Characterization of live, dead, starved, and heat-treated S. pasteurii cells: implications for biomineralization in construction materials
Recently, interest has focused on leveraging the ability of certain microorganisms to improve the performance of porous infrastructure materials by inducing biogenic calcium carbonate precipitation. This biomineralization shows promise in the remediation of cracks in concrete. One concern for biomineralization applications in cementitious materials is that harsh conditions, such as elevated temperature and pH and lack of nutrients, might hinder or prevent bacterial carbonate production in situ. In this study, the surface charge and urease activity of Sporosarcina pasteurii cells that were exposed to moderate heat (55 °C for 4 hours) or suspended in simulated cement paste pore solution (absence of nutrients coupled with pH 13.6) were compared to those of dead cells (killed by autoclaving) or untreated cells. The zeta potential of S. pasteurii cells, which was used to approximate surface charge, was minimally affected by the treatments employed in this study. However, urease activity was greatly influenced. Heat-treated cells exhibited a considerable reduction in urease activity compared to untreated cells, and autoclaved cells or cells suspended in simulated pore solution for 1 day or longer did not exhibit any urease activity. Calcite content in bacterial cement pastes (i.e., cement mixed with bacterial cultures that hydrolyzed urea to produce ammonia and carbonates) was substantially increased as compared to that in neat paste. The results of this study suggest that urea hydrolysis (and concomitant production of carbonates) might be impaired or halted under environmental conditions that occur in cement pastes. However, bacterial surface charge can persist under these conditions, and the bacteria could be important for nucleation of calcium carbonate.