Abstract
ABSTRACTSiderophores are small molecular iron chelators that are produced by microbes and whose most notable function is to sequester iron from the host and provide this essential metal nutrient to microbes. Recent studies have proposed additional, noncanonical roles for siderophores, including the acquisition of noniron metals and modulation of host functions. Recently, Holden et al. (V. I. Holden, P. Breen, S. Houle, C. M. Dozois, and M. A. Bachman, mBio 7:e01397-16, 2016, http://dx.doi.org/10.1128/mBio.01397-16) showed that siderophores secreted by Klebsiella pneumoniae during lung infection induce stabilization of the transcription factor HIF-1α, increase the expression of proinflammatory cytokines in the lung, and promote dissemination of K. pneumoniae to the spleen. Thus, their study demonstrated novel roles for siderophores in vivo, beyond iron sequestration. The interaction of siderophores with host cells further promotes the pathogenicity of K. pneumoniae and is likely relevant for other pathogens that also secrete siderophores in the host.
Highlights
Siderophores are small molecular iron chelators that are produced by microbes and whose most notable function is to sequester iron from the host and provide this essential metal nutrient to microbes
In the “tug of war” for iron, many enteric pathogens have acquired additional mechanisms to evade lipocalin-2 activity, in particular by producing and acquiring “stealth siderophores” that are not bound by lipocalin-2 [5]
Various combinations of siderophores are found among clinical isolates of Klebsiella pneumoniae [8], a member of the Enterobacteriaceae that causes pneumonia, urinary tract infection, and septicemia, largely in hospitalized patients. This diversity in siderophores impacts the replicative niche of K. pneumoniae in the host [8, 9] and suggests that siderophores contribute to pathogenesis via different mechanisms [10]
Summary
Siderophores are small molecular iron chelators that are produced by microbes and whose most notable function is to sequester iron from the host and provide this essential metal nutrient to microbes. Enterobactin ( known as enterochelin) is a catecholate siderophore produced by both commensal and pathogenic Enterobacteriaceae and has greater affinity for iron than host molecules, such as transferrin and lactoferrin [3]. The host has evolved to produce lipocalin-2 ( known as neutrophil gelatinase-associated lipocalin, siderocalin, and 24p3), an antimicrobial protein that binds to iron-laden enterobactin, thereby preventing its reuptake by bacteria [4].
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