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Extreme Microbes Hint at Possible Lifeforms in the Universe

Joyce_divehole Oxygen, one of the by-products of photosynthesis by microbes such as cyanobacteria and their descendants -including algae and higher plants, transformed the Precambrian Earth and made possible the evolution of more complex organisms. Jeffrey Touchman, assistant professor in the School of Life Sciences at Arziona State University is doing groundbreaking resaerch to illuminate large gaps in the available genetic data for photosynthetic microbes through the study of  organisms known as phototrophic extremophiles living in unusually harsh and exotic environments such as the buried lakes of Antarctica where a biodiversity of extremophilic anoxygenic bacteria are known to exist.
Touchman's research is focused on genome sequencing and molecular analyses of heliobacteria, proteobacteria and a cyanobacterium with the ability to shift into anoxygenic (oxygen-free) photosynthesis in the presence of sulfide, a possible evolutionary “missing link” between anoxygenic and oxygenic photosynthetic organisms.

Touchman, who is also an adjunct investigator at The Translational Genomics Research Institute (TGen), has chosen his photosynthetic, microbial partners carefully; each bears a unique metabolism, physiology or ecology and differs in fundamental ways from sequenced genomes of any other phototroph. Hidden in these organisms’ various genetic codes may be hallmarks: traces of early evolutionary innovations pointing to the origin of oxygen-evolving high-energy photosynthesis.

There are important linkages between Touchman’s work on earthbound origins and astrobiology. "Phototrophic extremophiles are excellent model microbes for studies of interplanetary photosynthetic exchange," Touchman said. 

Embedded within the genetic codes of these extremophile organisms, he believes, there may be traces of early evolutionary innovations, hallmarks that led the earliest life forms on Earth to developing oxygen-evolving high-energy photosynthesis. 

"Oxygen is a central biosignature or fingerprint of life sought in the atmospheric spectra of planets beyond our solar system. Detailed molecular understanding of how photosynthetic microbes can push the boundaries of extreme-environment existence on our own planet will also fill important gaps in our current understanding of extra-terrestrial potential for oxygen-evolving photosynthesis,” Touchman adds. “Some microorganisms can survive interplanetary journeys cocooned inside rocks blasted off planets by comet and asteroid impacts. That rocky panspermia is an effective mechanism for spreading life within a planetary system,” adds the director of the ASU Beyond Center for Fundamental Concepts in Science, Paul Davies. The arrival of oxygenic photosynthesis via transport of materials by external means, such as meteorites, could profoundly change the direction of biological evolution on a planet’s surface.

Paul Davies, director of ASU’s Beyond Center for Fundamental Concepts in Science, developed some of the thinking upon which Touchman’s extraterrestrial pursuits are based.

"Some micro-organisms can survive interplanetary journeys cocooned inside rocks blasted off planets by comet and asteroid impacts," he said. "That rocky panspermia is an effective mechanism for spreading life within a planetary system.

Casey Kazan


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