Research M Watch A single enzyme may be all that is keeping 455 gigatonnes of stored carbon from being released into the atmosphere, concludes a report by researchers at the University of Wales. That large amount of carbon, which represents 20–30% of the world’s soil carbon stock, is tied up in northern peatlands (wetlands that accumulate greater than 30 cm of organic peat). If the activity of just one enzyme could release this carbon, the finding may have serious implications for future global warming. It is well known that peatlands remove carbon dioxide from the atmosphere faster than they release it, but why has been unclear. Chris Freeman and co-workers believe they have now found the answer, based on a simple observation that phenolic compounds are ubiquitous in all peatlands. Phenolic compounds inhibit biodegradation, which could explain why the carbon is being released so slowly. The researchers attribute the buildup of phenolic material in peatlands to the lack of activity of one particular enzyme— phenol oxidase. Although phenol oxidase exists under anaerobic conditions, such as those commonly found in peatlands, its activity is severely restricted in the absence of oxygen. To test their hypothesis that oxygen constraints on phenol oxidase lead to the buildup of phenolics and the slow biodegradation rates observed in peatlands, the researchers compared the activity of several enzymes, including sulphatase, phophatase, -glucosidase, and phenol oxidase, under oxygen-saturated and oxygen-free conditions. Phenol oxidase was the only enzyme found to increase in activity under more aerated conditions. Furthermore, increasing the amount of phenol oxidase significantly decreased the levels of phenolic compounds (Nature 2001, 409, 149).
Chlorobenzene bug
dechlorinates higher chlorobenzenes to lower, less toxic forms. One difference between the two organisms, the researchers point out, is that D. ethenogenes requires supplements to grow, whereas CBDB1 grows on purely synthetic material (Nature 2000, 408, 580–583).
A strain of bacteria that thrives on chlorinated benzenes has been identified by researchers at Technische Universität and Robert Koch Institut in Berlin. The highly specialized bacterium, called CBDB1, could be useful for remediating sites contaminated with chlorobenzenes, which are considered persistent, toxic, and bioaccumulative.
Clams document decline LORENZ ADRIAN AND JÖRG WECKE
Enzyme found key to carbon storage
Bacteria thatdegrade chlorobenzenes.
Lorenz Adrian and colleagues isolated the CBDB1 strain from a bioreactor containing a mixed culture enriched with dechlorinating bacteria and found that its growth occurred only in the presence of chlorobenzenes, hydrogen, and acetate. Hydrogen acts as an electron donor and chlorobenzene as an electron acceptor. Although reductive dechlorination by mixed cultures has been previously shown, this is the first time a pure culture has been shown to be capable of dechlorinating chlorobenzenes. Just as Dehalococcoides ethenogenes dechlorinates perchloroethene to nontoxic ethene, the CBDB1 strain
The Colorado River delta’s mollusk population has dropped precipitously in the 70 years since the river was first diverted for dams and irrigation, according to research conducted by a group of American and Mexican scientists. The study uses mollusks as an indicator to show that the diversions triggered the “collapse of the Colorado delta ecosystem.” Led by Karl Flessa of the University of Arizona and Michal⁄ Kowalewski of Virginia Polytechnic Institute and State University, the study integrated paleontological records with geomorphological, geochemical, and geochronological data to reach its conclusions about human impact on the coastal ecosystem. Bivalve mollusks constitute more than 99% of the shell material deposited on the beach of the delta where the Colorado River empties into the Gulf of California, and they serve as a proxy for the estuary’s benthic productivity. The researchers used amino acid racemization analysis to determine the age of 125 representative shells and found that shells less than 50 years in age are rare. They calculated that 50 mollusks, on average, occupied each square meter of beach during the past millennium. The mollusk’s population density is now more than an order of magnitude lower at ~3 individuals/m2. The scientists blame the clam population implosion on the dramatic decline in fresh water and nutrients reaching the delta, as well as the increase in pollutants associated with agricultural wastewater, such as selenium. The evidence suggests that al-
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though the delta ecosystem has been partially restored in recent years, its marine population is unlikely to rebound (Geology 2000, 28 (12) 1059– 1062).
