The use of organic additives to improve microbial-induced carbonate precipitation (MICP) is a novel and innovative idea. This study is the first to address the effects of the cationic biopolymer polylysine (poly-Lys) on CaCO3 crystallization and sand solidification by MICP. CaCO3 was precipitated with and without poly-Lys by hydrolysis of urea by using ureolytic bacteria, Pararhodobacter sp., in the presence of CaCl2 under different experimental conditions. The morphologies and polymorphs of the oven-dried precipitates were investigated using scanning electron microscopy and X-ray diffraction. A larger amount of precipitate was obtained with poly-Lys than with the conventional MICP method. The curve for the relationship between the poly-Lys concentration and amount of precipitate was bell shaped. In the presence of poly-Lys, the morphology changed from rhombohedral crystals to twin spherical crystals. The effects of poly-Lys on sand solidification were also investigated by syringe solidification at different bacterial injection intervals with and without poly-Lys. The addition of poly-Lys gave strongly cemented sand specimens that were stronger than those obtained by the conventional method. The results confirm that poly-Lys addition is an effective and sustainable way to improve the MICP efficiency and production of green materials for engineering applications.

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Biomineralization is a process of mineral formation in living organisms. Compared with nonbiogenic minerals, biominerals can be defined as organic−inorganic hybrid materials that have excellent physical and optical properties. In the current study, an artificial protein mimicking the outer shell of crayfish, composed of CaCO 3 , chitin, and proteins, was developed to facilitate organic−inorganic hybrid material formation by precipitation of calcium carbonate on the chitin matrix. The fusion protein (CaBP-ChBD) was constructed by introducing a shortsequence calcite-binding peptide (CaBP) into the chitin-binding domain (ChBD). Calcium carbonate precipitation experiments by enzymatic urea hydrolysis revealed that a significant increase in the CaCO 3 formation was achieved by adding CaBP-ChBD. Also, CaCO 3 was efficiently deposited on chitin particles decorated with CaBP-ChBD. Most interestingly, CaBP-ChBD would improve the performance in sand solidification more efficiently and sustainably in the process of biocementation technique. The developed recombinant protein could be used for the sustainable production of organic−inorganic green materials for engineering applications.

Microbially induced carbonate precipitation (MICP) by using ureolytic bacteria is a novel and environmentally friendly way to treat the un-cemented sand. It was implemented successfully in number of geotechnical applications. Use of organic additives to improve the MICP process is a novel and interesting approach. In this research, effect of the cationic biopolymer poly-l-lysine on the MICP process was investigated by using ureolytic bacteria Pararhodobacter sp. Urea hydrolysis by the bacteria in the presence of CaCl2 was conducted with the addition of the polymer under different conditions. Morphology of the precipitate of CaCO 3 after oven dried was analyzed by using the scanning electron microscope. Bell-shaped curve was obtained for the variation between the amount of the precipitate with the increase of the amount of the poly-l-lysine. Poly-Llysine gives higher amount of precipitate than conventional MICP process and morphology of the crystals changed drastically from well-developed rhombohedral crystals to ellipsoidal shaped aggregates.

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