Isolation of alkaliphilic calcifying bacteria and their feasibility for enhanced CaCO precipitation in bio-based cementitious composites.

Microbially induced calcite precipitation (MICP), secreted through biological metabolic activity, secured an imperative position in remedial measures within the construction industry subsequent to ecological, environmental and economical returns. However, this contemporary recurrent healing system is susceptible to microbial depletion in the highly alkaline cementitious environment. Therefore, researchers are probing for alkali resistant calcifying microbes. In the present study, alkaliphilic microbes were isolated from different soil sources and screened for probable CaCO precipitation. Non-ureolytic pathway (oxidation of organic carbon) was adopted for calcite precipitation to eliminate the production of toxic ammonia. For this purpose, calcium lactate Ca(C H O ) and calcium acetate Ca(CH COO) were used as CaCO precipitation precursors. The quantification protocol for precipitated CaCO was established to select potent microbial species for implementation in the alkaline cementitious systems as more than 50% of isolates were able to precipitate CaCO . Results suggested 80% of potent calcifying strains isolated in this study, portrayed higher calcite precipitation at pH 10 when compared to pH 7. Ten superlative morphologically distinct isolates capable of CaCO production were identified by 16SrRNA sequencing. Sequenced microbes were identified as species of Bacillus, Arthrobacter, Planococcus, Chryseomicrobium and Corynebacterium. Further, microstructure of precipitated CaCO was inspected through scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermal gravimetric (TG) analysis. Then, the selected microbes were investigated in the cementitious mortar to rule out any detrimental effects on mechanical properties. These strains showed maximum of 36% increase in compressive strength and 96% increase in flexural strength. Bacillus, Arthrobacter, Corynebacterium and Planococcus genera have been reported as CaCO producers but isolated strains have not yet been investigated in conjunction with cementitious mortar. Moreover, species of Chryseomicrobium and Glutamicibacter were reported first time as calcifying strains.