ENGINEERING

Spore Work Pays Off

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Science  21 Feb 2014:
Vol. 343, Issue 6173, pp. 817-818
DOI: 10.1126/science.343.6173.817-d
CREDIT: XI CHEN/COLUMBIA UNIVERSITY

The presence or absence of water on a surface or surrounding a cell can have a strong influence on its mechanical properties. This response to water gradients is useful in applications such as microfluidics or for transpiration in plants, but in principle can also generate work that might be harvested as electrical power. Chen et al. show that dormant spores of Bacillus subtilis and Bacillus thuringiensis are actually much more effective at converting energy from water gradients—in this case, changes in relative humidity—than are synthetic materials designed for this purpose. Furthermore, a mutation in B. subtilis causing a loss of most of its coating layers also confers an increase in energy density. Monolayers of assembled spores induced large deformations as a response to water potential on microcantilevers and latex sheets, and even when integrated into an energy-harvesting device.

Nat. Nanotechnol. 9, 137 (2014).

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