7.8B: Shared Features of Bacteria and Archaea
Most of the metabolic pathways, which comprise the majority of an organism’s genes, are common between Archaea and Bacteria.
LEARNING OBJECTIVES
Describe the evidence for the evolution of the Archaea from Bacteria
Key Takeaways
The relationship between the three domains is of central importance for understanding the origin of life. Most of the metabolic pathways, which comprise the majority of an organism ‘s genes, are common between Archaea and Bacteria, while most genes involved in genome expression are common between Archaea and Eukarya. Within prokaryotes, archaeal cell structure is most similar to that of Gram-positive bacteria, largely because both have a single lipid bilayer and usually contain a thick sacculus of varying chemical composition. In phylogenetic trees based upon different gene/ protein sequences of prokaryotic homologs, the archaeal homologs are more closely related to those of Gram-positive bacteria. Archaea and Gram-positive bacteria also share conserved indels in a number of important proteins, such as Hsp70 and glutamine synthetase I.
R.S. Gupta has proposed that the Archaea evolved from Gram-positive bacteria in response to antibiotic selection pressure. This is suggested by the observation that archaea are resistant to a wide variety of antibiotics that are primarily produced by Gram-positive bacteria, and that these antibiotics primarily act on the genes that distinguish Archaea from Bacteria. His proposal is that the selective pressure towards resistance generated by the Gram-positive antibiotics was eventually sufficient to cause extensive changes in many of the antibiotics’ target genes, and that these strains represented the common ancestors of present-day Archaea. The evolution of Archaea in response to antibiotic selection, or any other competitive selective pressure, could also explain their adaptation to extreme environments (such as high temperature or acidity) as the result of a search for unoccupied niches to escape from antibiotic-producing organisms; Cavalier-Smith has made a similar suggestion. Gupta’s proposal is also supported by other work investigating protein structural relationships and studies that suggest that Gram-positive bacteria may constitute the earliest branching lineages within the prokaryotes.
Key Points
- Within prokaryotes, archaeal cell structure is most similar to that of Gram-positive bacteria, largely because both have a single lipid bilayer and usually contain a thick sacculus of varying chemical composition.
- It has been proposed that the Archaea evolved from Gram-positive bacteria in response to antibiotic selection pressure.
- The evolution of Archaea in response to antibiotic selection, or any other competitive selective pressure, could also explain their adaptation to extreme environments (such as high temperature or acidity).
Key Terms
- prokaryotes : ( /proʊkæri.oʊts/, pro-kah-ree-otes or /proʊkæriəts/, pro-kah-ree-əts) a group of organisms whose cells lack a cell nucleus (karyon), or any other membrane-bound organelles. Most prokaryotes are unicellular organisms, although a few such as myxobacteria have multicellular stages in their life cycles.
- archaea : a taxonomic domain of single-celled organisms lacking nuclei that are fundamentally from bacteria.
- bacteria : Bacteria constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most habitats on the planet.