Saran's Learn Microbiology

  VIRUSES OF ARCHAEA ·        Viruses of Archaea represent one of the most enigmatic parts of the Virosphere. ·        A virus infecting Archaea was first described in 1974. ·    Viruses are among the most abundant biological entities on earth, outnumbering cells in some environments by more than an order of magnitude. Viruses of Archaea (termed Archaeal viruses) are some of the most unusual and least understood group of viruses. ·        Most of the characterized Archaeal viruses infect Extremophilic hosts and display remarkable diversity of Virion morphotypes, many of which have never been observed among Viruses of bacteria or Eukaryotes. ·        Morphology - Most of the Archaeal viruses have Head-tail morphologies and Linear double-stranded DNA genomes. Other morphologies have also been described including Spindle shaped, Rod shaped, Filam...

  ·       The Archaellum (Archaeal flagellum) is a unique, ‘Tail-like’ structure used for Motility. ·        The Archaeal flagellum is thinner (10 - 15 nm) in size. ·      Like bacteria, the structure of the flagellum can be divided into three distinct components: (i) The filament, ii) Hook and iii) Anchoring structure. Each of these components is constructed of specific proteins either encoded by genes residing within flagellar operons or of currently unknown genes. ·     The Archaeal flagellum filament is assembled from Archaellin sub-units, which are N-glycosylated proteins. ·       Flagellation occurs in all the main groupings of the archaea, including Halophiles, Methanogens, Sulfur-dependent thermophiles and Hyperthermophiles. ·        Archaea use the motility apparatus Archaeal flagellum in combination with Chemotaxis systems to bia...

  ARCHAEAL CELL MEMBRANE ·        The Cytoplasmic membrane of Archaea is formed from either Glycerol diethers, which have 20 carbon side chains, or diglycerol tetraethers, which have 40 carbon side chains. ·      In the Tetraether lipid, the ends of the phytanyl side chains that point inward from each glycerol molecule are covalently linked. This forms a Lipid monolayer instead of a Lipid bilayer membrane. ·     In contrast to Lipid bilayers, Lipid monolayer membranes are extremely resistant to heat and are therefore widely distributed among Hyperthermophilic Archaea (organisms that grow best at temperatures above 80 °C). ·     Membranes with a mixture of bilayer and monolayer character are also possible, with some of the opposing hydrophobic groups covalently bonded and others not. Difference between Bacterial and Archaeal Cell membrane ·        There are several ch...