysis and subsequently registered in NCBI Genbank. In addition, biocement production by selected isolates was confirmed by XRD test.
Our results showed that the amount of urea and calcium chloride plays an important role in calcium carbonate crystals production. S. pasteurii was one of the most important biocement-producing bacteria. Therefore, optimization of growth conditions in higher scale is recommended for further applications in stabilizing the sand, ground strength and bridging