Identification of mechanisms involved in iron and haem uptake in Bartonella birtlesii: in silico and in vivo approaches

TonB Energy Transduction Systems of Riemerella anatipestifer Are Required for Iron and Hemin Utilization

Riemerella anatipestifer (R. anatipestifer) is one of the most important pathogens in ducks. The bacteria causes acute or chronic septicemia characterized by fibrinous pericarditis and meningitis. The R. anatipestifer genome encodes multiple iron/hemin-uptake systems that facilitate adaptation to iron-limited host environments. These systems include several TonB-dependent transporters and three TonB proteins responsible for energy transduction. These three tonB genes are present in all the R. anatipestifer genomes sequenced so far. Two of these genes are contained within the exbB-exbD-tonB1 and exbB-exbD-exbD-tonB2 operons. The third, tonB3, forms a monocistronic transcription unit. The inability to recover derivatives deleted for this gene suggests its product is essential for R. anatipestifer growth. Here, we show that deletion of tonB1 had no effect on hemin uptake of R. anatipestifer, though disruption of tonB2 strongly decreases hemin uptake, and disruption of both tonB1 and tonB2 abolishes the transport of exogenously added hemin. The ability of R. anatipestifer to grow on iron-depleted medium is decreased by tonB2 but not tonB1 disruption. When expressed in an E. coli model strain, the TonB1 complex, TonB2 complex, and TonB3 protein from R. anatipestifer cannot energize heterologous hemin transporters. Further, only the TonB1 complex can energize a R. anatipestifer hemin transporter when co-expressed in an E. coli model strain.

Heme binding proteins of Bartonella henselae are required when undergoing oxidative stress during cell and flea invasion

Bartonella are hemotropic bacteria responsible for emerging zoonoses. These heme auxotroph alphaproteobacteria must import heme for their growth, since they cannot synthesize it. To import exogenous heme, Bartonella genomes encode for a complete heme uptake system enabling transportation of this compound into the cytoplasm and degrading it to release iron. In addition, these bacteria encode for four or five outer membrane heme binding proteins (Hbps). The structural genes of these highly homologous proteins are expressed differently depending on oxygen, temperature and heme concentrations. These proteins were hypothesized as being involved in various cellular processes according to their ability to bind heme and their regulation profile. In this report, we investigated the roles of the four Hbps of Bartonella henselae, responsible for cat scratch disease. We show that Hbps can bind heme in vitro. They are able to enhance the efficiency of heme uptake when co-expressed with a heme transporter in Escherichia coli. Using B. henselae Hbp knockdown mutants, we show that these proteins are involved in defense against the oxidative stress, colonization of human endothelial cell and survival in the flea.