What are Archaea?
We have learned that Biology can be illustrated as a tree of life:
In this tree of life, one of the basal branches evolves into a group of organisms that is part of Domain Prokarya, and is the current extant Kingdom Archaea. Archaebacteria is a synonym used by some authors for the kingdom of the archaea.
Prior to 1977 the archaea were considered to be just another group of bacteria, so archaea were first part of Kingdom Plantae (green) when there were only two kingdoms. archaea followed the bacteria as fellow prokaryotes into the new kingdom, Monera (yellow) in the 3 to 5 kingdom era. In 1977 Carl Woese and George Fox proposed that archaea are different enough to have their own kingdom. In 1990 16S rRNA and 18S rRNA sequences for the archaea were found different enough from the other bacteria to justify this. By 2003, the genome sequence analysis results confirmed that archaea are really quite different from bacteria. The archaea were therefore split out from Monera in the transition to 6 kingdoms, and the kingdom was named Archaea.
The archaea have ancient origin, just like the bacteria, but they are somewhat more advanced in certain features. A chief example of these features is that the circular DNA molecule is associated with DNA binding proteins. These are not the histones of eukaryotes, but they are somewhat similar. Bacteria as you recall lack DNA binding proteins. So archaea are somewhere between bacteria and eukaryotes in this regard. So as you noticed in the phylogeny above, the archaea branch on the tree of life is between bacteria and eukaryotes. These organisms have had a long time to evolve and diversify into cells with a wide range of forms and functions.
The archaea can be categorized as being extremophiles, meaning that they are found today in some of the most extreme environments on earth. They live in water that is 90°C (nearly boiling), -4°C (nearly freezing) pH 2 (highly acidic), 25M (very salty), or anaerobic conditions.
We have learned that Biology can be illustrated as a tree of life:
In this tree of life, one of the basal branches evolves into a group of organisms that is part of Domain Prokarya, and is the current extant Kingdom Archaea. Archaebacteria is a synonym used by some authors for the kingdom of the archaea.
Prior to 1977 the archaea were considered to be just another group of bacteria, so archaea were first part of Kingdom Plantae (green) when there were only two kingdoms. archaea followed the bacteria as fellow prokaryotes into the new kingdom, Monera (yellow) in the 3 to 5 kingdom era. In 1977 Carl Woese and George Fox proposed that archaea are different enough to have their own kingdom. In 1990 16S rRNA and 18S rRNA sequences for the archaea were found different enough from the other bacteria to justify this. By 2003, the genome sequence analysis results confirmed that archaea are really quite different from bacteria. The archaea were therefore split out from Monera in the transition to 6 kingdoms, and the kingdom was named Archaea.
The archaea have ancient origin, just like the bacteria, but they are somewhat more advanced in certain features. A chief example of these features is that the circular DNA molecule is associated with DNA binding proteins. These are not the histones of eukaryotes, but they are somewhat similar. Bacteria as you recall lack DNA binding proteins. So archaea are somewhere between bacteria and eukaryotes in this regard. So as you noticed in the phylogeny above, the archaea branch on the tree of life is between bacteria and eukaryotes. These organisms have had a long time to evolve and diversify into cells with a wide range of forms and functions.
The archaea can be categorized as being extremophiles, meaning that they are found today in some of the most extreme environments on earth. They live in water that is 90°C (nearly boiling), -4°C (nearly freezing) pH 2 (highly acidic), 25M (very salty), or anaerobic conditions.
Archaea Cellular Structure
Archaea evolved many cell sizes, but all are relatively small. The thermoplasmas are the smallest of the archaea. Most archaea fall into size classes (0.1 to 15 μ diameter and up to 200 μ long) matching bacteria. So they are about the size of a mitochondrion in a eukaryotic cell.
Archaea have also evolved into many cell shapes similar to those of bacteria. There are bacilli, cocci, spirilli, and plate-like forms of archaea.
