Abstract

Although microbially induced calcium carbonate precipita-tion (MICP) through ureolysis has been widely studied in en-vironmental engineering fields, urea utilization might cause environmental problems as a result of ammonia and nitrate production. In this study, many non-ureolytic calcium car-bonate-precipitating bacteria that induced an alkaline envi-ronment were isolated from the rhizosphere of Miscanthus sacchariflorus near an artificial stream and their ability to pre-cipitate calcium carbonate minerals with the absence of urea was investigated. MICP was observed using a phase-contrast microscope and ion-selective electrode. Only Lysinibacillus sp. YS11 showed MICP in aerobic conditions. Energy disper-sive X-ray spectrometry and X-ray diffraction confirmed the presence of calcium carbonate. Field emission scanning elec-tron microscopy analysis indicated the formation of morpho-logically distinct minerals around cells under these condi-tions. Monitoring of bacterial growth, pH changes, and Ca2+ concentrations under aerobic, hypoxia, and anaerobic con-ditions suggested that strain YS11 could induce alkaline con-ditions up to a pH of 8.9 and utilize 95% of free Ca2+ only under aerobic conditions. Unusual Ca2+ binding and its re-lease from cells were observed under hypoxia conditions. Bio-film and extracellular polymeric substances (EPS) formation were enhanced during MICP. Strain YS11 has resistance at high pH and in high salt concentrations, as well as its spore- forming ability, which supports its potential application for self-healing concrete.

• Keywords: Lysinibacillus sp. YS11; MICP; aeration; urea; aerobic MICP; X-ray diffraction