Archaea (annotation) L1 PDF

Unit 2 Section: E Microbial Physiology Growth yield and characteristics strategies of cell division stress response Archaea Group of (primitive) bacteria Living in extreme aquatic and terrestrial environments. Either gram positive or gram negative Spherical, rod-shaped, spir...

Unit 2 Section: E Microbial Physiology Growth yield and characteristics strategies of cell division stress response Archaea Group of (primitive) bacteria Living in extreme aquatic and terrestrial environments. Either gram positive or gram negative Spherical, rod-shaped, spiral, plate-shaped, or pleomorphic. Can be single cells, filaments or aggregates. Diameter range: 0.1 to 15 μm Some filaments can grow up to 200 μm in length. Multiplication may be by binary fission, budding, or fragmentation. Five-kingdom system Prokaryotes were classified based on phenotypic traits. This involved measuring various characteristics, including morphology, biochemistry, and growth abilities. Bacteria Archea  Carl Woese proposed : the six kingdoms & three domains based on ribosomal RNA data. The 16S ribosomal RNA (rRNA) gene is pivotal for prokaryotic phylogeny. Present in all cells, it is around 1500 bases long. Eukarya domain: Eukaryotic kingdoms (protista, fungi, plantae, animalia) were grouped into the. THREE DOMAINS SYSTEM Monera kingdom: split into: I. Eubacteria (bacteria) domains II. Archaea (archaebacteria) domains Woese's system, organizes biodiversity based on evolutionary relationships. Domains The 16S rRNA gene (1500 bases long) The gene features conserved regions for sequence alignment and variable/hypervariable regions for discriminating between organisms.  Euryarchaeota Archaeal Taxonomy Based on the rRNA data Crenarchaeota 1. Methanogenic archaea Archaeal Taxonomy 2. Archaea sulfate reducers Based on morphology and 3. Extremely halophilic archaea physiology 4. Cell wall–less archaea 5. Extremely thermophilic  Archaeal Taxonomy Based on the rRNA data Euryarchaeota Crenarchaeota Extreme hyperthermophiles (105°C ) 7 classes: This phylum contains 69 genera 1. Methanobacteria 2. Methanococci 2 Most studied genera are: 3. Halobacteria Thermoproteus 4. Thermoplasmata Sulfolobus 5. Thermococci 6. Archaeglobi Thermoproteus: Strict anaerobe, (T= 70 to 7. Methanopyri 97°C )and (pH 2.5 and 6.5). hot springs and other hot aquatic habitats rich in 9 orders sulfur. 15 families Sulfolobus: Aerobic, (T= 70 to 80°C ) and (pH 2 to 3). Archea Cell wall Archea have an ordered surface covering called an S-layer. S-Layer The S-layer has a regular geometric pattern something like floor tiles and is composed of protein or glycoprotein. Their biological roles include protecting the cell against: Ion and pH fluctuations, Osmotic stress, enzymes, lysozymes or predators. The S-layer also helps maintain the shape and envelope rigidity cells Archea Cell wall  Archea Cell wall (1) The most common envelope is a simple S-layer. (2) Some S-layers are covered with an additional protein sheath or a carbohydrate layer. (3) Other archaea have a carbohydrate layer beneath the S-layer or in place of an S-layer (4) Carbohydrate layer in place of an S-layer (5) A few have a double membrane Archea Cell wall Some methanogens have cell walls containing Pseudomurein Pseudomurine = N-acetyl-D-glucosamine (NAG) and N-acetyl-D-talosaminuronic acid (NAT) NAG & NAT linked by: β(1→3) glycosidic bonds S-layer Pseudomurein Cytoplasmic membrane These differences mean that lysozyme, penicillin, and other chemicals that affect peptidoglycan structure and synthesis in bacterial cell walls have no effect on archaeal cell walls. Pseudomurein (Archea: Methanogens) Peptidoglycan/ Murein (Bacteria) Plasma membranes 5C Isoprene (branched) Plasma membranes Archaeal tetraether monolayer Phospholipid bilayer of bacteria and eukaryotes Comparison of Plasma Membrane Lipid Between Bacteria and Archaea. Phytanyl side chains are branched isoprenoid chains. Isoprenoid side chains are lipid compounds Plasma membranes Characteristic Archea Eubacteria Chirality of the glycerol linkage L-isomeric form D-isomeric form Linkage b/w the glycerol and side chain Ether-linkage Ester-linked lipids (more chemical stability to the membrane) Fatty acids Branched chain fatty acids Unbranched fatty acids (Highly-methylated Isoprenoid chains) Archaeal lipids Isopranyl glycerol ethers Usual glycerol fatty acid esters Plasma membrane Diether bilayer Phospholipid bilayer Tetraether Monolayer  How do ether bonds contribute to the thermal resistance of archaeal membranes? Ether bonds increase the stability of the cell membrane against hydrolysis at high temperatures. Here are some other differences between ether and ester bonds: Properties Ester Bonds Ether Bonds Chemical properties more prone to chemical reactions Less prone to chemical reactions Structure Ester groups require 2 oxygen atoms & 2 1 oxygen atom & 2 carbon atoms carbon atoms Hydrogen bonds cannot form H bonds can form H bonds Polarity C-O bond in esters is more polar, easier to C-O bond in ethers is less polar, difficult break to break Strength Generally stronger than ether bonds Less stronger than ester bonds Stability Less stable More stable than esters Solubility More polar and soluble in water Less polar Plasma membranes 20C in length Less rigid Tetraethers are formed from saturated diethers through a head-to-head condensation reaction. 