Disruption of the Nitric Oxide Reductase Operon via norD Deletion Does Not Affect Brucella abortus 2308W Virulence

<i>Brucella</i> are intracellular pathogens that use flexible respiratory strategies to adapt to oxygen-limited conditions. The <i>nor</i> operon encodes components of nitric oxide reductase (Nor), which are involved in denitrification and nitric oxide (NO) detoxification. In this study, the role of the <i>norD</i> gene in nitrate-dependent respiration, resistance to nitrosative stress, and intracellular persistence in <i>B. abortus</i> was evaluated. A non-polar Δ<i>norD</i> mutant was generated in strain 2308W and its survival and growth under aerobic and anaerobic conditions, with and without nitrate, as well as its tolerance to NO donors, were analyzed. In addition, its behavior was evaluated in activated and non-activated murine RAW264.7 and human THP-1 macrophages and in a murine infection model. The deletion of <i>norD</i> did not affect viability or growth under any of the conditions tested, nor did it alter resistance to NO in vitro or within activated macrophages. Furthermore, the mutant showed virulence comparable to the wild-type strain in BALB/c mice. These results contrast with those described for other <i>Brucella</i> species, suggesting that <i>norD</i> is dispensable in <i>B. abortus</i> 2308W virulence and that in the <i>Brucella</i> genus, there are species-specific differences in the role of the <i>nor</i> operon during infection.