Expression of merA, amoA and hao in continuously cultured Nitrosomonas europaea cells exposed to zinc chloride additions

✍ Scribed by Tyler S. Radniecki; Lewis Semprini; Mark E. Dolan

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 268 KB
• Volume: 102
• Category: Article
• ISSN: 0006-3592
• DOI: 10.1002/bit.22069

✦ Synopsis

The effects of ZnCl 2 additions on a mercuric reductase, merA, ammonia monooxygenase, amoA, and hydroxylamine (NH 2 OH) oxidoreductase, hao, gene expression were examined in continuously cultured Nitrosomonas europaea cells. The reactor was operated for 85 days with a 6.9 d hydraulic retention time and with four successive additions of ZnCl 2 achieving maximum concentrations from 3 to 90 mM Zn 2þ . Continuously cultured N. europaea cells were more resistant to Zn 2þ inhibition than previously examined batch cultured cells due to the presence of Mg 2þ in the growth media, suggesting that Zn 2þ enters the cell through Mg 2þ import channels. The maximum merA upregulation was 45-fold and expression increased with increases in Zn 2þ concentration and decreased as Zn 2þ concentrations decreased. Although Zn 2þ irreversibly inactivated ammonia oxidation in N. europaea, the addition of either 600 mM CuSO 4 or 2250 mM MgSO 4 protected N. europaea from ZnCl 2 inhibition, indicating a competition between Zn 2þ and Cu 2þ /Mg 2þ for uptake and/or AMO active sites. Since ZnCl 2 inhibition is irreversible and amoA was up-regulated at 30 and 90 mM additions, it is hypothesized that de novo synthesis of the AMO enzyme is needed to overcome inhibition. The up-regulation of merA during exposure to non-inhibitory Zn 2þ levels indicates that merA is an excellent early warning signal for Zn 2þ inhibition.