Transcriptional and Physiological Responses of Nitrosococcus mobilis to Copper Exposure

This research examined the dynamic physiological and transcriptional responses of Nitrosococcus mobilis, an unsquenced ammonia-oxidizing bacterium, to ${\mathrm{Cu}}^{2+}$ exposure. ${\mathrm{Cu}}^{2+}$ exposure caused decreases in N. mobilis nitrite production and oxygen uptake rates, and the release of intercellular ${\mathrm{K}}^{+}$ suggested that ${\mathrm{Cu}}^{2+}$ damaged the outer-membrane of N. mobilis cells. Shotgun DNA microarrays identified five previously unsequenced genes that were up- or down-regulated in response to ${\mathrm{Cu}}^{2+}$ exposure. The up-regulated putative efflux protein (HP 1900) and a copper containing NnrS protein (HP 1696) were found to correlate with ${\mathrm{Cu}}^{2+}$ concentrations. The up-regulation of these genes may be useful as a bioindicator of the presence of ${\mathrm{Cu}}^{2+}$ in natural and engineered systems. Finally, the expression of amoA and hao genes encoding the sole metabolic enzymes ammonia monooxygenase and hydroxylamine oxidoreductase, respectively, were measured. While hao expression did not change upon exposure to ${\mathrm{Cu}}^{2+}$, amoA expression increased upon exposure to slightly inhibitory concentrations of ${\mathrm{Cu}}^{2+}$ and decreased upon exposure to more severe inhibitory concentrations. This suggests that N. mobilis will adjust amoA expression based on available ${\mathrm{Cu}}^{2+}$ and energy.