Expression of merA, trxA, amoA, and hao in continuously cultured Nitrosomonas europaea cells exposed to cadmium sulfate additions.
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 microM 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.
Radniecki
Tyler S
TS
School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis, Oregon 97331-3212, USA. tyler.radniecki@oregonstate.edu
Semprini
Lewis
L
Dolan
Mark E
ME
D001426:Bacterial Proteins / Q000096:biosynthesis*; D019149:Bioreactors / Q000382:microbiology; D019187:Cadmium Compounds / Q000378:metabolism*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D043370:Nitrosomonas europaea / Q000187:drug effects* / Q000235:genetics / Q000502:physiology*; D010088:Oxidoreductases / Q000096:biosynthesis; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D013312:Stress, Physiological; D013431:Sulfates / Q000378:metabolism*; D013879:Thioredoxins / Q000096:biosynthesis
D001426:Bacterial Proteins; D019187:Cadmium Compounds; D000644:Quaternary Ammonium Compounds; D013431:Sulfates; D013879:Thioredoxins; C037123:cadmium sulfate; D010088:Oxidoreductases; C021551:mercuric reductase; C021401:hydroxylamine dehydrogenase; C045582:ammonia monooxygenase