Recent studies have established Hypoxia inducible factor-1 (HIF-1) activation during bacterial infections. However, molecular details of how bacteria activate HIF-1 remain unclear. We could demonstrate earlier that the angiogenic bacterium Bartonella henselae activates HIF-1 in an oxygen-dependent manner. Now we pursued the role of bacterial siderophores in HIF-1 activation during infection with Enterobacteriaceae. In fact, orogastral infection of mice with Yersinia enterocolitica led to functional activation of HIF-1 in Peyers patches. As intestinal epithelial HIF-1 targeted mice showed higher susceptibility to orogastral Y. enterocolitica infections, bacterial HIF-1 activation appears to represent a host defense mechanism. Additional studies with Y. enterocolitica, Salmonella enterica subsp. enterica or Enterobacter aerogenes and, moreover, application of their siderophores (yersiniabactin, salmochelin, aerobactin) caused a robust HIF-1 response in human epithelia and endothelia, independent of cellular hypoxia. In contrast, HIF-1 activation was almost completely attenuated upon infection with siderophore-uptake deficient bacteria. Taken together, this study reveals what we believe to be a previously unrecognized role of bacterial siderophores for hypoxia-independent activation of HIF-1 during infections with bacteria. Currently, we investigate other bacterial mechanisms possibly involved in the activation of HIF-1.