Optimisation of carbonic anhydrase produced by soil isolates for biocalcification of concrete.

Abstract

Carbonic Anhydrase (CA) is a metalloenzyme containing zinc able to catalyse the reversible hydration reaction of CO2. This study aimed to optimize the production of carbonic anhydrase by bacteria isolated from soil collected from selected concrete construction sites in Minna, Nigeria. The soil samples were transported to the Microbiology Laboratory, Federal University of Technology, Minna. The soil samples were serially diluted ten-fold and screened for the presence of carbonic anhydrase producing bacteria using broth-peptone agar medium containing 60 g/L CaCO3. The medium was flooded with 10 mM solution of para-nitrophenyl acetate (pNPA), and observed for bacterial growth. Further screening was carried out by inoculating the bacteria in a culture medium composed of 1.8 g of pNPA and 25 mg of ampicillin at pH 7.0. Organisms isolated that gave positive reaction to the screening was identified as Bacillus sp. The organism was cultured on large scale, centrifuged at 7,000 rpm and sterilised by filtration. The resulting cell free supernatant (crude enzyme) was assayed for carbonic anhydrase activity. The enzyme produced was used for the production of concrete cubes according to the recommended specifications. Controls, without the enzyme were set for the experiment. The concretes were cured and subjected to split-tensile, compressive strength and water penetration tests. The results of this study showed that carbonic anhydrase was able to enhance the concrete as compared to the control, and therefore can be used for bio-calcification.