Genome-Wide Transcriptional Response of Chemostat-Cultured<i>Escherichia coli</i>to Zinc

<jats:title>ABSTRACT</jats:title><jats:p>Zinc is an essential trace metal ion for growth, but an excess of Zn is toxic and microorganisms express diverse resistance mechanisms. To understand global bacterial responses to excess Zn, we conducted transcriptome profiling experiments comparing<jats:italic>Escherichia coli</jats:italic>MG1655 grown under control conditions and cells grown with a toxic, sublethal ZnSO<jats:sub>4</jats:sub>concentration (0.2 mM). Cultures were grown in a defined medium lacking inorganic phosphate, permitting maximum Zn bioavailability, and in glycerol-limited chemostats at a constant growth rate and pH. Sixty-four genes were significantly up-regulated by Zn stress, including genes known to be involved in Zn tolerance, particularly<jats:italic>zntA</jats:italic>,<jats:italic>zraP</jats:italic>, and<jats:italic>hydG</jats:italic>. Microarray transcriptome profiling was confirmed by real-time PCR determinations of<jats:italic>cusF</jats:italic>(involved in Ag and Cu efflux),<jats:italic>ais</jats:italic>(an Al-inducible gene),<jats:italic>asr</jats:italic>(encoding an acid shock-inducible periplasmic protein),<jats:italic>cpxP</jats:italic>(a periplasmic chaperone gene), and<jats:italic>basR</jats:italic>. Five up-regulated genes,<jats:italic>basR</jats:italic>and<jats:italic>basS</jats:italic>[encoding a sensor-regulator implicated in<jats:italic>Salmonella</jats:italic>in Fe(III) sensing and antibiotic resistance],<jats:italic>fliM</jats:italic>(flagellar synthesis), and<jats:italic>ycdM</jats:italic>and<jats:italic>yibD</jats:italic>(both with unknown functions), are important for growth resistance to zinc, since mutants with mutations in these genes exhibited zinc sensitivity in liquid media and on metal gradient plates. Fifty-eight genes were significantly down-regulated by Zn stress; notably, several of these genes were involved in protection against acid stress. Since the<jats:italic>mdt</jats:italic>operon (encoding a multidrug resistance pump) was also up-regulated, these findings have important implications for understanding not only Zn homeostasis but also how bacterial antibiotic resistance is modulated by metal ions.</jats:p>