Revisiting the urease production of MICP-relevant bacterium Sporosarcina pasteurii during cultivation

Abstract

The ureolytic bacterium Sporosarcina pasteurii is commonly used for Microbial Induced Calcium Carbonate Precipitation (MICP). This process has a variety of applications in the fields of construction, geotechnical engineering, and environmental remediation. However, the factors influencing urease activity of S. pasteurii during cultivation are not yet fully understood. Even though there is debate over whether higher urease activity is in fact beneficial for MICP applications, knowledge about urease production can help provide ureolytic biomass more cost-effectively, reducing overall production costs. This study revisits the effect of various cultivation conditions on growth and urease activity by using an automated high-throughput microbioreactor system combined with a novel system for high-throughput urease activity quantification. This experimental set-up allows for unprecedented data density and enables new insights into urease production of S. pasteurii.Several factors were tested, including oxygen limitation, the feeding of urea, choice of ammonium salt, the proportion of ammonium salt in the medium, and lowering the pH during cultivation; none of these had a notable impact on urease production. Only the addition of a broad spectrum of nutrients through regular feeding with highly concentrated yeast extract and glucose led to a 70 % increased specific urease activity compared to a batch culture.These results can improve the understanding of the regulatory mechanisms governing urease expression in S. pasteurii during cultivation, and allow to adapt the cultivation process accordingly. Additionally, the new system for automated high-throughput enzyme activity determination presented in this study could be applied to optimize bioprocesses involving other ion producing enzymes.