Also like bacteria, the cells of archaea form various associations within a population of cells. Some species are unicellular, others are colonial, and yet others are filamentous.
Just like bacterial cells, archaea cells come in three basic forms in terms of the cell boundary.
Mycoplasma-like Thermoplasma cells lack a cell wall. They have a cell membrane bilayer, but it is made of phosphoglycohydrocarbons, or sulfo- or glyco-glycerohydrocarbons. What would be a fatty acid in our cells, is a hydrocarbon in archaea, so they are liked by an ether link rather than the ester linkage to the glycerol. This membrane has transport proteins that regulate what goes into and out of the cell. Without any wall, these cells are forced to live isotonic environments rather than in, say, freshwater environments.
Other species of archaea, such as Methanobacterium are Gram positive because they retain the purple dye-iodine complex inside the thick cell wall after the Gram staining process. The differences between these and the Gram positive bacteria include the fact that the wall material is a glycan...not a peptidoglycan. There is no muramic acid here...so no murein. This rigid wall is what allows these archaea to live in a hypotonic environment without bursting.
A third group of archaea, including Thermoproteus, are Gram negative. These cells typically have only a very thin surface layer of glycan wall which may include glycoproteins. So the purple dye-iodine complex inside the cell rinses right out with the alcohol rinse. So these archaea appear pink rather than purple after the Gram staining procedure.
Kingdom Archaea can be divided into two major phyla. The Euarchaeota phylum contains those archaea that are halophilic (Halobacteriales) meaning that they live in very concentrated salt solutions...brine. When our biology students visit the Bahamas this spring, they will canoe on and snorkel in some of the hypersaline lakes on the interior of San Salvador Island. These lakes are often streaked with orange, red, and purple colors by the halophilic archaea that live there. These are chemoheterotrophs that respire with oxygen, and chemoautotrophs that may use bacteriorhodopsin to harvest light energy to make ATP.
Phylum Euarchaeota also includes methanogens (Methanogenales). These anaerobic archaea convert carbon dioxide and hydrogen to methane (CH4), known as swamp gas or natural gas. Some of these organisms use a fluorescent pigment for energy to drive this reaction. Some of these species indeed live in swamps, marshes, and landfills. Others live in the gut of ruminant animals who then belch quantities of methane into the atmosphere.
Phylum Euarcheota as well includes thermophiles (Thermoplasmales, Thermococcales, and Archaeoglobales). These organisms live in hot water in geothermal features (geysers, paint pots, hot springs, mud pots, etc.). Some of these are chemoheterotrophs that use inorganic chemicals for energy (converting sulfur to hydrogen sulfide gas Phew!) to convert larger organic molecules to carbon dioxide. Other species in this group are autotrophic, converting sulfates in the geothermal features to hydrogen sulfide gas (again, Phew!) Some of archaea in these groups live near hydrothermal vents...and convert methane gas backwards into lactate, and then from there to hydrogen gas and carbon dioxide.
The second phylum of Kingdom Archaea is Crenarchaeota. Most of the organisms in this phylum are also thermophilic, but also most are acidophilic. So they live in very acidic hot water environments. This would be corrosive conditions. Some are autotrophic and use carbon dioxide. Others convert sulfur and hydrogen to hydrogen sulfide gas and more acid! In the absence of oxygen, heterotrophic crenarchaeotes use organic molecules and sulfur to make carbon dioxide and hydrogen sulfide gas. More stinkers! These same crenarchaeotes in the presence of oxygen will process organic molecules by running the TCA cycle backwards to convert sulfur and oxygen into sulfuric acid (H2SO4), otherwise known as battery acid. Obviously these are some organisms that can live in and help maintain some extreme environments.
Archaea evolved many cell sizes, but all are relatively small. The thermoplasmas are the smallest of the archaea. Most archaea fall into size classes (0.1 to 15 μ diameter and up to 200 μ long) matching bacteria. So they are about the size of a mitochondrion in a eukaryotic cell.
