Concrete biocalcification with carbonic anhydrase produced by a Novel bacterium Alcaligene faecalis G (Mn847723.1) isolated from concrete construction site

Abstract

Concrete is a composite material used for building constructions and is primarily a mixture of cement, water, coarse and fine aggregates. The aim of this research was to biocalcify concretes using carbonic anhydrase produced by bacteria isolated from concrete construction sites. Soil sample was obtained from a construction site in Bosso metropolis, Minna, Nigeria. It was serially diluted and plated on nutrient agar supplemented with calcium carbonate. The isolates obtained were screened for their ability to produce carbonic anhydrase using para-nitrophenyl acetate and the enzyme activities were determined. The isolate with carbonic anhydrase production potential was identified based on its cultural, biochemical and molecular characteristics. The carbonic anhydrase was used as mixing medium in the production of M25 Grade concrete cubes of 150 mm3 internal dimension and cured by open air, water sprinkling and water immersion methods. Compressive strength test was performed on the concretes after 7th, 14th and 28th days of curing. Scanning electron microscopy was used to determine the effects of carbonic anhydrase on the concretes and study the mechanism of calcification by the isolate. Two bacteria (GAA and GAB) were isolated from the soil samples and both showed positive reactions to screening with enzyme activities of 0.0321 and 0.0351 mmoles/ml-1 /secs-1 for isolates GAA and GAB respectively. Isolate GAB was identified as Alcaligenes faecalis subsp. parafaecalis strain G (MN847723.1). The results showed an increase in compressive strength of 11.54, 15.52 and 22.28 N/mm2 for 7, 14 and 28 days respectively. The scanning electron micrographs revealed distinctly visible precipitates of calcium carbonate crystals on the surfaces of the concrete treated with the carbonic anhydrase. The results obtained in the study showed that carbonic anhydrase has the ability to calcify concretes and could have huge potential applications in the biocalcification and healing of concretes.