40C in length More rigid  Archaea adjust the degree of tetraether lipid cyclization in order to maintain functional membranes and cellular homeostasis when confronted with pH and/or thermal stress. Cells can adjust the overall length of the tetraethers by cyclizing the chains to form pentacyclic rings Molecules 1, 2, and 3 Molecules 4, 5, and Molecule 5 and 6 are are bacterial lipids 6 are archaeal lipids. diglycerol tetraethers.  Bacteria Vs Archaebacteria Property Bacteria Archaea Plasma membrane lipids Ester-linked phospholipids and hopanoids form a Glycerol diethers form lipid bilayers; glycerol lipid bilayer; some have sterols tetraethers form lipid monolayers Cell wall constituents Peptidoglycan is present in nearly all; some lack Very diverse some consist of S-layer only, others cell walls combine S-layer with polysaccharides or proteins or both; some lack cell walls Inclusions bodies Yes, including gas vacuoles Yes, including gas vacuoles Ribosome size 70S 70S Chromosome structure Most are circular, double-stranded (ds) DNA; All known are circular, dsDNA usually a single chromosome Plasmids present Yes; circular and linear dsDNA Yes; circular dsDNA External structures Flagella, fimbriae (pili) common Flagella, pili, and pilus like structures common Capsules or slime layers Common Rare  Difference between bacteria and archaea Property Bacteria (Eubacteria) Archea (Archaebacteria) Nucleus Absent Absent Membrane bound organelles Absent Absent Cell wall Peptidoglycan containing muramic acid Variety of types, no muramic acid Membrane lipid Have ester-linked, straight chained fatty acid Have ether-linked, branched aliphatic chains Transfer RNA Thymine present; N- Formylmethionine carried by No thymine in T or TψC arm initiator tRNA Methionine carried by initiator tRNA Ribosomes Elongation factor 2 Does not react with diphtheria toxin Reacts Sensitivity to chloramphenicol Sensitive Insensitive Sensitivity to anisomycin Insensitive Sensitive DNA dependent RNA Polymerase Number of enzymes One Several Rifampicin sensitivity Sensitive Insensitive Polymerase II Type Promters Absent Present Metabolism Methanogenesis Absent Present Chlorophyll-based photosynthesis Present Absent (CSIR NET LIFE SCIENCES Dec 2014) Q. Which of the following statements best describe archaebacteria? A. Mostly autotrophic, cell wall contains peptidoglycan, 60S ribosomes, live in extreme environment. B. Divide by fission, not susceptible to lysozyme, live in extreme environments, mostly autotropic. C. Not susceptible to lysozyme, contain Golgi and linear chromosomes. D. Chitinous cell wall, obligate aerobic, circular chromosomes. Explanation Ans: b - Archaebacteria divide by binary fission, similar to bacteria. - They are not susceptible to lysozyme, which is an enzyme that can break down bacterial cell walls. - Archaebacteria are known to inhabit extreme environments such as hot springs, salt lakes. - While some archaebacteria are autotrophic, meaning they can produce their own food, not all of them are strictly autotrophic. (CSIR NET LIFE SCIENCES Dec 2019) Q. The membrane phospholipid structures in bacteria and archaea differ. Which one of the following correctly states the differences between the two ? (a) The bacterial membrane phospholipid consist of D-glycerol linked to hydrophobic chains (tails) with ester bonds whereas those of the archaeal membranes consist of L-glycerol linked to hydrophobic tails through ether bonds. (b) The bacterial membrane phospholipid consist of L-glycerol linked to hydrophobic chains (tails) with ester bonds whereas those of the archaeal membranes consist of D-glycerol linked to hydrophobic tails through ether bonds. (c) The bacterial membrane phospholipid consist of D-glycerol linked to hydrophobic chains (tails) with ether bonds whereas those of the archaeal membranes consist of L-glycerol linked to hydrophobic tails through ester bonds. (d) The bacterial membrane phospholipid consist of L-glycerol linked to hydrophobic chains (tails) with ether bonds whereas those of the archaeal membranes consists of D-glycerol linked to hydrophobic tails through ester bonds. Explanation Ans: a Bacterial membrane phospholipids have D-glycerol, whereas archaeal membrane phospholipids have L- glycerol. Bacterial membrane phospholipids have ester bonds linking the glycerol to the hydrophobic tails, while archaeal membrane phospholipids have ether bonds. (CSIR NET LIFE SCIENCES June 2016) Q. Which of the following statements is NOT true regarding the closer affinity of Archaea to Eukarya than to Bacteria? (a) Both Archaea and Eukarya lack peptidoglycan in their cell walls. (b) The initiator amino acid for protein synthesis is methionine in both Archaea and Eukarya. (c) Histones associated with DNA are absent in both Archaea and Eukarya. (d) In both Archaea and Eukarya the RNA polymerase is of several kinds. Ans: c Explanation The statement (c) "Histones associated with DNA are absent in both Archaea and Eukarya" is NOT true regarding the closer affinity of Archaea to Eukarya than to Bacteria. This statement is incorrect because histones, which are proteins associated with DNA and involved in its packaging and regulation, are present in Eukarya but absent in Archaea. Therefore, this statement does not support the closer affinity of Archaea to Eukarya.