杏吧原创

WHATEVER next? Environmentalists are welcoming research that could eventually
mean genetically modified bacteria cleanse the environment. The altered bugs
will help to clear chemicals that contaminate the soil of some derelict
industrial 鈥渂rownfield鈥� sites.

Chemists at Oxford University tweaked a gene from Pseudomonas putida,
a common soil bacterium, to make an enzyme that attacks three soil pollutants
called 1,2-dichlorobenzene, pentachlorobenzene and 1,3,5-trichlorobenzene. These
chemicals are used as solvents in the chemicals industry and as raw materials
for making pesticides and herbicides. Chlorobenzenes contaminating derelict
industrial sites can usually only be removed by expensive methods such as
incinerating the topsoil or removing and burying it.

Luet-Lok Wong鈥檚 team noticed that phenols, which are chemically related to
chlorobenzenes, are quickly destroyed by common soil bacteria. So they decided
to try and 鈥渟often up鈥� the pollutants by converting them into matching
phenols.

To do this, the researchers altered the gene that makes an enzyme known as
cytochrome P450_cam, which normally allows P. putida to live on
camphor. The altered gene replaces certain key amino acids in the enzyme with
bulkier alternatives. This tightens up the cleft where camphor normally docks so
that it grips any of the three chemical solvents instead. 鈥淭he secret was
recognising which ones to change,鈥� says Wong.

When the altered gene was inserted into E. coli bacteria it produced
an enzyme that changed all three chlorinated benzenes into phenols. The chemists
now hope to tweak the enzyme further to make it attack commoner, more hazardous
pollutants such as cancer-causing dioxins, PCBs and benzo[&agr;]pyrenes.

The researchers have already stitched the gene which manufactures the
strengthened enzyme back into common soil bacteria. However, they have no
intention of scattering the bacteria on contaminated sites, at least for now. 鈥淚
myself would not agree to it unless all the proper safeguards were in place,鈥�
says Wong. Instead, the researchers hope to wash the pollutants off the soil,
drain off the water, and treat it in a confined 鈥渂ioreactor鈥� containing the
altered bacteria.

Environmentalists seem happy with the compromise. 鈥淚f it was kept in a
contained situation, it could be a promising method for treating intractable
waste,鈥� says Sue Mayer of the environmental lobby group GeneWatch UK.

Paul Johnston, principal scientist at Greenpeace鈥檚 research laboratories in
Exeter, also backs further work priming the enzyme to attack dioxins and PCBs.
But he cautions that chlorophenols created when the altered enzymes attack
pentachlorobenzene could react chemically and combine to form the more hazardous
dioxins.