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<p>Cement contaminated soils represent chemically extreme environments, characterized by high alkalinity and high ion concentrations, which selectively enrich microorganisms capable withstanding substantial physicochemical stress. In this study, alkaliphilic ureolytic bacteria were isolated from cement contaminated soil samples collected from construction sites using urea-supplemented nutrient agar at pH 9.0. The isolates were screened for their potential to have ureolytic and drive microbially induced calcium carbonate precipitation. This study, recovered 17 morphologically distinct bacterial isolates on the initial isolation, and six were selected based on strong urease activity and calcium carbonate precipitation capacity. Among the selected strains, five were Gram-positive, endospore-forming bacteria, while one was Gram-negative, non-spore forming bacterium. All strains exhibited ureolytic, alkaliphilic, salt tolerant, and moderately thermophilic characteristics. Urease activity varied considerably among strains, with isolate MHS3 showing the highest activity (7.91 mM urea hydrolyzed.min<sup>− 1</sup>), whereas isolate Y showed the lowest (3.93 mM urea hydrolyzed.ml<sup>− 1</sup>). 16&#xa0;S rRNA gene sequencing identified four isolates belonging to the genus <i>Bacillus</i> (<i>Bacillus sp.</i> MHS2, <i>B. subtilis</i> MHS3, <i>B. paramycoides</i> MHS4, <i>B. pumilus</i> B2), one genus <i>Lysinibacillus</i> (<i>L. boronitolerans</i> Y) and genus <i>Halomonas</i> (<i>Halomonas sp</i>. CSS4), all showing ≥ 98% similarity to known strains. All strains grewn in media containing ≥ 5% urea and up to 7% (w/v) NaCl, with optimal growth at 30–35&#xa0;°C and pH 8–9. They also managed to grown at increased temperature up to 45&#xa0;°C and pH 11.0, although viable cell density declined by 83.27% under these conditions. All isolates precipitated calcium carbonate, with <i>B. subtilis</i> (MHS3) producing the highest yield (8.04&#xa0;g L<sup>− 1</sup>) and <i>Halomonas</i> sp. (CSS4) the lowest (4.96&#xa0;g L<sup>− 1</sup>). FTIR, SEM and XRD analyses confirmed calcite and vaterite as the dominant calcium carbonate polymorphs in the precipitate produced These findings highlight the potential of alkaliphilic ureolytic bacteria from cement contaminated environments for applications in biocementation, soil stabilization and future bioremediation strategies.</p>

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Isolation and characterization of ureolytic bacteria driving microbially induced calcite precipitation in cement contaminated soil

  • 期刊论文

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  • 发表日期：

    2026年4月27日

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  • Daniel Mulu Mengistu,
  • Daniel Girma Hordofa

摘要

Cement contaminated soils represent chemically extreme environments, characterized by high alkalinity and high ion concentrations, which selectively enrich microorganisms capable withstanding substantial physicochemical stress. In this study, alkaliphilic ureolytic bacteria were isolated from cement contaminated soil samples collected from construction sites using urea-supplemented nutrient agar at pH 9.0. The isolates were screened for their potential to have ureolytic and drive microbially induced calcium carbonate precipitation. This study, recovered 17 morphologically distinct bacterial isolates on the initial isolation, and six were selected based on strong urease activity and calcium carbonate precipitation capacity. Among the selected strains, five were Gram-positive, endospore-forming bacteria, while one was Gram-negative, non-spore forming bacterium. All strains exhibited ureolytic, alkaliphilic, salt tolerant, and moderately thermophilic characteristics. Urease activity varied considerably among strains, with isolate MHS3 showing the highest activity (7.91 mM urea hydrolyzed.min− 1), whereas isolate Y showed the lowest (3.93 mM urea hydrolyzed.ml− 1). 16 S rRNA gene sequencing identified four isolates belonging to the genus Bacillus (Bacillus sp. MHS2, B. subtilis MHS3, B. paramycoides MHS4, B. pumilus B2), one genus Lysinibacillus (L. boronitolerans Y) and genus Halomonas (Halomonas sp. CSS4), all showing ≥ 98% similarity to known strains. All strains grewn in media containing ≥ 5% urea and up to 7% (w/v) NaCl, with optimal growth at 30–35 °C and pH 8–9. They also managed to grown at increased temperature up to 45 °C and pH 11.0, although viable cell density declined by 83.27% under these conditions. All isolates precipitated calcium carbonate, with B. subtilis (MHS3) producing the highest yield (8.04 g L− 1) and Halomonas sp. (CSS4) the lowest (4.96 g L− 1). FTIR, SEM and XRD analyses confirmed calcite and vaterite as the dominant calcium carbonate polymorphs in the precipitate produced These findings highlight the potential of alkaliphilic ureolytic bacteria from cement contaminated environments for applications in biocementation, soil stabilization and future bioremediation strategies.