Table of Contents

ABSTRACT

Ureases (urea amidohydrolases; EC 3.5.1.5) are nickel-dependent enzymes that catalyze the hydrolysis of urea into 2 mole of ammonia and 1 mole of carbon dioxide. Urease activity tends to increase the pH of surrounding environment as it produces ammonia, a basic molecule. These enzymes are widespread in nature, being synthesized by plants, fungi and bacteria, but not by animals. Plant and fungal ureases are hexamer of single type of ~90 kDa subunit with about 840 amino acids whereas, bacterial ureases are multimers of two or three polypeptide chains that correspond to the single chain of the plant/fungal urease. Urease from the bacterium Klebsiella aerogenes was the first to have its tridimensional structure solved by crystallography in the year 1995. Since then ureases from several bacterial strains have been studied. First application of urease enzyme was to detect Helicobacter pylori in stomach and it was restricted to be used as a diagnostic tool to detect the presence of pathogens in gastrointestinal or urinary tract as these pathogens produce urease. Later, Urease conductometric biosensors were innovated for detection of heavy-metal ions which consisted of interdigitated gold electrodes and enzyme membranes were used for a quantitative estimation of heavy-metal ions in polluted water. The most astonishing use of urease producing microbes is been made in the process called Microbially induced calcium carbonate precipitation (MICP). Under natural conditions, the precipitation of carbonates occurs very slowly over long geological times. In order to produce large amounts of carbonates rapidly, microbes could employ with the ability to create conditions for precipitation of carbonates in shorter times. Urea hydrolysis by ureolytic bacteria in presence CaCl2 aids this process by creating alkaline environment where high amounts of carbonates precipitate briefly describe this process. Bacterial strains that are been reported to achieve efficient carbonate precipitation are Bacillus pasteurii, Pseudomona ssp., Variovorax sp., Leuconostoc mesenteroides, Micrococcus sp., Bacillus subtilis, Deleya halophila, Halomonas eurihalina and Myxococcus xanthus. The use of MICP has gained importance due to its various applications that includes removal of heavy metals and radionucleotides, removal of calcium from wastewater and biodegradation of pollutants, atmospheric CO2 sequestration, remediation of building materials, in cement industry to produce self-healing cement preparations, sealing cracks restoration of monuments; preparing eco-friendly bricks where soil used is bio-calcified, modifying the properties of soil thus, bacterial carbonates produced by the action of urease are serving many interdisciplinary fields.

Keywords: self healing concrete, bioaugmentation, urolysis, calcium precipitation