Archaea: Diversity and Characteristics

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Questions and Answers

Which of the following best describes haloarchaea?

They are primarily anaerobic microorganisms.

They reproduce by binary fission and do not form spores. (correct)

They have a thick peptidoglycan cell wall.

They are primarily found in freshwater environments.

Which eukaryotic organism is identified as a significant oxygenic phototroph in salt lakes?

Dunaliella (correct)

Thermoplasma

Ectothiorhodospira

Halorhodospira

What is a characteristic feature of extreme halophiles?

They reproduce through budding.

They are obligate aerobes and do not possess gas vesicles.

Few strains are weakly motile by archaella. (correct)

They thrive at acidic pH levels above 5.

Which microorganism is capable of thriving at a pH below 0?

Picrophilus Signup and view all the answers

Why are artificial saline habitats significant for the study of extremophiles?

They can provide unique insights into salt preferences of certain microbial species. Signup and view all the answers

What is the primary ecological role of methanogens?

They are key contributors to methane production in anoxic conditions. Signup and view all the answers

At what temperature can Methanopyrus grow rapidly, making it a unique hyperthermophilic methanogen?

100 degrees C Signup and view all the answers

Which group of Archaea includes organisms that require high concentrations of sodium chloride for growth?

Extreme halophiles Signup and view all the answers

Which feature distinguishes methanogens from extreme halophiles within the Euryarchaeota phylum?

Methanogens are strict anaerobes while extreme halophiles are primarily obligate aerobes. Signup and view all the answers

What is the maximum NaCl concentration at which some extreme halophiles can survive?

5.5 M NaCl Signup and view all the answers

Which of the following is NOT a characteristic of hyperthermophiles?

They require high levels of sodium chloride for growth. Signup and view all the answers

Methanopyrus, the hyperthermophilic methanogen, produces methane using which substrates?

Hydrogen and carbon dioxide Signup and view all the answers

Which of the following correctly classifies the Euryarchaeota with respect to their nutritional modes?

Both aerobic and anaerobic organisms with varying metabolic processes Signup and view all the answers

Which phylum do all well-characterized methanogens belong to?

Euryarchaeota Signup and view all the answers

What characteristic is unique to Archaea and refers specifically to their methane production?

Methanogenesis Signup and view all the answers

Which superphyla includes the phyla Diapherotrites and Nanohaloarchaeota?

DPANN Signup and view all the answers

Which of the following features are commonly found in Archaea?

Ether-linked lipids Signup and view all the answers

What is the significance of the superphyla classification in relation to archaeal diversity?

It helps cluster various archaeal phyla into larger taxonomic groups Signup and view all the answers

Which of the following is NOT a recognized archaeal superphyla?

Euryarchaeota Signup and view all the answers

Archaea are able to use a wide diversity of what in their metabolism?

Electron donors and acceptors Signup and view all the answers

What is a notable environment where many Archaea are found?

Volcanic systems Signup and view all the answers

Study Notes

Domain Archaea

Archaea are named for the Archaean eon, the period of geological history when life first spread across Earth
During the Archaean, Earth was enveloped by high temperatures and an atmosphere lacking oxygen but with toxic gases
Archaea were once considered remnants of this early era, as many live in extreme environments such as volcanic systems and salt ponds
Archaea are single-celled organisms with prokaryotic cell structure, but are genetically and physiologically distinct from Bacteria
They share more features with Eukarya
Archaeal cells likely contributed to the origin of Eukarya

Diversity and Cultivation

Archaea are nearly as diverse as Bacteria, although many are difficult to cultivate
Most well-characterized Archaea come from only two phyla: Euryarchaeota and Crenarchaeota
Several species have also been isolated from the phylum Thaumarchaeota
Korarchaeota and Nanoarchaeota are represented only by strains grown in cocultures or by enrichment techniques

Phylogenetic Relationships

A phylogenetic tree (Figure 17.1) shows the relationships between major archaeal orders within the five major archaeal phyla (studied in pure or highly enriched cultures) and other archaeal taxa
There are four major branches: Euryarchaeota, DPANN, TACK, and Asgard. The exact position of the root of the archaeal tree remains uncertain.

Common Traits

Common traits of Archaea include ether-linked lipids, a lack of peptidoglycan in cell walls, and structurally complex RNA polymerases similar to those of Eukarya
Archaea can be chemoorganotrophs or chemolithotrophs, and they can be respiratory or fermentative, aerobic, or anaerobic, using diverse electron donors and acceptors

Superphyla

Broader taxonomic sampling has led to the clustering of archaeal phyla into superphyla
Currently, three named superphyla are recognized: Asgard, DPANN, and TACK
DPANN and TACK are named based on the phyla present within them

Unusual Characteristics of Archaea

Methane production (methanogenesis) is a unique characteristic of Archaea, called methanogens
Methanogenesis evolved early in archaeal evolution, with well-characterized methanogens belonging to the phylum Euryarchaeota
Methanogenesis is globally important as it produces most natural gas and significantly affects climate due to methane's "greenhouse gas" effect
Methanogens are important in various anoxic environments such as freshwater sediments, wetlands, rice paddies, wastewater treatment plants, geothermal systems, and within animal guts

Hyperthermophilic Methanogens

Methanopyrus, a hyperthermophilic methanogen, is a rod-shaped organism that shares properties with both hyperthermophiles and methanogens
It was isolated from hot sediments near submarine hydrothermal vents and from "black smoker" hydrothermal vent chimneys
This organism produces methane only from hydrogen and carbon dioxide, and grows rapidly at high temperatures

Extremophiles

Archaea include many examples of extremophiles, including hyperthermophiles (growth optimized above 80°C), halophiles, acidophiles, and psychrophiles
These organisms live in extreme environments

Halophilic Archaea

Extremely halophilic Archaea (haloarchaea) live in environments with high salt concentrations
These environments include naturally salty environments, solar salt evaporation ponds, marine salterns, and artificial saline habitats like heavily salted foods

Other Microorganisms in Salt Environments

Eukaryotic algae, such as Dunaliella, are often the dominant oxygenic phototrophs in salt lakes
In highly alkaline soda lakes, anoxygenic phototrophic purple bacteria like Ectothiorhodospira and Halorhodospira dominate

Additional Characteristics

Haloarchaea stain gram-negative, reproduce by binary fission, and do not form spores
Cells can be rod-shaped, cocci, cup-shaped, or even square-shaped, and some contain gas vesicles
Some strains of extreme halophiles are weakly motile, while most lack archaella

Acidophilic and Thermophilic Examples

Other Archaea, such as Thermoplasma, Ferroplasma, and Picrophilus, are thermophilic and acidophilic
Some of these organisms show the capability of growth below pH 0, in acidic conditions
Thermoplasma and Ferroplasma are cell wall-less

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Description

Explore the fascinating domain of Archaea, organisms that emerged during the Archaean eon when life first spread across Earth. Learn about their unique characteristics, extreme environments, and the diversity within this group. Discover their relationships with Bacteria and Eukarya, and how they contribute to our understanding of life's origins.