Abstract
Bartonellae are hemotropic bacteria, agents of emerging zoonoses. These bacteria are heme auxotroph Alphaproteobacteria which must import heme for supporting their growth, as they cannot synthesize it. Therefore, Bartonella genome encodes for a complete heme uptake system allowing the transportation of this compound across the outer membrane, the periplasm and the inner membranes. Heme has been proposed to be used as an iron source for Bartonella since these bacteria do not synthesize a complete system required for iron Fe3+uptake. Similarly to other bacteria which use heme as an iron source, Bartonellae must transport this compound into the cytoplasm and degrade it to allow the release of iron from the tetrapyrrole ring. For Bartonella, the gene cluster devoted to the synthesis of the complete heme uptake system also contains a gene encoding for a polypeptide that shares homologies with heme trafficking or degrading enzymes. Using complementation of an E. coli mutant strain impaired in heme degradation, we demonstrated that HemS from Bartonella henselae expressed in E. coli allows the release of iron from heme. Purified HemS from B. henselae binds heme and can degrade it in the presence of a suitable electron donor, ascorbate or NADPH-cytochrome P450 reductase. Knocking down the expression of HemS in B. henselae reduces its ability to face H2O2 induced oxidative stress.
Highlights
Bartonella species are well established as human pathogens responsible for several emerging zoonoses [1]
The use of heme as iron source requires its transportation through the outer membrane, the periplasm, and the inner membrane
Like Yersinia enterocolitica, the heme degrading activity was demonstrated, but the reaction products were not characterized. This was the case for HemS from Yersinia enterocolitica [21], ChuS from E. coli O157:H7 [46]
Summary
Bartonella species are well established as human pathogens responsible for several emerging zoonoses [1]. The erythrocytes invasion can be proposed to be a strategy for Bartonella species to get heme that is absolutely required for the growth of B. henselae. Analysis of the complete genomic sequences of B. quintana and B. henselae supports the absolute requirement for heme since these two Bartonella species do not contain genes encoding for heme biosynthesis [11]. Enzyme allowing the release of iron from protoporphyrin IX leaving ring intact was identified in Escherichia coli (E. coli) [24] Controversial data about this heme dechelatase activity were published recently [25].In this report, we investigated the function of HemS for B. henselae, using functional complementation, and partial biochemical characterization. The effect of hemS knock down was investigated in B. henselae
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