Expression of merA, trxA, amoA, and hao in continuously cultured Nitrosomonas europaea cells exposed to cadmium sulfate additions

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

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 408 KB
• Volume: 104
• Category: Article
• ISSN: 0006-3592
• DOI: 10.1002/bit.22454

✦ Synopsis

Abstract

The effects of CdSO~4~ additions on the gene expressions of a mercury reductase, merA, an oxidative stress protein, trxA, the ammonia‐monooxygenase enzyme (AMO), amoA, and the hydroxylamine oxidoreductase enzyme (HAO), hao, were examined in continuously cultured N. europaea cells. The reactor was fed 50 mM NH~4~+ and was operated for 78 days with a 6.9 days hydraulic retention time. Over this period, six successive batch additions of CdSO~4~ were made with increasing maximum concentrations ranging from 1 to 60 µM Cd^2+^. The expression of merA was highly correlated with the level of Cd^2+^ within the reactor (Rs = 0.90) with significant up‐regulation measured at non‐inhibitory Cd^2+^ concentrations. Cd^2+^ appears to target AMO specifically at lower concentrations and caused oxidative stress at higher concentrations, as indicated by the SOURs (specific oxygen uptake rates) and the up‐regulation of trxA. Since Cd^2+^ inhibition is irreversible and amoA was up‐regulated in response to Cd^2+^ inhibition, it is hypothesized that de novo synthesis of the AMO enzyme occurred and was responsible for the observed recovery in activity. Continuously cultured N. europaea cells were more resistant to Cd^2+^ inhibition than previously examined batch cultured cells due to the presence of Mg^2+^ and Ca^2+^ in the growth media, suggesting that Cd^2+^ enters the cell through Mg^2+^ and Ca^2+^ import channels. The up‐regulation of merA during exposure to non‐inhibitory Cd^2+^ levels indicates that merA is an excellent early warning signal for Cd^2+^ inhibition. Biotechnol. Bioeng. 2009; 104: 1004–1011. © 2009 Wiley Periodicals, Inc.