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Bartonella henselae is a zoonotic pathogen that possesses a flea-cat-flea transmission cycle and causes cat scratch disease in humans via cat scratches and bites. In order to establish infection, B. henselae must overcome oxidative stress damage produced by the mammalian host and arthropod vector. B. henselae encodes for putative Fe²⁺ and Mn²⁺ transporter SitABCD. In B. henselae, SitAB knockdown increases sensitivity to hydrogen peroxide. We consistently show that SitAB knockdown decreases the ability of B. henselae to survive in both human endothelial cells and cat fleas, thus demonstrating that the SitABCD transporter plays an important role during the B. henselae infection cycle., (Copyright © 2013 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.)

Cells have devised a variety of protection systems against the toxic effects of dioxygen. Dioxygenases are part of this defence mechanism. In Escherichia coli, the positive regulator HcaR, a member of the LysR family of regulators, controls expression of the neighbouring genes, hcaA1, hcaA2, hcaC, hcaB and hcaD, coding for the 3-phenylpropionate dioxygenase complex and 3-phenylpropionate-2',3'-dihydrodiol dehydrogenase, that oxidizes 3-phenylpropionate to 3-(2,3-dihydroxyphenyl) propionate. Differences between expression of hcaR and expression of its target, hcaA, suggest that HcaR is involved in control of other cellular processes or that other regulatory proteins modulate hcaA expression. Protein expression profiling was used to identify other HcaR targets. Two-dimensional gel electrophoresis was used to compare the proteomes of wild-type E. coli and strains in which hcaR was disrupted. Several polypeptides whose production was up- or downregulated in the hcaR mutant were involved in the oxidative stress response. Subsequent experiments demonstrated that hcaR disruption was involved in regulation of genes involved in the oxidative stress response. Modification of the stress response also occurred in an hcaA1A2CD mutant strain. Using gel retardation, the HcaR binding site was estimated to be located about -70 to -55 bp upstream of the hcaA transcription start site. The expression of hcaR was repressed in the absence of oxygen by the ArcA/ArcB two-component system.