Cadmium-induced stress memory regulates Bacillus subtilis transport in porous media: Evidence from multi-scale...

Accurately predicting microbial transport under environmental stress in subsurface and aquatic environments is essential for assessing microbial risks, from modeling pathogen spread to optimizing in-situ bioremediation. While the biological foundations of microbial heavy metal tolerance are established, the effects of toxic heavy metals like cadmium (Cd) on microbial-mineral interactions and subsequent transport mechanisms remain poorly understood. To address these challenges, we explored how Cd stress reconfigures the deposition behavior of Bacillus subtilis in porous media. We report, for the first time, that Cd pre-exposure induces a "stress memory" that attenuates the acute escape response from toxic surfaces, thereby enhancing deposition. We employed a multi-scale approach, integrating column experiments, quartz crystal microbalance with dissipation (QCM-D), whole-genome resequencing, and proteomics. This integrated analysis determined that the history-dependent shift from active avoidance to tolerant colonization may be driven by enhanced EPS secretion (Increased by 100.0-139.0%) and a reprogrammed signal transduction pathway (increased from 0 to 5). Consequently, B. subtilis subjected to higher prior Cd stress exhibited more attenuated migration responses, resulting in greater deposition and colonization while encountering Cd on the contact surface, with maximum deposited mass being 49.1-91.2% higher than that of the unstressed cells. These findings highlight the necessity of incorporating microbial active behavior and stress adaptation strategies into existing transport theory and provide insights for the prevention and control of pathogenic bacteria in polluted environments.