CHARACTERIZATION OF UREASE OF BACTERIAL ISOLATES FROM CEMENT FOR CONCRETE ENHANCEMENT

Abstract

Ureases are a group of enzymes that hydrolyse urea producing carbon dioxide and ammonia. Urease producing bacteria have shown their importance in microbially induced calcium carbonate precipitation in the construction industry. This study focused on the characterization of bacterial isolates from cement for concrete enhancement. Two (2) bacterial isolates assigned codes CA (B) and CA (F) were isolated from cement samples using enrichment culture technique. The isolates were screened for urease production and both tested positive. Enzyme activities of the two isolates were determined. Isolate CA (F) had the mean enzyme activity of 0.0005 mg/mM/s while isolate CA (B) had 0.0002 mg/mM/s. Optimum substrate concentration for urease activity of isolate CA (F) was 1mM while that of isolate CA (B) was at 3mM. The optimum temperature of urease activity for isolate CA (B) was 70℃, while isolate CA (F) had the optimum activity at 50℃. Optimum pH of both isolates was 9.5. Isolate CA (F) was identified as Lysinibacillus fusiformis strain 5B, using cultural, biochemical and molecular characterizations. It was used for large scale production of urease due to its higher enzyme activity. The urease produced was used in the production of bio-concretes. A control without urease was also cast. The cubes were cured for 7, 14 and 28 days and compressive strength of the cubes was determined. The compressive strength values of concrete calcified with urease on day 7, 14 and 28 were high with mean values of 24.71, 27.55 and 28.14 N/mm2 respectively. The control also had a high compressive strength of 20.46, 23.11 and 22.53 N/mm2 when compared to the International Standard comprehensive strengths for grade 25 concrete which are 16.25, 22.50 and 24.75 N/mm2. Scanning electron micrographs revealed visible precipitates of calcium carbonate crystals on the surface of concrete treated with urease, while the control had no visible crystals. The results of this study showed that urease produced by Lysinibacillus fusiformis strain 5B was able to enhance concrete strength.