Mat-like photoautotrophic microbial communities thrive in volcanic vents, or fumaroles, at 6,051 meters above sea level, making this the highest known natural microbial habitat, according to microbial ecologist Steve Schmidt from the University of Colorado, Boulder, and his collaborators. Meanwhile, drawn from a nearly opposite extreme habitat, the ultrasmall brown-purple microorganism Herminiimonas glaciei sp. nov. recently earned the distinction of being the "only species isolated from Greenland ice that has been fully characterized and validly named," according to Jennifer Loveland-Curtze of Pennsylvania State University in State College and her collaborators.
  
Dormant cells of H. glaciei were extracted from ice cores that were drilled from 3,042 meters below the surface of the Greenland ice sheet 15 years ago and stored at the National Ice Core Laboratory. After being held anaerobically for many months in liquid culture and then plated on tryptic soy agar at low temperature, one of the core samples recently yielded viable ultra-microbacteria, whose cells are 50-fold smaller than those of Escherichia coli. The brown-purple bacteria had been dormant for at least 120,000 years, according to Loveland- Curtze and her collaborators. Details of their findings are published in the June International Journal of Systematic and Evolutionary Microbiology (59:1272-1271, 2009).

Ultra-microbacteria should not be confused with nanobacteria, Loveland-Curtze says. "The existence of nanobacteria is questioned by many scientists, whereas ultra-microbacteria . . . predominate in many environments, with some species being fully characterized and officially validated." Meanwhile, Schmidt from the University of Colorado and his collaborators collected specimens from fumarolic and nonfumarolic soils on Socompa volcano, located between Argentina and Chile, in February 2008, when temperatures sometimes fluctuated from -10 to  50°C within one day. The nonfumarolic soils, which contained mainly actinobacteria and fungi, were extremely dry and almost devoid of organic nutrients. In contrast, the fumarolic soils had adequate moisture and nutrients, supporting a broad assortment of phototrophs, according to Schmidt. Details appear in Applied and Environmental Microbiology (75:735- 747, 2009).

Do phototrophs and other microorganisms hitchhike to the tops of volcanoes? "The bacteria that are in the nonfumarolic soils are mostly of the Spartinobacteria group of the Verrucomicrobia," Schmidt says. "They probably . . . blew in on winds as dormant spores attached to dust particles. The phototrophs that live near the fumaroles are very diverse, encompassing many groups of algae and cyanobacteria. All these phototrophs are intensely pigmented-almost black rather than green-indicating their biggest stressor is the intense UV radiation at over 6,000 meters." Little else is known, he adds, about "where these phototrophs are coming from and what adaptations are needed for them to survive in such a harsh environment."

"Recently geologists recognized the all-pervasiveness of microbial communities . . . on Earth," says geologist David Krinsley of the University of Oregon, Eugene. Fumarolic soils on Socompa volcano support "diverse microorganisms," whereas nonfumarolic soils, which are poor in nutrients but otherwise comparable, support relatively simpler and fewer microorganisms. "Thus nutrients are important and temperatures and air pressures less so, [suggesting] that the planet Mars could support microbial communities if the necessary nutrients were present," he says.

"The work of Loveland-Curtze and her collaborators demonstrates the patience required to isolate microorganisms that colonize low temperature environments," says Jill Mikucki, a geomicrobiologist from Dartmouth College in Hanover, N. H. who specializes in subglacial ecosystems. "Their effort provides the research community with a new cultured representative from icy environments.

Understanding the physiology and genomic machinery of this deep-ice isolate will improve our perspective on icy life in general and will assist with formulating the next generation of questions regarding microbial survival in ice." Both of these research examples are "highly relevant to the search for evidence of life on Mars," adds Christopher McKay of the National Aeronautics and Space Administration Ames Research Center in Mountain View, Calif.

Barry E. DiGregorio
Barry E. DiGregorio is a freelance writer in Middleport, N.Y.

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