20 Notes - Topic 20 Fundamentals of...

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Unformatted text preview: Topic 20 Fundamentals of Microbiology (Biology 140) Course notes Dr. Josh D. Neufeld Learning Objectives: To explore the diversity of the Archaea, beginning with the Euryarchaeota. The Archaea have long been recognized as being structurally and physiologically distinct from the Bacteria (review Tables 16.1), and now it has been shown that they are indeed phylogenetically distinct from the Bacteria. Perhaps because Archaea are not known to cause diseases of animals or plants, they have not been studied as intensively as have some of the Bacteria. However, with modern molecular methods, we are now finding Archaea (many of them newly ­described organisms) in places where they were not known previously. It is clear that they play important roles in the environment, and some of them do live in association with animals and other eukaryotic organisms. So far, the domain Archaea has been divided into two phyla (Figure 19.1), the Euryarchaeota and the Crenarchaeota. Some of the branches of the Archaeal phylogenetic tree, such as the Marine Euryarchaeota, the Marine Crenarchaeota, and the entire Korarchaeota kingdom, are represented almost entirely by genetic material isolated from environmental samples – very few organisms have yet been cultured. Euryarchaetoa Extremely Halophilic Archaea (Table 19.2) • Require very high salt concentration environment (Table 19.1), at least 1.5 M NaCl (~9%). • Can grow at 5.5 M NaCl (saturated) • Chemoorganotrophs, obligate aerobes • Halobacterium has been most extensively studied • Require sodium ions specifically; help to stabilize the glycoprotein cell wall, which contains acidic amino acids • Use potassium as compatible solute inside the cell (Table 19.3) • Cytoplasmic proteins require high concentration of potassium ions for stability • Fundamentals of Microbiology (Biology 140) Course notes Dr. Josh D. Neufeld Under low O2 conditions, some can use light to generate ATP, using the protein bacteriorhodopsin and the carotenoid pigment retinal (Figure 19.4) which work together to set up a proton gradient across the cell membrane Methanogens (Table 19.5) • Obligate anaerobes, usually mesophilic • Phylogenetically diverse • Range of habitats (Table 19.4) • A relatively narrow range of substrates can be converted to methane (Table 19.6) in energy yielding reactions Thermoplasmatales • Thermophilic (optimum 55°C) usually (Ferroplasma is not), extremely acidophilic, chemoorganotrophs, facultative • Phylogenetically related • Thermoplasma and lacks cell walls; cytoplasmic membrane has chemically unique structure (Figure 19.11) • Picrophilus can grow below pH 0, optimum pH 0.7 Thermococcales and Methanopyrus • Hyperthermophiles (optimum >80ºC) o Thermococcus grows from 70 ­95°C o Pyrococcus grows from 70 ­106°C • Obligately anaerobic chemoorganotrophs • Use S° as terminal electron acceptor, reducing to H2S • Motile, tuft of flagella • Methanopyrus may be one of least ­derived microbes known. It appears to lie near the base of the archaeal tree (Figure 19.1) o hyperthermophilic rather than mesophilic (as most known methanogens are); possesses an unusual tetraether ­linked membrane lipid Archaeoglobales Fundamentals of Microbiology (Biology 140) Course notes Dr. Josh D. Neufeld • From hot marine sediments, near hydrothermal vents • Oxidation of H2 or organic compounds coupled to reduction of sulfate to sulfide • Irregular cocci, optimal growth ~80°C ...
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