Quantitative proteomics of iron limitation in Klebsiella pneumoniae

Nutrient adaptation is key in limiting environments for the promotion of microbial growth and survival. In microbial systems, iron is an essential component for many cellular processes and bioavailability varies greatly among different conditions. In the bacterium, Klebsiella pneumoniae, the impact of iron limitation is known to alter transcriptional expression of iron-acquisition pathways and influences the secretion of iron-binding siderophores; however, a comprehensive view of iron limitation at the protein-level remains to be defined. Here, we apply a mass spectrometry-based quantitative proteomics strategy to profile the global impact of iron limitation on the cellular proteome and extracellular environment (secretome) of K. pneumoniae. Our data defines the impact of iron on proteins involved in transcriptional regulation and emphasizes the modulation of a vast array of proteins associated with iron acquisition, transport, and binding. We also identify proteins in the extracellular environment associated with conventional and nonconventional modes of secretion, as well as vesicle release. In particular, we demonstrate a new role for Lon protease in promoting iron homeostasis outside of the cell. Our characterization of Lon protease in K. pneumoniae validates roles in bacterial growth, cell division, iron utilization, and virulence. Moreover, our results uncover novel degradation candidates of Lon protease. Overall, we provide evidence of novel connections between Lon and iron in a bacterial system and define a unique role for Lon protease in the extracellular environment during nutrient limitation.