The iron-binding siderophore enterobactin is required for the response of multi-drug resistant Klebsiella pneumoniae to zinc limitation.

UNLABELLED: To persist during infection Klebsiella pneumoniae must overcome nutrient iron and zinc limitation imposed by the host immune system through a process called nutritional immunity. Secreted small molecule siderophores are a major virulence determinant of Klebsiella pneumoniae pathogenesis and are presumed to overcome nutritional immunity by binding iron for bacterial acquisition. In this work, we set out to identify how a multi-drug resistant K. pneumoniae grows in zinc limited environments. Using unbiased transcriptomics, proteomics, and an arrayed transposon screen, we identified that synthesis and uptake of the siderophore enterobactin is required to allow for growth in low zinc conditions. Iron-specific chelators did not replicate this phenotype and addition of supplemental iron through heme in growth media could not complement severe growth defects of enterobactin mutant K. pneumoniae experiencing zinc limitation. Finally, zinc starvation induced enterobactin production independent of the canonical zinc uptake regulator (Zur) transcription factor suggesting an unidentified regulatory mechanism by which Gram-negative pathogens may respond to zinc stress. Together, these studies expand the role of enterobactin beyond iron regulation and highlight a previously unreported link between iron and zinc homeostasis in Klebsiella pneumoniae .

IMPORTANCE: Enterobactin is the archetypal model for understanding siderophore-mediated iron acquisition in Gram-negative bacteria and has the highest affinity for iron of any known molecule. Here, we identify an essential biological role for enterobactin acquisition in response to nutrient zinc limitation in an ST258 strain of Klebsiella pneumoniae and identify the enterobactin biosynthetic gene cluster as a Zur-independent locus of regulation to bacterial zinc stress. These findings expand the role of enterobactin in nutritional immunity and identify a new regulatory mechanism for Klebsiella pneumoniae zinc homeostasis.