Commensal bacteria serve as an important line of defense against colonisation by opportunisitic pathogens, but the underlying molecular mechanisms remain poorly explored. Here, we show that strains of a commensal bacterium, Haemophilus haemolyticus, make hemophilin, a heme-binding protein that inhibits growth of the opportunistic pathogen, non-typeable Haemophilus influenzae (NTHi) in culture. We purified the NTHi-inhibitory protein from H. haemolyticus and identified the hemophilin gene using proteomics and a gene knockout. An x-ray crystal structure of recombinant hemophilin shows that the protein does not belong to any of the known heme-binding protein folds, suggesting that it evolved independently. Biochemical characterisation shows that heme can be captured in the ferrous or ferric state, and with a variety of small heme-ligands bound, suggesting that hemophilin could function under a range of physiological conditions. Hemophilin knockout bacteria show a limited capacity to utilise free heme for growth. Our data suggest that hemophilin is a hemophore and that inhibition of NTHi occurs by heme starvation, raising the possibility that competition from hemophilin-producing H. haemolyticus could antagonise NTHi colonisation in the respiratory tract.

Item Type:	Refereed Article
Keywords:	<i>Haemophilus haemolyticus</i>, hemophore, hemophilin, non-typeable <i>Haemophilus influenzae</i> (NTHi)
Research Division:	Biomedical and Clinical Sciences
Research Group:	Medical microbiology
Research Field:	Medical bacteriology
Objective Division:	Health
Objective Group:	Clinical health
Objective Field:	Clinical health not elsewhere classified
UTAS Author:	Latham, RD (Mr Roger Latham)
UTAS Author:	Atto, B (Miss Brianna Atto)
UTAS Author:	Wilson, R (Dr Richard Wilson)
UTAS Author:	Tristram, S (Dr Stephen Tristram)
UTAS Author:	Gell, DA (Dr David Gell)
ID Code:	136378
Year Published:	2019
Web of Science® Times Cited:	10
Deposited By:	Health Sciences
Deposited On:	2019-12-17
Last Modified:	2022-08-25
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