Microbiologist Harry Kurtz and geologist Dennis Netoff of the Sam Houston
State University in Huntsville, Texas, have discovered that sandstone contains
communities of photosynthetic cyanobacteria. These protect friable sandstone
from the ravages of rain and wind, the researchers believe. They hope the
cyanobacteria can be cultivated to help preserve damaged hiking trails.

The researchers took samples of crushed sandstone and added a solution
containing bicarbonate, to give the microorganisms a source of a carbon. After
three months, the sand turned distinctly green, showing that a thriving
community of cyanobacteria had grown up.

More importantly, the sand grains had coalesced into a hardened mass. “And
you could feel that the surface was harder where it was greener,” says Kurtz.
Further analysis revealed that the cyanobacteria were making acidic
polysaccharides, starches that can bind to metal ions to produce a tough
matrix.

Kurtz thinks that the same process happens in natural sandstone, which often
has a rippled surface. “You can see the ridges are greener than the
depressions,” he says. “The cyanobacteria colonise the ridges, making them
harder to erode.”

In the arid western US, the formation of the protective matrix is presumably
limited by the availability of water, which frees metal ions from the rock. But
Kurtz and Netoff believe that damaged sandstone could be preserved by spraying
it with water spiked with the necessary metal ions.

The research, by John Quensen and his colleagues at Michigan State
University, was partly funded by the Montrose Chemical Corporation, which was a
major DDT manufacturer. The group incubated DDE-contaminated sediments taken
from the ocean floor under conditions that encouraged bacterial growth, and
measured the degradation of DDE (Science, vol 280, p 722).

Over a 32-week period, anaerobic bacteria in the sediments degraded over half
the DDE into a biodegradable product DDMU.

Quensen claims the data could change DDT’s reputation. “They suggest the need
to re-evaluate environmental risk assessment.” He thinks the microbes could
clean up contaminated sites.

But Hazel Mathews, a chemist with the National Institute of Environmental
91ɫ��Ƭ Sciences in Research Triangle Park, North Carolina, says that in their
natural setting the microbes may not destroy DDE so readily. Mathews also doubts
that these microbes could clean up contaminated sites. “There is no telling if
these marine microbes, when cultured and released in affected sites, will be
able to compete with surface microbes.”