Native Bacterial Community Convergence in Augmented and Stimulated Ureolytic MICP Biocementation

Abstract

Microbially induced calcite precipitation is a biomineralization process with numerous civil engineering and ground improvement applications. In replicate soil columns, the efficacy and microbial composition of soil bioaugmented with the ureolytic bacterium Sporosarcina pasteurii were compared to a biostimulation method that enriches native ureolytic soil bacteria in situ under conditions analogous to field implementation. The selective enrichment resulting from sequential stimulation treatments strongly selected for Firmicutes (>97%), with Sporosarcina and Lysinibacillus comprising 60 to 94% of high-throughput 16S rDNA sequences in each suspended community sample. Seven species of the former and two of the latter were present in greater than 10% abundance at different times, demonstrating unexpected within-genus diversity and robustness in the suspended phase of this highly selective environment. Based on longer 16S sequences, it was inferred that augmented S. pasteurii competed poorly with natural bacteria, decreasing to below detection after nine treatments, while the native microbial community was enriched to approximately that present in the stimulated columns. These analyses were corroborated by the observed convergence in bulk ureolytic rates and calcite contents between techniques. However, a 10-fold discrepancy between the observed cell density and an activity-based estimate indicates the attached community, uncharacterized despite efforts, substantially contributes to bulk behavior.

Effect of cell density on decrease in hydraulic conductivity by microbial calcite precipitation

“…Therefore, the urease activity generated by cells in the columns would be exhausted probably because there was no nutrient source in the precipitation solution. Graddy et al ( 2021 ) investigated feeding Sporosarcina pasteurii in natural sands. The results indicated that native species of Sporosarcina quickly outcompeted feeding cells (Graddy et al 2021 ) most probably they are spore formers, and spores are difficult to kill even by autoclaving.…”

“…Graddy et al ( 2021 ) investigated feeding Sporosarcina pasteurii in natural sands. The results indicated that native species of Sporosarcina quickly outcompeted feeding cells (Graddy et al 2021 ) most probably they are spore formers, and spores are difficult to kill even by autoclaving.…”

Heavy metal bioremediation using microbially induced carbonate precipitation: Key factors and enhancement strategies

“…Biostimulation achieves MICP by stimulating the growth of native microorganisms with desirable metabolic capabilities using an enrichment and nutrient medium ( Gat et al, 2016 ). It is cost-effective and environmentally viable, since indigenous soil strains may have advantages in survivability and adaptability ( Graddy et al, 2021 ), making them compatible with the applied polluted environment ( Gat et al, 2016 ; Dhami et al, 2017 ; Graddy et al, 2018 ). For instance, the biostimulation process that applied to accelerate MICP in Cu immobilization also yielded favorable results; specifically, from 45.54 mg/kg, the exchangeable soluble fraction of Cu in soil fell to 1.55 mg/kg ( Chen and Achal, 2019 ).…”

Assessing Indigenous Soil Ureolytic Bacteria as Potential Agents for Soil Stabilization

“…Noteworthy, indigenous microorganisms distributed within the soil environment can be enriched in situ (bio-stimulation) by modifying local environmental conditions which favour the diversity and distribution of existing bacterial community with required urease capabilities for various MICP applications (Gowthaman et al 2019;Graddy et al 2021). Thus, it confirms the promising nature of utilizing indigenous urease-producing bacteria as agents for MICP applications.…”