Ferrochelatase is present in Brucella abortus and is critical for its intracellular survival and virulence

Brucella spp. are pathogenic bacteria that cause brucellosis, an animal dis ease which can also affect humans. Although understanding the pathogenesis is important for the health of animals and humans, little is known about vi rulence factors associated with it. In order for chronic disease to be esta blished, Brucella spp. have developed the ability to survive inside phagocy tes by evading cell defenses. It hides inside vacuoles, where it then repli cates, indicating that it has an active metabolism. The purpose of this wor k was to obtain better insight into the intracellular metabolism of Brucell a abortus. During a B. abortus genomic sequencing project, a clone coding a putative gene homologous to hemH was identified and sequenced. The amino a cid sequence revealed high homology to members of the ferrochelatase family . A knockout mutant displayed auxotrophy for hemin, defective intracellular survival inside J774 and HeLa cells, and lack of virulence in BALB/c mice. This phenotype was overcome by complementing the mutant strain with a plas mid harboring wild-type hemH. These data demonstrate that B. abortus synthe sizes its own heme and also has the ability to use an external source of he me; however, inside cells, there is not enough available heme to support it s intracellular metabolism. It is concluded that ferrochelatase is essentia l for the multiplication and intracellular survival of B. abortus and thus for the establishment of chronic disease as well.