Archaea have also evolved into many cell shapes similar to those of bacteria. There are bacilli, cocci, spirilli, and plate-like forms of archaea.
Also like bacteria, the cells of archaea form various associations within a population of cells. Some species are unicellular, others are colonial, and yet others are filamentous.
Just like bacterial cells, archaea cells come in three basic forms in terms of the cell boundary.
Mycoplasma-like Thermoplasma cells lack a cell wall. They have a cell membrane bilayer, but it is made of phosphoglycohydrocarbons, or sulfo- or glyco-glycerohydrocarbons. What would be a fatty acid in our cells, is a hydrocarbon in archaea, so they are liked by an ether link rather than the ester linkage to the glycerol. This membrane has transport proteins that regulate what goes into and out of the cell. Without any wall, these cells are forced to live isotonic environments rather than in, say, freshwater environments.
Other species of archaea, such as Methanobacterium are Gram positive because they retain the purple dye-iodine complex inside the thick cell wall after the Gram staining process. The differences between these and the Gram positive bacteria include the fact that the wall material is a glycan...not a peptidoglycan. There is no muramic acid here...so no murein. This rigid wall is what allows these archaea to live in a hypotonic environment without bursting.
A third group of archaea, including Thermoproteus, are Gram negative. These cells typically have only a very thin surface layer of glycan wall which may include glycoproteins. So the purple dye-iodine complex inside the cell rinses right out with the alcohol rinse. So these archaea appear pink rather than purple after the Gram staining procedure.
Kingdom Archaea can be divided into two major phyla. The Euarchaeota phylum contains those archaea that are halophilic (Halobacteriales) meaning that they live in very concentrated salt solutions...brine. When our biology students visit the Bahamas this spring, they will canoe on and snorkel in some of the hypersaline lakes on the interior of San Salvador Island. These lakes are often streaked with orange, red, and purple colors by the halophilic archaea that live there. These are chemoheterotrophs that respire with oxygen, and chemoautotrophs that may use bacteriorhodopsin to harvest light energy to make ATP.
Phylum Euarchaeota also includes methanogens (Methanogenales). These anaerobic archaea convert carbon dioxide and hydrogen to methane (CH4), known as swamp gas or natural gas. Some of these organisms use a fluorescent pigment for energy to drive this reaction. Some of these species indeed live in swamps, marshes, and landfills. Others live in the gut of ruminant animals who then belch quantities of methane into the atmosphere.
Phylum Euarcheota as well includes thermophiles (Thermoplasmales, Thermococcales, and Archaeoglobales). These organisms live in hot water in geothermal features (geysers, paint pots, hot springs, mud pots, etc.). Some of these are chemoheterotrophs that use inorganic chemicals for energy (converting sulfur to hydrogen sulfide gas Phew!) to convert larger organic molecules to carbon dioxide. Other species in this group are autotrophic, converting sulfates in the geothermal features to hydrogen sulfide gas (again, Phew!) Some of archaea in these groups live near hydrothermal vents...and convert methane gas backwards into lactate, and then from there to hydrogen gas and carbon dioxide.
The second phylum of Kingdom Archaea is Crenarchaeota. Most of the organisms in this phylum are also thermophilic, but also most are acidophilic. So they live in very acidic hot water environments. This would be corrosive conditions. Some are autotrophic and use carbon dioxide. Others convert sulfur and hydrogen to hydrogen sulfide gas and more acid! In the absence of oxygen, heterotrophic crenarchaeotes use organic molecules and sulfur to make carbon dioxide and hydrogen sulfide gas. More stinkers! These same crenarchaeotes in the presence of oxygen will process organic molecules by running the TCA cycle backwards to convert sulfur and oxygen into sulfuric acid (H2SO4), otherwise known as battery acid. Obviously these are some organisms that can live in and help maintain some extreme environments.
Credits to the owner: Koning, Ross E. 1994. Kingdom Archaea. Plant Physiology Information Website. http://plantphys.info/organismal/lechtml/archaea.shtml. (4-29-2014).