Researchers find mechanism bacteria use to target specific chemical contaminants

New insight into the molecular-level interactions between bacteria and minerals may some day help scientists design bacteria with the express purpose of cleaning up toxic waste.

Hazardous waste experts know that certain bacteria can essentially eat toxic waste, reducing it to less noxious substances. But until now they didn’t know what mechanisms allowed these bacteria to devour chemicals.

A new study by Ohio State and Virginia Tech universities showed how a particular bacteria uses iron oxide, or rust, to breathe. The researchers found that key changes in the expression of genes in Shewanella oneidensis enable the microbe to recognize and bind specifically to iron oxides.

This finding could help researchers manipulate the bacteria to make it more effective in cleaning up petroleum products at toxic waste sites.

“In some situations, S. oneidensis is capable of using organic contaminants similar to oil as a source of energy,” said Steven Lower, a study co-author and an assistant professor of geological sciences at Ohio State. “Petroleum products are one of the main chemicals found in toxic waste dumps.

“Also, there’s little to no oxygen in these underground sites, so the bacteria have to adapt to anaerobic conditions,” said Lower, who is also a professor in the school of natural resources. This essentially means that in order for bacteria to grow and degrade an organic contaminate, it must be able to ‘breathe’ on something other than oxygen.”

The researchers hope to one day be able to tailor bacteria so it could target a specific contaminant.

Lower pointed out that one problem with using microbes to help clean up contaminated sites is getting the bacteria to the site and then ensuring that it remains in place.

Knowing which gene the bacteria express in an anaerobic environment may enable researchers to genetically manipulate the microbes so they prefer iron oxides only in the presence of oil and related waste products.

Lower conducted the work with Brian Lower and Michael Hochella, both with the department of geosciences at Virginia Tech. The results were presented December 8 at the fall meeting of the American Geophysical Union in San Francisco.

The researchers used a relatively new technique called biological force microscopy to measure the molecular forces between S. oneidensis and a crystal of iron oxide. Force microscopy lets scientists measure the minutest interactions between the surfaces of two substances. Such microscopes use an ultra-sensitive probe that can detect attractive and repulsive forces.

The researchers placed a small amount of S. oneidensis on the probe, which also acts as a cantilever, and a sample of iron oxide near the probe. A beam of laser light was then reflected off of the probe to determine if the bacteria-covered cantilever was bending toward or away from the iron oxide sample, and by how much.

“In principle it’s a very simple measurement that tells us whether or not a bacterium is attracted to an inorganic substance, and also gives us a precise measurement of that attraction,” Lower said.

He and his colleagues also analyzed gene expression patterns in S. oneidensis to learn if different genes were expressed depending on what the bacteria uses to breathe.

Indeed, the researchers found that S. oneidensis produces two specific proteins under anaerobic conditions, which allow the microbes to bind to and breathe in, and therefore reduce, iron contained in the structure of a solid mineral.

“We’ve known for decades that this bacteria can use dissolved iron to breathe, but until now we really didn’t know how they could do this in nature, where most of the iron is embedded in the crystal structure of a solid mineral,” Lower said. “This interaction is probably billions of years old, and may represent one of the first globally significant mechanisms for oxidizing organic matter to carbon dioxide.”

This work was supported by grants from the U.S. Department of Energy and the National Science Foundation.

Contact: Steven Lower, (614) 292 1571; Lower.9@osu.edu
Written by Holly Wagner, (614) 292-8310; Wagner.235@osu.edu