Liquidating pharmaceutical waste Using ionic liquids can significantly reduce the amount of waste required for synthesizing a nonsteroidal antiinflammatory drug called Pravadoline, Irish researchers have found. They claim that it is the first high-yielding process to employ a room-temperature ionic liquid for devising a pharmaceutical product. The relative efficiency of different methods for producing pharmaceuticals can be compared by calculating their E-factors, the ratios of byproducts to the desired products formed. It is not unusual for pharmaceutical processes to have E-factors of 25 to 100, and some have E-factors of over 1000. Although Kenneth Seddon and his colleagues at The Queen’s University of Belfast did not calculate an E-factor for the new method of synthesizing Pravadoline because it is laboratory-scale, they stress that the method’s reuse and recycling of the ionic liquid makes its waste production particularly low. Ionic liquids, which typically consist of nitrogen-containing organic cations and inorganic anions, can be used as solvents for a number of reactions. The conventional method for synthesizing Pravadoline involves two classes of reactions that are known to work very efficiently in ionic liquids, regioselective nucleophilic displacement reactions and Friedel–Crafts reactions. The new method for devising the drug allows the entire process to be carried out in the ionic liquid known as 1-butyyl-3-methylimidazolium hexafluobrophosphate, or [bmin][PF6]. One of the reasons this new method is more efficient is that it avoids the need for a dipolar, aprotic solventsome of which, like dimethyl sulfoxide, are noxiousand the base chemicals that must be used with it. It also avoids the use of Lewis acids and the aluminum waste disposal problem associated with conventional Friedel–Crafts reactions. The new method also uses less energy because it does not require heating (Green Chem. 2000, 2, 261–262). 104 A
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Detecting hepatitis in drinking water In developing countries, outbreaks of infectious hepatitis A and E have been linked to the associated viruses lurking in drinking water. Unfortunately, virus detection has proven difficult. Even worse, the incubation period is typically four weeks, so that the disease surfaces long after the population has been exposed. N. Jothikumar and co-workers at the National Environmental Engineering Research Institute in Chennai, India, have developed a method based on the DNAamplifying polymerase chain reaction (PCR) that quickly and simultaneously identifies hepatitis A and E viruses in water and offers a means for water quality surveillance. The procedure draws on PCR methods to detect enteric viruses. The hepatitis viruses are collected on granular activated carbon, concentrated, and removed off the carbon with urea arginine phosphate buffer. Because hepatitis A and E are retroviruses that contain RNA instead of DNA, reverse transcription is used to construct complementary DNA strands. The DNA is then amplified by PCR containing two sets of primers that are specific for the different hepatitis viruses. Southern blot analysis confirms the presence of the viruses. The entire procedure takes a few days. The authors demonstrated the method by screening water samples taken from 23 locations in the city of Chennai. Nine samples tested positive for hepatitis A and three for hepatitis E ( J. Environ. Monit. 2000, 2, 587–590).
Accounting for climate change Rigorous testing of a powerful climate change model has led a team of U.K. scientists to conclude that both natural and anthropogenic forcings contributed significantly to observed temperature changes that occurred during the 20th century. The coupled ocean–atmosphere general circulation model, HadCM3, has also been used to predict that global warming is likely to continue at a rate similar to that observed in the past 30 years. Modeling results indicate that Earth’s global mean temperature could change by 3 ˚C by 2100 relative to 1880–1920. The prediction is based on an Intergovern-
ENVIRONMENTAL SCIENCE & TECHNOLOGY / MARCH 1, 2001
mental Panel on Climate Change emissions scenario, which makes assumptions about future demographic and technological changes and economic development. The modeling simulations considered anthropogenic drivers, such as changes in greenhouse gases, tropospheric and stratospheric ozone sulfur emissions, the influence of sulfate aerosols on planetary albedo, and that of tropospheric aerosols on cloud reflectivity. Effects due to naturally occurring changes in aerosol amounts following volcanic eruptions and changes in solar irradiance were also considered. According to Peter Stott and co-workers at the Hadley Centre for Climate Prediction and Research in Berkshire and M. Allen of the Rutherford Appleton Laboratory in Oxfordshire, the good agreement found between model predictions and historic data increases their confidence that the model can successfully predict the anthropogenic contribution of future temperature changes (Science 2000, 290, 2133–2137).
When nitrogen-fixing trees foster carbon sequestration Tropical tree plantations that include nitrogen-fixing trees sequester much more carbon than areas with only one kind of tree, finds a team of Colorado State University researchers. The results inform efforts to use tropical tree plantations as sinks for excess carbon dioxide, the major driver of global climate change. The researchers compared carbon storage on a former sugar cane farm in Hawaii, which had 17-year-old stands of eucalyptus trees alone, nitrogen-fixing albizia trees alone, and the cash crop eucalyptus interplanted with albizia. Plots with both species contained twice as much carbon in trees as did plots with only one species. Although plots with pure albizia had more carbon in the soil, plots with both eucalyptus and albizia had the most combined aboveand below-ground carbon. The study is the first to suggest that additional nitrogen may slow decomposition of soil carbon in the field, aiding carbon sequestration. The results could influence how carbon sequestration credits are measured for global climate change treaties (Ecology 2000, 81, 3267–3273).
