Sporosarcina pasteurii urease gene expression regulation mechanism overcomes urease inhibition by hydrocarbons.

Hydrocarbons have been shown to both inhibit and enhance soil bacterial ureolysis. This suggests that indigenous ureolytic communities may perform better in the presence of contaminants than in their absence, pointing to an unresolved adaptation mechanism. In this study we conducted a molecular investigation on ureC gene expression of model Microbial-Induced Calcite Precipitation (MICP) bacterium Sporosarcina pasteurii during growth under increasing concentrations of hydrocarbon water extracts obtained from a coal tar polluted soil to ensure environmental relevance. Results indicated S. pasteurii ability to carry out ureolysis from low initial cell concentration (OD600, initial = 0.01). Flow cytometry showed insignificant differences in growth despite undergoing significant cell membrane damage at the highest hydrocarbon concentration. Quantification of ureC gene revealed a significant increase in urease transcription per unit cell with increasing hydrocarbon concentration, indicating higher urease synthesis to maintain similar ureolysis rates. We postulate this adaptation mechanism was in response to the nitrogen deficiency caused by intracellular urease inhibition by hydrocarbons. The temporal dynamics in ureC gene expression indicated urease transcription in S. pasteurii was inductive rather than constitutive. This gene up-regulation mechanism resulted in earlier ureolysis and achievement of environmental conditions favourable for calcium carbonate precipitation compared to the absence of hydrocarbons. The results of this study could reveal the underlying mechanism leading to enhanced soil ureolysis observed under certain hydrocarbon pollution scenarios.