For just about every chemical, there's a bacteria that breaks it down. Scientists would like to take advantage of bacteria to clean up pollution, but they've found it difficult to pick out the useful bugs at a contaminated site from those just hanging around. Now a research team has used a mix of genetics, ecology, and molecular biology to ID an organism that breaks down the pollutant naphthalene in dirt.
Screening bacteria for pollution-gobbling prowess is difficult, in part because about one out of every 10,000 species can be grown in the lab. And even when scientists are able to culture a bug, they are rarely sure of what it does in the wild. In 2000, scientists proposed finding bacteria that eat a certain chemical by feeding them the compound tagged with radioactive carbon-13. The technique worked well in lab experiments, but when Eugene Madsen, a microbiologist at Cornell University, and colleagues saw the study, they wondered if the technique could locate bacteria in the field.
They went to an aquifer with naphthalene-contaminated dirt and released carbon-13-tagged naphthalene. They put glass jars on top of the area and tested for carbon dioxide enriched with carbon-13--an indicator that the soil contained bugs that metabolize the chemical. When this test came up positive, they analyzed the DNA from a soil sample and looked for strands that had incorporated the carbon-13. One such sequence served as the "signature" of the species that was eating naphthalene. They then cultured bacteria from the site and isolated the strain whose DNA matched their signature sequence, they report online this week in the Proceedings of the National Academy of Sciences.
The interesting thing about the research is that Madsen's team was able to isolate the organism that was actually responsible for what they saw in the field, says microbial biologist Norman Pace of the University of Colorado, Boulder. Similar methods may help find the best species to clean up areas polluted with other compounds, he says.