Microbes from 120,000-year-old Ice Sample Show Life's Tenacity

http://live.psu.edu/story/7013

Microbes from 120,000-year-old ice sample show life's tenacity
Pennsylvania State University
May 26, 2004

University Park, Pa. -- The discovery of millions of micro-microbes
surviving in a 120,000-year-old ice sample taken from 3,000 meters below
the surface of the Greenland glacier was announced by Penn State
scientists today (May 26) at the General Meeting of the American Society
for Microbiology in New Orleans, La. The discovery may help to define the
limits for life on Earth, as well as elsewhere in the universe, such as on
cold planets like Mars.

According to Penn State's Vanya I. Miteva, research associate, and Jean E.
Brenchley, professor of microbiology and biotechnology, the majority of
the microbes they discovered in an ice-core sample taken from the glacier
were less than 1 micron in size -- smaller than most commonly known
bacteria, which range from 1 to 10 microns. In addition, a large portion
of the cells appeared to be even smaller and passed through filters with
0.2-micron pores.

The scientists are interested in understanding how microbial life can be
preserved in polar ice sheets for hundreds of thousands of years under
stresses that include subzero temperatures, desiccation, high pressures,
and low oxygen and nutrient concentrations. Because the ice was mixed with
the ancient permafrost at the bottom of the glacier, the microbes could
have been trapped there for perhaps millions of years.

"We are particularly interested in the formation of ultra-small cells as
one possible stress-survival mechanism, whether they are starved minute
forms of known normal-sized microbes or intrinsically dwarf novel
organisms, and also whether these cells are able to carry on metabolic
processes while they are so highly stressed," Miteva says.

Physiological changes that accompany the reduction of a cell's size may
allow it to become dormant or to maintain extremely low activity with
minimal energy.

"Many of these ice-core microbes are related to a variety of ultra-small
microorganisms from other cold environments that have been shown to use
different carbon and energy sources and to be resistant to drying,
starvation, radiation, and other stress factors. Their modern relatives
include the model ultra-micro bacterium Sphingopyxis alaskensis, which is
abundant in cold Alaskan waters," Brenchley reports. She and Miteva are in
the process of closely examining all the microbes they found in order to
determine the identities and diversity of the species and to look for ones
with novel functions.

The researchers used a variety of methods including repeated sample
filtrations, electron microscopy and a modified technique of flow
cytometry to quickly reveal the number of cells and to estimate their
different sizes, DNA content, and other characteristics. Miteva and
Brenchley discovered cells with many different shapes and sizes, including
a large percentage that were even smaller than filter-pore sizes of only
0.2 microns.

"It appears that these ultra-small microbes often are missed in research
studies because they pass through the finest filters commonly used to
collect cells for analysis," Miteva says.

Scientists believe these dwarf cells belong to the "uncultured majority"
because they are among the 99 percent of all microbes on Earth that never
have been isolated and cultured for study. Obtaining such "isolates" is
necessary in order to describe a new organism, study its cell size,
examine its physiology, and assess its ecological role.

"We now know just the tip of the iceberg of all the microbes that exist on
Earth, and it generally is believed that a large portion of these unknown
microbes are very small in size," Miteva says.

"A major challenge is to develop novel approaches for growing some of
these previously unculturable organisms," Brenchley says. "At present, no
single established protocol exists and little is known about the recovery
of these stressed and possibly damaged cells from a frozen environment
that subjects them to severe conditions for long periods."

Some of the cells that Miteva and Brenchley were successful in cultivating
required special conditions and up to six months to form initial colonies.
The researchers discovered that these colonies grew more rapidly during
further cultivation and that most continued to form predominantly small
cells.

"Our study of the abundance, viability, and identity of the ultra-small
cells existing in the Greenland ice is relevant to discovering how small
life-forms can be; how cells survive being small, cold and hungry; and
what new tricks we need to develop in order to cultivate these small
cells," Miteva says. "This study is part of the continuing quest by
microbiologists to overcome the current limitations of our methods and to
answer the big question, 'What new microbes are out there and what are
they doing?'"

This research was supported by the Department of Energy (Grant
DE-FG02-93ER20117) and the Penn State Astrobiology Center (NASA-Ames
Cooperative Agreement No. NCC2-1057).


Contact
Barbara Kennedy

www.science.psu.edu
814-863-4682