Archaea

4 Key excerpts on "Archaea"

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  eBook - ePub

  Microbiology For Dummies

  • Jennifer Stearns, Michael Surette(Authors)
  • 2019(Publication Date)
  • For Dummies

    (Publisher)

  Figure 12-7 . It’s likely that many more Archaea will be discovered and that the current tree will change quite a bit.

  FIGURE 12-7: The phylogenetic tree of Archaea.

  Currently, there are two main phyla in the domain Archaea: the Euryarchaeota and the Crenarchaeota. However, within the Crenarchaeota, there may soon be a few new phyla, including the Thaumarchaeota, the Korarchaeota, and the Aigarchaeota.

  As new Archaeal strains are discovered, the gaps in what we know about how all Archaea are related get filled in.

  WHERE DO MY GENES COME FROM?

  The Archaea are interesting because they have many genes that resemble those in bacteria and others that resemble the genes in eukaryotes. This is part of the reason why they confounded microbiologists for years — they couldn’t squarely be placed within the domain of Bacteria or Eukarya.

  A great example of this is an archaeon (singular for Archaea) called Methanocaldococcus jannaschii, which has core metabolic genes that bear some resemblance to those in bacteria, but most of the genes for molecular processes (things like RNA transcription and protein translation) have similarities to those in eukaryotes. More than a third of its genome (40 percent) contains genes that don’t resemble those in either bacteria or eukaryotes.

  Archaea likely evolved around the same time as the earliest bacteria. It’s even possible that eukaryotes came from an early Archaeal ancestor. It’s mysteries like this that make the microbiology of the Archaea so fascinating.

  As with the Bacteria, there are far too many Archaeal species to describe them all here but you can go to www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=2157 for a complete list. In this section, we discuss representatives of the different forms of Archaeal life, filling you in on their ability to tolerate extremes of temperature, acidity, and salinity. It’s likely that the most extreme of the Archaea were some of the first life forms on earth, evolving during a time when the earth was hotter and harsher than it is now. How they’re able to thrive in extreme conditions is covered in Chapter 11

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  Microbes

  Concepts and Applications

  • Prakash S. Bisen, Mousumi Debnath, G. B. Prasad(Authors)
  • 2012(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  halobacteria), a group of Archaea, require at least a 2 M salt concentration and are usually found in saturated solutions (about 36% w/v salts). These are the primary inhabitants of salt lakes, inland seas, and evaporating ponds of seawater, such as the Dead Sea and solar salterns, where they tint the water column and sediments bright colors. In other words, they will most likely perish if they are exposed to anything other than a very high concentration salt conditioned environment. These prokaryotes require salt for growth. The high concentration of NaCl in their environment limits the availability of oxygen for respiration. Their cellular machinery is adapted to high salt concentrations by having charged amino acids on their surfaces, allowing the retention of water molecules around these components. They are heterotrophs that normally respire by aerobic means. Most halophiles are unable to survive outside their high salt native environment. Indeed, many cells are so fragile that when placed in distilled water, they immediately lyse from the change in osmotic conditions.

  HaloArchaea, and particularly, the family Halobacteriaceae are members of the domain Archaea and comprise the majority of the prokaryotic population. There are currently 15 recognized genera in the family. The domain Bacteria (mainly Salinibacter ruber) can comprise up to 25% of the prokaryotic community but comprises more commonly a much lower percentage of the overall population.

  A comparatively wide range of taxa have been isolated from saltern crystallizer ponds, including members of the following genera: Haloferax, Halogeometricum, Halococcus, Haloterrigena, Halorubrum, Haloarcula, and Halobacterium (Oren, 2002). However, the viable counts in these cultivation studies have been small when compared to total counts, and the numerical significance of these isolates has been unclear. Only recently it has become possible to determine the identities and relative abundances of organisms in natural populations, typically using polymerase chain reaction (PCR)-based strategies that target 16S small subunit ribosomal ribonucleic acid (16S rRNA) genes. While comparatively few studies of this type have been performed, results from these suggest that some of the most readily isolated and studied genera may not in fact be significant in the in situ community. This is seen in cases such as the genus Haloarcula, which is estimated to make up less than 0.1% of the in situ community but commonly appears in isolation studies.

