Bacteria clean up by breathing rust

New insights into how bacteria interact with minerals could help scientists 'design' microorganisms to clean up specific types of toxic waste, according to researchers from Ohio State and Virginia Tech Universities.

The team, including geoscientists from both universities, has found how a particular bacterium, Shewanella oneidensis, attaches itself to particles of iron oxide and uses them to breathe.

Using bacteria to clean up toxic wastes is a long-established technique, but it isn't well understood. Many bacteria are able to digest organic compounds, such as those found in contaminated sites, but they need oxygen to do this, and sometimes the contaminants are located in oxygen-deprived areas.

'The bacteria have to adapt to anaerobic conditions,' says Steven Lower of Ohio State University, one of the paper's authors. 'This essentially means that in order for the bacteria to grow and degrade an organic contaminant, it must be able to 'breathe' on something other than oxygen.'

S. oneidensis has been known to possess this ability for many years, Lower says, but the mechanism was unknown until now. Experiments with atomic force microscopes revealed that the bacteria are attracted to iron oxide, but genetic studies revealed the mechanism. It appears that when the oxygen levels are low, the bacterium expresses two proteins that bind onto and reduce iron oxides which are contained within solid minerals.

The researchers have identified the genes which express these proteins, and it's this discovery which might make it possible to tailor other bacteria to tackle organic pollutants. Lower points out that the difficulty with bacterial clean-up is getting the bacteria to the site and ensuring that they stay in place.

Using genes similar to those of S. oneidensis might allow them to engineer microbes which bind onto iron oxides only in the presence of oil and related waste products.