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

Manganese homeostasis is crucial for opportunistic pathogens such as Stenotrophomonas maltophilia , which switch lifestyles between contrasting environments. This study elucidated the manganese homeostasis system in S. maltophilia strain Sm18, a Mexican environmental isolate, revealing a sophisticated network that includes conserved and novel components. We focused on the MntR miniregulon, which comprises the well-known inner membrane importer MntH and exporter MntP, both regulated by the Mn ²⁺ -responsive MntR metalloregulator. However, it also contains a TonB-dependent receptor (TBDR) with a distinctive CQNC motif likely involved in Mn ²⁺ coordination and a periplasmic thioredoxin-fold protein (pTFP). Both are co-expressed from a bicistronic operon under severe manganese and iron limitations and belong to novel families with a limited phyletic distribution. Transcriptomic profiling under varying Mn and Fe concentrations revealed a tight interplay between these metals, emphasizing the ferrophilic nature of S. maltophilia and the differential expression of MntR regulon core members. Additional transporters of the RND and CDF families were 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 growth under oxidative stress and intracellular replication within Acanthamoeba castellanii phagosomes, highlighting its role in overcoming nutritional immunity. Our findings provide new insights into the remarkable adaptability of S. maltophilia to diverse environments, contributing to its success as an opportunistic pathogen causing a broad range of infections in humans.