Manganese homeostasis drives the Stenotrophomonas maltophilia oxidative stress defense and replication in Acanthamoeba castellanii phagosomes

Manganese homeostasis is essential for the environmental adaptability and pathogenic potential of Stenotrophomonas maltophilia, a bacterium that thrives across diverse and fluctuating niches. Here, we characterize the manganese homeostasis network of S. maltophilia strain Sm18, revealing a coordinated system that integrates conserved transporters with previously unrecognized components. Central to this system is an MntR-controlled miniregulon that includes the canonical Mn{superscript 2} importer MntH and exporter MntP, together with a TonB-dependent receptor (TBDR) and a periplasmic thioredoxin-fold protein (pTFP), both defining novel protein families with restricted phylogenetic distribution. Transcriptomic analyses under varying Mn{superscript 2} and Fe{superscript 2} conditions uncovered a tight interplay between these metals, highlighting the ferrophilic nature of S. maltophilia and the differential regulation of miniregulon components. Notably, the TBDR-pTFP module is strongly induced under combined Mn2+ and Fe2+ limitation, suggesting a specialized role in metal acquisition under nutrient-restricted conditions. Functional analyses demonstrated that MntP is required to prevent Mn toxicity even at sub-inhibitory concentrations, whereas MntH supports growth under oxidative stress and promotes intracellular replication within Acanthamoeba castellanii phagosomes. Together, these findings define a previously unrecognized Mn-responsive module that expands the MntR regulatory network and provides new insight into the mechanisms that enable S. maltophilia to adapt to metal-limited and host-associated environments.