  5.6.2. Extreme Thermophiles

  A thermophile is a type of extremophilic organism that thrives at relatively high temperatures, between 45 and 80 °C (113 and 176 °F, respectively). Many thermophiles are Archaea. Extreme thermophiles are critters that live in some of the most unwelcoming environments on the planet. Archaea such as Sulfolobus acidocaldarius live in hot springs and geysers where the water temperature can be up to 100 °C and the water is filled with sulfuric acid (Fig. 5.24 ). Chlororflexus aurantiacus can carry out photosynthesis at over 60 °C. Pyrococcus furiosus

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  The New Microbiology

  From Microbiomes to CRISPR

  • Pascale Cossart(Author)
  • 2018(Publication Date)
  • ASM Press

    (Publisher)

  PART I New Concepts in Microbiology Passage contains an image

  CHAPTER 1 Bacteria: Many Friends, Few Enemies

  Bacteria are unicellular living organisms that make up one of the three domains of life: Bacteria, Archaea, and Eukaryota (Fig. 1 ). This model of three branches stemming from a common ancestor was first proposed by Carl Wo-ese in 1977. The absence of a nucleus is one major difference between prokaryotes and eukaryotes. Eukaryota or eukaryotes include animals, plants, fungi, and protozoa, which all have nuclei; bacteria and Archaea are prokaryotes and do not have a nucleus. The DNA of prokaryotes is non-membrane bound, unlike in eukaryotes. But do not assume that bacteria are merely small sacks full of disorderly contents. Their “interior” is in fact very well organized.

  Archaea, like bacteria, are unicellular organisms but differ from bacteria in that they have lipids that are not found in bacteria and an ensemble of compounds that are similar to those of eukaryotes, in particular the machinery that regulates gene expression. When they were discovered, Archaea were thought to exist only in extreme environments, such as very hot water springs, but we now know that they are present everywhere, including in our gut.

  Figure 1.

  The three large domains of life. Bacteria, Archaea, and Eukaryota have a common ancestor.

  Bacteria are extremely varied and make up the most diverse domain of life. They have been on Earth for billions of years and have evolved to survive in a great variety of conditions. There are more than 11,500 known species of bacteria in more than 2,000 genera (groupings of species). These numbers have so far been based only on gene comparisons, particularly the 16S RNA genes, and they keep rising. Classification methods are changing too. Now that we can compare entire genome sequences, the definition of “species” itself is evolving.

  Bacteria may have different shapes (Fig. 2 ). There are four main categories: cocci, or spheres; bacilli, or rods; spirals; and comma-shaped, or curved bacteria. All bacteria divide, regardless of their shape. One bacterium splits into two, via an asexual reproduction. Nevertheless, genetic material can be exchanged between two bacteria by means of mechanisms described as horizontal gene transfer

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  eBook - ePub

  Microbial Ecology

  • Larry L. Barton, Diana E. Northup(Authors)
  • 2011(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Chapter 1 Microbial Ecology: Beginnings and the Road Forward 1.1 Central Themes Interdisciplinary studies addressing the origin and evolution of life stimulate many ongoing conversations and research activities. Prokaryote classification is based on biochemical and physiological activities as well as structures including cell morphology. Classification within Bacteria and Archaea domains is complicated because the definition for a prokaryotic species is currently under review. Our knowledge of the microbial diversity of Earth is growing exponentially with the discovery and implementation of molecular phylogeny to study environmental microbiology. Configuration of the “tree of life” has changed since the 1990s with the use of molecular and genomic techniques to evaluate microbial relationships. Microbial ecology as a discipline will benefit substantially from the development of a theoretical basis that draws on principles identified in general ecology. 1.2 Introduction The study of microbial ecology encompasses topics ranging from individual cells to complex systems and includes many different microbial types. Not only is there a visual difference in examining pure cultures and unique microbial environments (see Figure 1.1), but also there is a difference in study approach in each of these images. Microbial ecology has benefited from studies by scientists from many different scientific fields addressing environments throughout the globe. At this time there is considerable interest in understanding microbial community structure in the environment. To achieve this understanding, it is necessary to identify microbes present; this can be accomplished by using molecular methods even though the microbes have not been cultivated in the laboratory

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