Physiological roles of an <i>Acinetobacter</i> -specific σ factor

<i>Acinetobacter baumannii</i> is a hospital-acquired pathogen, and many strains are resistant to multiple antibiotics. Understanding how <i>A. baumannii</i> senses and responds to stress may uncover novel routes to treat infections. Here, we examine how the <i>Acinetobacter</i>-specific transcription factor, SigAb, mitigates stress. We find that SigAb directly regulates only a small number of genes, but indirectly controls hundreds of genes that have substantial impacts on cell physiology. We show that SigAb is required for maximal growth, even during optimal conditions, and is acutely required during growth in the presence of elevated copper. Given that copper toxicity plays roles in pathogenesis and on copper-containing surfaces in hospitals, we speculate that SigAb function may be important in clinically relevant contexts.