Quantification of changing Pseudomonas aeruginosa sodA, htpX and mt gene abundance in response to trace metal toxicity: a potential in situ biomarker of environmental health.

Sediment-dwelling prokaryotes play a vital role in determining the fate and speciation of metals, yet are also susceptible to the biological effects of trace metals. In this article, optimized DNA extraction and purification techniques and species-specific primers are used to assess the genetic incidence and abundance of metal detoxification and general stress genes of Pseudomonas aeruginosa to complement chemical analysis in inferring the severity of metal-contaminated sites along the Clark Fork River, Montana. Results show the highest incidence of candidate genes related to bacterial stress at the most polluted site, while multiple regression analysis demonstrated significant correlations (P<0.05, r(2)=0.9) between in situ metal concentrations (As, Cu and Zn), total gene incidence, and the incidence of metal detoxification genes. Furthermore, principal components plotting the incidence of genes related to metal resistance show clear separation of sites giving clear clusters on the basis of contamination. Quantification of three genes (sodA, htpX and mt) from surveyed sites found significantly higher (anova, P<0.05) copy numbers at the more contaminated sites compared with reference sites. The development of rapid microbial biomarker tools represents a significant advance in the field of environmental biomonitoring and the prediction of metal bioavailability.

Differentiating copper and arsenic toxicity using biochemical biomarkers in Asellus aquaticus and Dreissena polymorpha.

Biomarkers of metal exposure are well known, but how a suite of such biomarkers will respond if the metal is also an oxidizing agent or causes oxidative stress is unclear. This study compares the effects of copper and arsenic, two metals with different oxidizing potential, on freshwater invertebrates. Dreissena polymorpha and Asellus aquaticus were exposed to nominal concentrations of copper (100 microg/L) or arsenic (80 microg/L) over 7 days, and physiological stress was examined by measuring metallothionein (MT) induction, thiobarbituric acid reactive substances (TBARS), and Na(+)/K(+)-ATPase activity. Both species showed increased levels of MT during 7-day Cu exposure tests and transient changes in lipid peroxidation (TBARS) which decreased to control levels by day 7. Arsenic had no effect on TBARS and only a transitory effect on MT in D. polymorpha over 7 days, although it initially induced lipid peroxidation in A. aquaticus on day 3. No inhibition of the Na(+)/K(+)-ATPase enzyme was observed for exposed organisms, and baseline values reported here, for A. aquaticus, 1.1 micromol Pi/mg/h, and for D. polymorpha, 0.38 micromol Pi/mg/h, are probably the first reported for these species.