BIOCALCIFICATION OF CONCRETE USING CARBONIC ANYHDRASE PRODUCED BY SOIL BACTERIAL ISOLATES

ABSTRACT

Two (2) bacterial isolates obtained from Garima construction sites were named GARIMA (A) and (B), and code-named GA (A) and GA (B) respectively. They were screened for their carbonic anhydrase (CA) producing ability. Isolates GA (A) and GA (B) showed positive reaction to para-nitrophenylacetate (pNPA), producing yellow and peach/orange coloured colonies respectively. The isolates were used to produce the crude CA and the mean enzyme activity with standard error of mean for the CA from isolates GA (A) and GA (B) were 0.0321±0.0012 and 0.0351±0.0002 mmoles/mL-1 /sec-1 respectively, the GA (B) was subsequently used for the large scale production of the crude CA. Isolate GA (B) was identified as Alcaligenes faecalis subsp. parafaecalis strain G, using cultural, biochemical and molecular characterizations. Optimum substrate concentration for the CA from isolate GA (A) was 5 mM, with 50oC optimum temperature and an optimum pH of 8.5. While CA from A. faecalis subsp. parafaecalis Strain G had an optimum substrate concentration of 7 mM, optimum temperature of 50oC, and optimum pH of 9.5. The crude CA extract was used to reinforce concrete; the results showed an increase in crushing strength on days 7, 14 and 28 with mean crushing strength values of 11.54, 15.52 and 22.28 N/mm2 respectively, and with a percentage strength gain of 48.29%. The scanning electron micrographs revealed distinctly visible precipitates of calcium carbonate crystals on the surfaces of the concrete treated with the crude CA. These results indicate that CA could have huge potential applications in the bio-calcification and healing of concrete

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