Procaryotes Are so Over: Pace Makes the Case

January 31, 2008 / Posted by: Wendy Dolci

Norman R. Pace, a leading scientist in the field of astrobiology, makes his case for the end of the prokaryote in the January 2008 issue of Microbe, the monthly magazine of the American Society for Microbiology (ASM).

“Put simply, the concept of prokaryote is obsolete,” Pace asserts in his article, “The molecular tree of life changes how we see, teach microbial diversity.”

According to the American Heritage Dictionary, a prokaryote is “an organism of the kingdom Monera (or Prokaryotae), comprising the bacteria and cyanobacteria, characterized by the absence of a distinct, membrane-bound nucleus or membrane-bound organelles, and by DNA that is not organized into chromosomes.” According to Pace, this definition is no longer valid.

Pace is currently a professor in the Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, and a member of the the NASA Astrobiology Institute’s University of Colorado Center for Astrobiology research team, which is studying is studying the origin of stars and planets, development of habitable planets, “RNA World” and the origins of life, biological evolution on Earth, energetics of life on other planets, and philosophical aspects of astrobiology and the search for life elsewhere. Pace is the lead member of the group on the Boulder team that is working on development and use of ribosomal-RNA-based molecular methods to survey and study the microbial constituents of ecosystems in extreme environments. Results of this research thus far include the discovery of new groups of organisms living in anaerobic environments and the identification of hydrogen (as opposed to sulfur) as the fundamental energy source for thermophilic (heat-loving) microbial communities living in Yellowstone National Park’s hot springs. Pace has also been an investigator in the Exobiology and Evolutionary Biology Program.

“In contrast to physiological properties, gene sequences provide an objective metric for evolutionary diversity,” Pace explains in Microbe. “Comparisons of sequences can be used to measure evolutionary relatedness and to construct phylogenetic trees,” which organize life into three groups – bacteria, eucarya, and archaea. But despite the evidence to support the phylogenetic tree of life, too many biology textbooks persist “continue to fail to recognize that the procaryote concept is wrong in light of what recent biology teaches us and, thus, is conceptually misleading.”

Pace is the recipient of ASM’s 2007 Abbott-ASM Lifetime Achievement Award for outstanding contributions to the field of microbial ecology. “One of Dr. Pace’s greatest contributions to microbiology,” according to ASM, “is his original insight combining molecular evolutionary and phylogenetic perspectives with microbial ecology. Dr. Pace’s seminal ideas in cultivation-independent molecular approaches have positively transformed the science of microbial evolution and ecology.” Pace’s article for Microbe is based on his ASM Lifetime Achievement Award lecture at ASM’s 2007 annual meeting in Toronto, Canada, on May 22.