Expression of merA,trxA, amoA,and hao in continuously cultured Nitrosomonas europaea cells exposed to cadmium sulfate additions |
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Authors: | Tyler S. Radniecki Lewis Semprini Mark E. Dolan |
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Affiliation: | School of Chemical, Biological and Environmental Engineering, Oregon State University, 102 Gleeson Hall, Corvallis, Oregon 97331‐3212 |
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Abstract: | The effects of CdSO4 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 NH4+ and was operated for 78 days with a 6.9 days hydraulic retention time. Over this period, six successive batch additions of CdSO4 were made with increasing maximum concentrations ranging from 1 to 60 µM Cd2+. The expression of merA was highly correlated with the level of Cd2+ within the reactor (Rs = 0.90) with significant up‐regulation measured at non‐inhibitory Cd2+ concentrations. Cd2+ 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 Cd2+ inhibition is irreversible and amoA was up‐regulated in response to Cd2+ 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 Cd2+ inhibition than previously examined batch cultured cells due to the presence of Mg2+ and Ca2+ in the growth media, suggesting that Cd2+ enters the cell through Mg2+ and Ca2+ import channels. The up‐regulation of merA during exposure to non‐inhibitory Cd2+ levels indicates that merA is an excellent early warning signal for Cd2+ inhibition. Biotechnol. Bioeng. 2009; 104: 1004–1011. © 2009 Wiley Periodicals, Inc. |
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Keywords: | Nitrosomonas europaea chemostat CdSO4 merA amoA trxA |
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