E-Book Overview
Although they comprise one of the three fundamental branches of life, it was only the last decade that Archaea were formally recognized as a group alongside Eukaryotes and Bacteria. Bacteria-like in that they are single celled organisms that lack a nucleus and intracellular organelles, the Arachaea also share a large gene set typical of eukaryotes, for making and repairing DNA, RNA and protien. More surprisingly, they only inhabit environments typical of the extremes of early earth--hot springs, thermal ocean vents, saline lake, or oxygen deficient sediments. A breakpoint on the common evolutionary path, it is evident that the Archaea diverged early in the history of life, establishing thier importance in evolutionary sciences. Archaea: Ancient Microbes, Extreme Environments, and the Origin of Life tells this evolving story, furthering our understanding of the microbe commonalities, and providing for evolutionary justification in the use of archaea as mechanistic model systems. Key Features* Provides a unique and current summary of common subcellular mechanisms in archaea and eukaryotes* Emphasizes the use of genomics to provide a biological context for understanding archaea* Contrasts evolutionary studies on the fossil record with those on molecular phylogeny* Includes extensive tables, graphs, images, drawings and other illustrations* Simplifies the interdisciplinary challenge necessary to understand the significance of archaea
E-Book Content
PREFACE Biologists divide living organisms into prokaryotes, represented by the bacteria, and eukaryotes such as ourselves. In this scheme, bacteria are considered to be the most primitive form of life. One popular idea about how life arose supposes that humans evolved from bacteria. In this age of genomics, however, DNA sequence comparisons indicate that our genes are unlike those of bacteria. Where, then, did we come from? An answer to that question comes from a truly unexpected source, life in extreme environments. It was generally thought that boiling acid hot springs or saturating saline lakes were sterile, however, life is both present and highly successful. Many of the resident organisms are still microbes, just not bacteria. We call them archaea. Whole-genome DNA sequences of five archaeal species reveal remarkable gene matches to human genes and those of other eukaryotes. These matches occur in the most essential of the subcellular processes carried out by all organisms, the synthesis and repair of DNA, RNA, and protein. This suggests that eukaryotes evolved from archaea or perhaps that archaea and eukaryotes derive from a common ancestor. Gene sequences aside, archaea lay additional claim to the title of ancient organism based on geologic and taxonomic considerations. The early Earth (Archean age) was a time of elevated surface temperatures. Fossil dating indicates the presence of microbes at the close of this period, suggesting that earlier forms of life from which these fossils would have derived must have been adapted to temperature extremes. Microbes called hyperthermophiles with just these abilities are still found on the Earth in geothermal springs and hydrothermal ocean vents. These extreme locations exhibit geochemistries most like that of early Earth. To understand how such organisms relate to other forms of life, taxonomic methods based on ribosomal RNA sequences have been used to create phylogenetic “trees” of life. These hyperthermophilic microbes, dominated by the archaea, exhibit the deepest phylogenetic branches, suggesting that they have undergone the longest period of evolution among extant organisms. Taken together, these ideas suggest that hyperthermophilic archaea may represent a form of the earliest type of life. The intent of this book is to expand the general understanding of the archaea. As simple organisms with sequenced genomes, they present uniq