Biased Bacteria

Mono Lake in California. In 2010, scientists reported that some bacteria taken from the lake could thrive on arsenic instead of the usual elements needed to sustain life.-AP

A FEW degrees difference in a single hydrogen bond angle prevents bacteria from importing arsenate in place of phosphate, a molecule integral to energy production and the structure of the deoxyribonucleic acid (DNA), according to a new study published in Nature. The work shows how proteins designed to import phosphate from the environment are unable to handle arsenates slightly larger size. These gatekeeper proteins enable certain bacterial species to grow in high-arsenate environments.

The study refutes the 2010 Science paper in which researchers of the National Aeronautics and Space Administration (NASA) had claimed to have discovered a strain of Halomonas bacteria in Mono Lake, California, which incorporated arsenate, instead of phosphate, into its DNA backbone (Frontline, December 31, 2010). The present research provides a mechanistic explanation for how the bacteria in Mono Lake separate enough phosphate from their environment to grow, despite the high level of arsenate in the water. While arsenate is similar in size and structure to phosphate, it is much less stable.

As a result, if the enzymes incorporated arsenate into adenosine triphosphate (ATP), it would result in a futile cycle. The cell will get no energy because the arsenate-based molecule will quickly degrade, the authors have pointed out.

In hydrogen bonds, the binding angles are very important, explained Mikael Elias, the lead author, who added that this strategy for discriminating between ions such as arsenate and phosphate was unprecedented to my knowledge. This discrimination strategy of bacteria could be applied to synthetic biology, allowing scientists to avoid side effects by designing drugs with high binding selectivity to the appropriate targets.

Stories by R. Ramachandran