Endogenously produced H 2 O 2 is intimately involved in iron metabolism in Streptococcus pneumoniae
ABSTRACT
In the presence of molecular oxygen, the human pathogen Streptococcus pneumoniae produces and secretes large amounts of hydrogen peroxide (H 2 O 2 ), which can readily interact with free and heme-bound iron. Here, we investigated the role of the endogenously produced H 2 O 2 in iron acquisition. The data revealed that S. pneumoniae uses H 2 O 2 to liberate iron from met-hemoglobin (Hb-Fe 3+ ) extracellularly, allowing the bacterium to import and grow on free iron even when cultivated on met-hemoglobin as the only iron source. The loss of H 2 O 2 production leads to a dramatic pneumococcal intake of heme and is associated with a robust upregulation of most iron uptake machinery (indicating an iron starvation signal). These and other data reveal a close and previously unexplored relation between H 2 O 2 production and iron metabolism in S. pneumoniae . The data also show that, in addition to extracellular degradation, pneumococci are armed with H 2 O 2 -independent mechanisms for intracellular heme catabolism.
IMPORTANCE
Heme degradation provides pathogens with growth essential iron, leveraging on the host heme reservoir. Bacteria typically import and degrade heme enzymatically, and here, we demonstrated a significant deviation from this dogma. We found that Streptococcus pneumoniae liberates iron from met-hemoglobin extracellularly, in a hydrogen peroxide (H 2 O 2 )- and cell-dependent manner; this activity serves as a major iron acquisition mechanism for S. pneumoniae . Inhabiting oxygen-rich environments is a major part of pneumococcal biology, and hence, H 2 O 2 -mediated heme degradation likely supplies iron during infection. Moreover, H 2 O 2 reaction with ferrous hemoglobin but not with met-hemoglobin is known to result in heme breakdown. Therefore, the ability of pneumococci to degrade heme from met-hemoglobin is a new paradigm. Lastly, this study will inform other research as it demonstrates that extracellular degradation must be considered in the interpretations of experiments in which H 2 O 2 -producing bacteria are given heme or hemoproteins as an iron source.
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