Biofilm Transcriptome Highlights Adaptation to Starvation and General Stress while Maintaining Virulence
Résumé
Leptospira interrogans navigates a dual existence: surviving in environmental reservoirs and infecting mammalian hosts. Leptospira biofilm formation is posited as a crucial survival strategy in environmental contexts. Understanding the dynamics between biofilm lifestyle and pathogen virulence is therefore likely pivotal and has been hypothesized to be a key mechanism by which pathogenic Leptospira complete their life cycle. To further explore this survival strategy, our study focused on elucidating the biological state of pathogenic Leptospira within biofilms, particularly aiming at uncovering the adaptations and regulatory mechanisms that are involved in such complex microenvironments. In order to determine the transcriptional profile of pathogenic Leptospira in biofilm, we compared the genome-wide gene expression in a late biofilms (21 days old) with that in exponential planktonic cultures (5 days old), revealing a pronounced transcritpomic shift. while genes linked to motility, energy production, and metabolism were downregulated, those governing stress response, metal ion defense, and redox homeostasis showed a significant upsurge, hinting at a tailored defensive strategy against oxidative stress in late biofilms. A standout finding was the heightened expression of the csoR, copZ, and copA locus, integral to copper ion stress response in other bacterial genera, suggesting a unique adaptation to metal-induced stress. Despite a reduced metabolic state in biofilms, disruption swiftly restored metabolic activity. Crucially, bacteria either in mature biofilms or disrupted thereof retained virulence in a hamster infection model, defying the notion that biofilm maturation abolishes pathogenicity. In summary, our study illustrates Leptospira’s adaptive equilibrium in biofilms: minimizing cellular energy expenditure as a means to conserve resources, potentially aiding in withstanding stresses while maintaining its infectious edge. These insights are crucial for understanding the survival strategies of Leptospira, revealing that a biofilm lifestyle may confer an advantage in maintaining virulence. This understanding is vital for managing leptospirosis across both environmental reservoirs and mammalian hosts.