89 Received : 05 July 2021, Revised : 14 March 2022 Accepted : 22 March 2022, Online published : 20 June 2022 Defence Life Science Journal, Vol. 7, No. 2, April 2022, pp. 89-96 DOI : 10.14429/dlsj.7.17279  2022, DESIDOC Isolation and Characterisation of Urease Producing Bacteria and their Capacity to Precipitate Calcium Carbonate Devang Bharatkumar Khambholja #* , Dharmishtha Gamit # , Hitesh Patel $ and Prashant Kumar & # Postgraduate Department of Medical Technology, B.N. Patel Institute of Paramedical and Science, Anand – 388 001, India $ Department of Biochemistry, Shri A.N. Patel PG Institute of Science and Research, Anand – 388 001, India & Ingress Bio-Solutions Pvt. Ltd., Ahmedabad – 382 470, India *Email: devangkhambholja@yahoo.in ABSTRACT The current study was designed to isolate and characterize urease-producing bacteria and to assess their ability to precipitate calcium carbonate. Total eight bacteria were isolated from dung-rich soil samples collected from Dakor, Gujarat. Out of these, two bacterial strains designated as DGDK-3 and DGDK-4 were found to produce a considerable level of urease in the initial screening on the urea agar medium. Based on morphological and physiological tests and more specifically by 16S rRNA gene sequencing analysis, these bacteria were identified as Quasibacillus sp. Strain DGDK-3 and Bacillus sp. Strain DGDK-4. The strains DGDK-3 and DGDK-4 showed 25 IU/ml and 89 IU/ ml urease activity, respectively. Also, the efficacy of both strains was tested for calcium carbonate precipitation. Results showed that both the isolates were competent to precipitate a significant level of calcium carbonate. The current work demonstrated that urease-producing bacteria can be utilised in bio-cementationas a crack sealing agent and as a natural stabilizing agent. Keywords: Urease; Calcite; Quasibacillussp; Dunghills 1. INTRODUCTION Urease is a nickel-dependent metallo enzyme that catalyzes the hydrolysis of urea to yield ammonia and carbamate. The carbamate is subsequently degraded by spontaneous hydrolysis to produce carbonate and another molecule of ammonia 1 . Functionally, ureases belong to the super family of amidohydrolases and phosphotriesterases. It was the first enzyme that was crystallised in the year 1926 from jack bean 2 . Urease is a cytosolic enzyme found in bacteria, fungi, higher plants, and several invertebrates, but not in animals 2-8 . From a clinical perspective, microbial urease has been extensively studied for its role in virulence factors that cause peptic ulceration, arthritis, urinary stones, and pyelonephritis 1,9 . Despite its negative reputation, microbial urease has extensive applications in clinical diagnosis, biotechnology, construction and agriculture 10-12 . Immobilised urease-based nanoparticles can be used as a biosensor tool for the detection of urea and other target compounds 10 . In fermented alcoholic beverages (red wine, Chinese wine, and white wine) production, microbial urease has been extensively used to remove urea which leads to the production of ethyl carbonate 13-14 . Recently, microbial-induced carbonate precipitation (MICP) using bacterial urease is a promising technique in the field of civil and geotechnical engineering. To reduce the environmental problem, in recent years MICP techniques have been developed as an alternative method for ground improvement 15-16 . Urease-producing bacteria such as Micrococcus yannanensis, Lysinibacillus Sp 15 , Sporosarcina pasteurii 17 and Bacillus megaterium 18 , have been reported as potential players for land improvement and calcium carbonate (calcite) precipitation. The calcite precipitation induced by Bacillus megaterium BSKAU, Bacillus licheniformis BSKNAU, Bacillus flexus BSKNAU 19 , Bacillus sphaericus and Bacillus pasteruii was reported to be effective in healing the cracks of concrete and increased its compressive strength 20-21 . A large number of bacteria have been reported to produce a significant level of urease 4 . In the majority of studies, the sample used for the bacterial isolation was soil 19,22 . Limited literature was available on the isolation of urease-producing bacteria from dunghills or dung-rich soil, as animal dung is the richest source of substrate urea. Hence, the possibility of urease producers is also extremely high. Therefore, the current study was designed to isolate and identification of urease-producing microaerobic bacteria and to evaluate their ability to precipitate calcium carbonate.