EMBARGOED UNTIL 2 p.m. E.D.T.
NSF PR 02-24 - April 17, 2002
Microbiology Team Probes Bacterium's Surprising
A team of microbiologists affiliated with the University
of Massachusetts at Amherst (UMass) has uncovered
the unusual survival strategies used by a common bacterium.
The finding could have implications in cleaning up
contaminants ranging from petroleum to uranium. Results
of the National Science Foundation (NSF)-funded study
by UMass microbiologist Derek Lovley and colleagues
will be published in the April 18 issue of Nature.
The research was also funded by the U.S. Department
Scientists have long known that the bacteria species,
Geobacter metallireducens, is commonly found
in soil and consumes metals - specifically, iron and
manganese oxides. The new findings detail the microorganisms'
intriguing survival tactics. First, the species is
apparently able to locate and home in on the metal
that serves as its food source. "This is the first
microorganism found to have a built-in sensor that
allows it to essentially 'sniff out' metals," said
Lovley. And if a source of iron or manganese is not
nearby, the bacterium - which was previously believed
to be incapable of movement - can essentially decide
to grow flagella, the whip-like structures that enable
bacteria to swim.
"This work demonstrates again that basic research,
in addition to answering the questions for which it
was specifically designed, can also produce totally
unexpected insights into the natural world," says
Susan Porter Ridley, program director in NSF's division
of molecular and cellular biosciences. "In this case,
the sequence of bases in a microbe's DNA led to the
discovery that the microbe can actually sense and
locate chemicals it needs. This knowledge, in turn,
shows great promise for helping us solve the problem
of environmental pollution."
Scientists were already aware that some bacteria species,
such as the well-studied E coli, are able to
sense and swim toward sugars. But scientists had
never seen Geobacter swim, leading UMass researchers
to wonder how it is that metals serve as its energy
Clues to the puzzles were found as Geobacter's
genome was sequenced in collaboration with The Institute
for Genomic Research in Rockville, Maryland. The
Geobacter's genetic code revealed a startling
discrepancy: "We looked at the complete genetic code,
and saw clear evidence of genes for flagella, so we
realized this bacterium does indeed have the genetic
potential to swim," said Lovley. "The question then
was, 'Does this have anything to do with Geobacter's
growth on metals?'"
Lovley realized that in previous studies the ability
of Geobacter to swim had always been analyzed
when it had been grown on soluble metals, which are
often used in laboratory experiments because they
are easy to work with. No one had looked carefully
at growth on the metal oxides that Geobacter
actually uses in natural environments. When the researchers
looked at cultures grown on iron oxide, the cells
had produced flagella and were swimming.
The genome also contained genes which suggested that
Geobacter might be able to sense chemicals
in the environment. To see if this was also related
to growth on metals, the scientists set up a series
of microscope slides on which the bacteria needed
to travel to reach the metal necessary for their survival.
It turned out that the bacteria were growing flagella
and swimming to the metal source. "These bacteria
really do grow flagella in order to search for, and
establish contact with, the soluble iron or manganese
oxides they need," paper co-author Susan Childers
said. Under the microscope, the microbes are cigar-shaped,
and one to two microns long; 10,000 of them would
measure an inch.
Once the bacterium reaches the metal, it is able to
grow the short, hair-like structures called pili,
which allow the bacterium to anchor itself to the
metal source, ensuring growth.
The finding represents more than just an intriguing
look at how microbes survive and thrive: these microbes
can be used to clean up petroleum spills, and they
may offer an efficient and economic solution to removing
uranium from contaminated groundwater. Previous efforts
at flushing uranium from the soil involved pumping
water out of an area and removing the soil - a process
which has proven to be both expensive and inefficient,
"Geobacters don't actually remove the uranium,"
explained Lovley, "but they do transform the metal
from a soluble form to an insoluble form, so that
it is no longer able to leach into the groundwater
and eventually contaminate rivers."