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

Manganese homeostasis is crucial for bacterial survival, particularly for opportunistic pathogens like Stenotrophomonas maltophilia that switch lifestyles between contrasting environments. This study elucidates the manganese homeostasis system in S. maltophilia strain Sm18, a Mexican environmental isolate, revealing a sophisticated network that includes both conserved and novel components. We focus on the MntR miniregulon, which comprises the well-known inner-membrane importer MntH and exporter MntP, regulated by the Mn2+-responsive MntR metalloregulator. However, it also contains a TonB-dependent receptor (TBDR) with a distinctive CQNC motif likely involved in Mn2+ coordination and a periplasmic thioredoxin-fold protein (TFP). Both are coexpressed from a bicistronic operon under severe manganese and iron limitation and belong to novel families with a limited phyletic distribution. Transcriptomic profiling under varying manganese and iron concentrations revealed a tight interplay between these metals, emphasizing the ferrophilic nature of S. maltophilia and the differential expression of the MntR miniregulon core members. Additional transporters of the RND and CDF families were also modulated under dual metal limitation. Mutant analysis demonstrated that MntP is critical for survival, even at Mn levels that do not affect growth kinetics. MntH is required for optimal intracellular replication within Acanthamoeba castellanii phagosomes, highlighting its role in overcoming nutritional immunity. Our findings offer new insights into the remarkable adaptability of S. maltophilia to diverse environments, which contributes to its success as an opportunistic pathogen.