The fciTABC and feoABI systems contribute to ferric citrate acquisition in Stenotrophomonas maltophilia

Abstract

AbstractBackgroundStenotrophomonas maltophilia, a member of γ-proteobacteria, is a ubiquitous environmental bacterium that is recognized as an opportunistic nosocomial pathogen. FecABCD system contributes to ferric citrate acquisition inEscherichia coli. FeoABC system, consisting of an inner membrane transporter (FeoB) and two cytoplasmic proteins (FeoA and FeoC), is a well-known ferrous iron transporter system in γ-proteobacteria. As revealed by the sequenced genome,S. maltophiliaappears to be equipped with several iron acquisition systems; however, the understanding of these systems is limited. In this study, we aimed to elucidate the ferric citrate acquisition system ofS. maltophilia.MethodsCandidate genes searching and function validation are the strategy for elucidating the genes involved in ferric citrate acquisition. The candidate genes responsible for ferric citrate acquisition were firstly selected using FecABCD ofE. colias a reference, and then revealed by transcriptome analysis ofS. maltophiliaKJ with and without 2,2′-dipyridyl (DIP) treatment. Function validation was carried out by deletion mutant construction and ferric citrate utilization assay. The bacterial adenylate cyclase two-hybrid system was used to verify intra-membrane protein–protein interaction.ResultsSmlt2858 and Smlt2356, the homologues of FecA and FecC/D ofE. coli, were first considered; however, deletion mutant construction and functional validation ruled out their involvement in ferric citrate acquisition.FciA(Smlt1148), revealed by its upregulation in DIP-treated KJ cells, was the outer membrane receptor for ferric citrate uptake. ThefciAgene is a member of thefciTABCoperon, in whichfciT, fciA,andfciCparticipated in ferric citrate acquisition. Uniquely, the Feo system ofS. maltophiliais composed of a cytoplasmic protein FeoA, an inner membrane transporter FeoB, and a predicted inner membrane protein FeoI. The intra-membrane protein–protein interaction between FeoB and FeoI may extend the substrate profile of FeoB to ferric citrate. FeoABI system functioned as an inner membrane transporter of ferric citrate.ConclusionsThe FciTABC and FeoABI systems contribute to ferric citrate acquisition inS. maltophilia.