Microbial Induced Calcite Precipitation (MICP) Potential of Ureolytic Bacillus sp. Isolated from the Soil of Eroded Ecosystems for Stabilizing and Improving the Fertility of Eroded Soils

Abstract

The loss of soil from lands due to erosion has a negative effect on ecosystems and food security. Bacillus due to high catabolic capability is an appropriate candidate for application in biocementation process. The aim of this study is isolate and characterize Bacillus sp. with biocementation capability from various ecosystems. The isolates were separated from 400 samples, and characterized by biochemical and molecular methods include the amplification and sequencing analysis of gyrA and 16S rRNA genes. Growth in presence of urea, in different salinity, pH, and temperature, also scanning electron microscope (SEM), X-ray diffraction (XRD), and wind tunnel analysis were applied to determine biocementation ability. A total number of 195 isolates were recovered from environmental samples, of which 25 isolates (12.82%) were identified as urease-positive Bacillus which belonged to 10 species consisting of Bacillus subtilis five strains (20%), Bacillus vallismortis and Bacillus seohaeanensis four strains (16%) each, Bacillus mobilis, Bacillus pseudofirmus, Bacillus cohnii, Bacillus cereus, Bacillus alkalinitrilicus two strains (8%) each, and Bacillus sphaericus and Bacillus megaterium one strain (4%) each. Moreover, 15 urease-positive isolates (7.7%) belonging to Ralostenia, Actinomycete, and Halomonas genera were identified. Optimum conditions for microbial induced calcite precipitation (MICP) by isolates are 30 °C, pH 9, and 6% salinity. The highest rate of calcium carbonate formation and urease activity recorded in B. subtilis with 24.15 mg/mL of calcium carbonate and 4.40 × 103 unit/L of urease, followed by B. mobilis and B. alkalinitrilicus with 22.85 mg/mL of calcium carbonate and 3.93 × 103 unit/L of urease. After MICP the lowest soil loss ratio at a flow rate of 90 km/h, was observed in B. subtilis 100-fold reduction, followed by B. seohaeanensis, B. cereus, B. vallismortis, with 90, 85, 80-folds reduction, respectively. Results indicate that the diversity of Bacillus sp. offers the potential ability for adaptation to harsh and untapped environments, also showed that the use of MICP on the soil surface can have a very significant role in reducing soil losses due to wind erosion.