In the Lab
A radical solution for environmental pollution
Nature abounds with examples of bacteria that can thrive in extreme situations -- surviving on toxic chemicals, for instance. In a paper published online in the Journal of the American Chemical Society (JACS) May 25, University of Michigan researchers show how some bugs manage to do that, by using other potentially harmful chemicals known as free radicals to degrade the toxins they live on.
Such insights could lead to new ways of engineering bacteria to clean up environmental messes, said associate professor of chemistry E. Neil Marsh, who did the work with postdoctoral fellow Chunhua Qiao.
Free radicals -- highly reactive chemical species that have been implicated in aging diseases such as Alzheimer's and cancer, and even destruction of the ozone layer -- aren't all bad, Marsh said. Many essential chemical reactions occurring in living organisms involve enzymes that use radicals. In the work described in the JACS paper, Marsh and Qiao investigated the chemical reactions that allow the bacterium Thauera aromatica to live on toluene as its sole source of carbon and energy.
"Toluene is a byproduct of oil refining, so there's quite a lot of environmental contamination with this and related hydrocarbons, from refineries or chemical plants," Marsh said. "Because of their molecular structure, these compounds are very difficult to degrade, which is why they're pollution hazards." Toluene is especially worrisome because it's more soluble in water than most organic compounds, which means that it can contaminate groundwater.
Bacteria such as T. aromatica hold promise for use in cleaning up environmental pollutants because they not only can break down hazardous chemicals, but they can also do it underground, in oxygen-scarce environments -- just the sort of places where toluene could be causing problems.
Marsh would like to transfer T. aromatica's toluene-degrading abilities to other bacteria that are more easily cultured and more tolerant of various environmental conditions. He'd also like to coax T. aromatica into neutralizing other kinds of pollutants, but the first step is understanding exactly how the bug breaks down toluene.
"The challenge is that the chemical reactions these bacteria use are very unusual -- not the standard chemical reactions that chemists usually think about," said Marsh. "It turns out that the solution to metabolizing these very inert compounds is to harness the reactive chemistry of free radicals. To a chemist, it's an elegant solution to a difficult problem -- even if we still don't really understand how the enzymes that catalyze these reactions work, for everyone else it could mean less pollution."
For more information, visit http://pubs.acs.org/journals/jacsat.
A Hope For Oil Spill Bioremediation
An article in the June 2005 issue of the journal Environmental Microbiology reveals that indigenous microbiota of the Galician shore is readily able to degrade crude oil. Scientists from the Estación Experimental del Zaidín (Spanish Council for Research, CSIC) in Granada investigated in-situ crude oil degradation after the Prestige oil spill in November 2002.
After a spill, hydrocarbons are subjected to physicochemical processes such as evaporation or photochemical oxidation, which produce changes in oil composition. But the most important process acting on the spilled oil is biodegradation. It is well established that most crude oils are biodegradable to a great extent, especially components as short linear alkanes or simple aromatic hydrocarbons. However, the heavy fraction, made of long-chain saturated and polyaromatic hydrocarbons, and a considerable fraction of asphaltenes and resins, is generally recalcitrant to degradation.
The team's goal was to assess the response of the natural bacterial population after the spill and to detect evidences of crude oil degradation taking place at the contaminated sites. They used stable isotopes (13C/12C) to determine the origin of dissolved inorganic carbon (DIC) in control and contaminated coastal marine water samples. Due to its biological origin, crude oil is very depleted in 13C. Therefore, its biodegradation product carbon dioxide (CO2) will also be more 13C depleted as compared with the typical marine DIC and atmospheric dissolved CO2.
The sampling area is an energetic system poor in organic mater. Consequently, the anomalous DIC isotopic composition of certain samples taken along the shore of a contaminated island in the Cíes archipelago showed degradation of a depleted 13C source such as the Prestige crude oil, pointing to a natural population oxidizing this carbon source into CO2. This could be reproduced in the laboratory using water samples taken from the contaminated shore, although the process required nitrogen and phosphorus amendment, these two elements being limited in marine ecosystems. The results confirmed the presence of a microbiota readily able to degrade the contaminant.
Further analysis of specific organisms present in contaminated beaches revealed the presence of several populations able to degrade polycyclic aromatic compounds such as phenanthrene or naphthalene, especially in those sites that had recently been restored after an important contamination episode. Authors concluded that, probably due to the past contamination record of that coast, indigenous populations had evolved to select for organisms able to grow and degrade components of crude oil.
For more information, visitwww.blackwell-synergy.com/loi/emi.
This article originally appeared in the 09/01/2005 issue of Environmental Protection.