Zinc Homeostasis in Brucella ovis Under Zinc Scarcity: Characterization of the ZnuABC Zinc Import System and of a Newly Identified Gene of the Zur Regulon

Abstract

The zinc import system ZnuABC is essential for the virulence of smooth (bearing O-polysaccharide chains) zoonotic Brucella species but remains uncharacterized in the non-zoonotic rough (lacking O-chains) species Brucella ovis, the causative agent of a type of ovine brucellosis of veterinary and economic importance. In this study, we constructed a panel of B. ovis mutants for genes of the znuACB locus that were characterized by evaluating growth, gene expression, protein abundance, metal content, and virulence in mice. We identified a ZigA ortholog (uncharacterized in the genus Brucella but linked to zinc homeostasis and histidine metabolism in other bacteria) that belongs to the Zur regulon and is transcriptionally modulated in a zinc-dependent manner as the ZnuABC system. A potential link of B. ovis ZigA with histidine catabolism and a crosstalk between the homeostasis of zinc and other metals have been identified as areas for further exploration. Remarkably, the znuA, zigAznuA and znuACB mutants of B. ovis displayed wild-type virulence in mice, which contrasts with the reported attenuation for the znuA mutant of smooth zoonotic Brucella species sharing a high degree of DNA homology. These results significantly enlarge the knowledge about the metallobiology of the genus Brucella, providing new perspectives for related research.