A Putative Multicopper Oxidase Encoded by BAB2_0534 Promotes Melanin-Like Pigment Production and Intracellular Adaptation in Brucella abortus

Brucella abortus is an intracellular pathogen that must withstand oxidative stress and other hostile conditions encountered within host cells. Here, we investigated the contribution of BAB2_0534, a gene encoding a putative multicopper oxidase, to bacterial adaptation and persistence. Deletion of BAB2_0534 impaired pigment production in the presence of the melanin precursors L-DOPA and homogentisic acid, supporting a role for BAB2_0534 in phenolic substrate oxidation and melanin-like pigment biosynthesis. The mutant also exhibited increased susceptibility to oxidative stress and reduced survival with macrophages, indicating that BAB2_0534 contribute to intracellular adaptation. In vivo, mice infected with the ΔBAB2_0534 mutant showed significantly reduced splenic bacterial burdens compared with animals infected with the wild-type or complemented strains, demonstrating impaired persistence during infection. Consistently, Fontana–Masson-positive pigment was detected in tissues from wild-type-infected animals but was markedly reduced following infection with the mutant. Collectively, these findings support a model in which BAB2_0534-associated multicopper oxidase activity and pigment production contribute to oxidative stress resistance and intracellular persistence of B. abortus. This study characterizes BAB2_0534 as a previously unrecognized component of the adaptive mechanisms underlying Brucella persistence.