Roles of SmeYZ, SbiAB, and SmeDEF Efflux Systems in Iron Homeostasis of Stenotrophomonas maltophilia

Abstract

Efflux pumps display high efficiency of drug extrusion, which underlies their roles in multidrug resistance. In addition, efflux pumps have physiological functions, and their expression is tightly regulated by various environmental and physiological signals.

The sbiTRS Operon Contributes to Stenobactin-Mediated Iron Utilization in Stenotrophomonas maltophilia

“…Stenobactin is the sole known siderophore in S. maltophilia ( 20 ). Some genes involved in stenobactin-mediated ferric iron acquisition have been revealed, including stenobactin synthesis genes ( entCEBB’FA ) ( 20 ), stenobactin secretion genes ( smeYZ , smeDEF , and sbiAB ) ( 21 ), and ferri-stenobactin uptake gene ( fepA ) ( 22 ). These genes’ expression in KJ and KJΔFur revealed by transcriptome analysis was summarized in Table 1 .…”

“…2A ). The proteins encoded by these five genes included a two-component regulatory system (Smlt2645-Smlt2646), an inner membrane protein (Smlt2644), and an ABC-type SbiAB efflux pump, which acts as an outlet for stenobactin secretion ( 21 ). Given this genomic organization, we designated Smlt2644, Smlt2645, and Smlt2646 as sbiT , sbiR , and sbiS , respectively.…”

“…5A and 5B ). Some of the genes involved in stenobactin-mediated ferric iron acquisition in S. maltophilia have been characterized, including stenobactin synthesis genes ( entCEBB’FA operon) ( 20 ), stenobactin secretion genes ( smeYZ , smeDEF , and SbiAB operons) ( 21 ), and ferri-stenobactin uptake TonB-dependent outer membrane receptor FepA ( 22 ). To assess whether these genes are members of the SbiSR TCS, we compared their expression levels in KJ, KJΔSbiT, KJΔSbiTRS, KJΔSbiR, KJΔSbiS, and KJΔSbiSR using qRT-PCR.…”

“…7B ). SmeDEF and SbiAB are efflux pumps used for stenobactin secretion ( 21 ). Although the genes involved in stenobactin synthesis and ferri-stenobactin uptake seem not to be the members of SbiSR TCS, we can expect them to be upregulated in a coordinated manner in response to iron depletion via other unidentified Fur-involved regulatory circuits, since these genes are the members of Fur regulon ( Table 1 ; Fig.…”

“…In response to iron depletion stress, S. maltophilia synthesizes the catechol-type siderophore stenobactin via the entCEBB’FA system ( 20 ). SmeYZ, SmeDEF, and SbiAB pumps are known outlets for stenobactin export into the extracellular environment ( 21 ). Once bound to ferric iron, ferri-stenobactin is taken up by the TonB-dependent outer membrane receptor FepA ( 22 ).…”