The Stenotrophomonas maltophilia MntR miniregulon includes novel extracytoplasmic components and affects replication in Acanthamoeba castellanii phagosomes

Abstract

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.