Abstract
BackgroundMicrobial organisms encounter a variety of environmental conditions, including changes to metal ion availability. Metal ions play an important role in many biological processes for growth and survival. As such, microbes alter their cellular protein levels and secretion patterns in adaptation to a changing environment. This study focuses on Klebsiella pneumoniae, an opportunistic bacterium responsible for nosocomial infections. By using K. pneumoniae, we aim to determine how a nutrient-limited environment (e.g., zinc depletion) modulates the cellular proteome and secretome of the bacterium. By testing virulence in vitro, we provide novel insight into bacterial responses to limited environments in the presence of the host.ResultsAnalysis of intra- and extracellular changes identified 2380 proteins from the total cellular proteome (cell pellet) and 246 secreted proteins (supernatant). Specifically, HutC, a repressor of the histidine utilization operon, showed significantly increased abundance under zinc-replete conditions, which coincided with an expected reduction in expression of genes within the hut operon from our validating qRT-PCR analysis. Additionally, we characterized a putative cation transport regulator, ChaB that showed significantly higher abundance under zinc-replete vs. -limited conditions, suggesting a role in metal ion homeostasis. Phenotypic analysis of a chaB deletion strain demonstrated a reduction in capsule production, zinc-dependent growth and ion utilization, and reduced virulence when compared to the wild-type strain.ConclusionsThis is first study to comprehensively profile the impact of zinc availability on the proteome and secretome of K. pneumoniae and uncover a novel connection between zinc transport and capsule production in the bacterial system.
Highlights
Microbial organisms encounter a variety of environmental conditions, including changes to metal ion availability
The present study aims to define how K. pneumoniae responds to a host-like setting by characterizing the relationship between zinc availability and intra- and extracellular bacterial processes via quantitative proteomics
We evaluate the impact of zinc availability by quantitative proteomic profiling of K. pneumoniae WT cells grown in zinc-limited (0 μM) and -replete (10 μM) media (Fig. 1)
Summary
Microbial organisms encounter a variety of environmental conditions, including changes to metal ion availability. Klebsiella pneumoniae is an opportunistic, Gramnegative bacterium that primarily causes nosocomial infections It is found ubiquitously in the environment, commonly in soil and surface water, but is very prevalent in medical settings [1]. Transition metals play a crucial role in numerous functions within all living organisms Their acquisition is essential to microbial survival, but the maintenance of intracellular concentration is of equal importance. Previous studies investigating the relationship between K. pneumoniae and transition metal availability focused primarily on iron limitation. These studies found an iron-associated impact on bacterial growth, capsule development, and protease secretion [7,8,9]. K. pneumoniae produces siderophores, iron-chelating molecules that can acquire free iron from the environment or sequester it from host proteins, to regulate intracellular iron levels during infection [10,11,12]
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