Archaeal Cell Structure. Copyright McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display.

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1 4 Archaeal Cell Structure Copyright McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display. 1

2 4.1 A typical Archaeal Cell 2

3 Archaea Highly diverse with respect to morphology, physiology, reproduction, and ecology Best known for growth in anaerobic, hypersaline, ph extremes, and high-temperature habitats Also found in marine arctic temperature and tropical waters Genes encoding proteins for replication, transcription, translation are common with Eukarya, whereas genes for metabolism are common with Bacteria Archaea has unique rrna gene structure and is capable of methanogenesis 3

4 Archaeal size, shape, arrangement Much like bacteria, cocci and rods are common shapes Other shapes can also exist Sizes vary (typically 1-2 x 1-5 μm for rods, 1-5 μm in diameter for cocci) Smallest observed is 0.2 μm in diameter Largest is a multicellular form that can reach 30 mm in length! 4

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6 Bacteria vs. Archaeal in cell structure 6

7 4.2 Archaeal Cell Envelopes 1. Cell wall 2. Cell membrane 3. The uptake system on the membrane 7

8 Archaeal cell wall structure Some lack cell wall Lack peptidoglycan; Most common cell wall is S layer; may have protein sheath external to S layer S layer may be outside membrane and separated by pseudomurein Pseudomurein may be outermost layer similar to Gram-positive microorganisms only Ignicoccus has outer membrane 8

9 Peptidoglycan vs. Pseudomurein Peptidoglycan: Glycan backbone: N-acetylmuramic acid (NAM) and N- acetylglucosamine (NAG), linked by β-1 4 bond. Peptide bridge: 4 alternating D- and L-amino acids attaching to NAM Pseudomurein: Glycan backbone: N-acetylalosminuronic and N- acetylglucosamine (NAG), linked by β-1 3 bond. Peptide bridge: L-amino acids attaching to N- acetylalosminuronic Questions: 1. Can archaea be stained with Gram staining? 2. Can penicillin inhibit Archaea growth? 9

10 ex. Ignicoccus 10

11 Archaeal Membranes Composed of unique lipids isoprene units (five carbon, branched) ether linkages rather than ester linkages to glycerol Some have a monolayer structure instead of a bilayer structure 11

12 Archaeal Membrane Lipids Differ from Bacteria and Eukarya in having branched chain hydrocarbons attached to glycerol by ether linkages Polar phospholipids, sulfolipids, glycolipids, and unique lipids are also found in archaeal membranes 12

13 branched chain hydrocarbons attached to glycerol by ether linkages some have diglycerol tetraethers Fatty acids attached to glycerol by ester linkages 13

14 Archaeal cells and nutrient uptake Archaeal cells use many of the same mechanisms for nutrient uptake exhibited in bacteria facilitated diffusion active transport (primary and secondary) No group translocation mechanisms have yet been discovered in archaea, however 14

15 4.3 Archaeal cytoplasm Ribosome, nucleoid, inclusion body and others 15

16 Archaeal vs. bacterial cytoplasm Very similar; both lack of membrane-enclosed organelles May contain inclusion bodies (e.g. gas vesicles for buoyancy control) All the usual components Ribosomes: in addition to 16S, 23S and 5S, archaea have additional 5.8S (also seen in eukaryotic large subunit) nucleoid region inclusion bodies Some structures may be different, however Archaeal proteins are more similar to eukarya than to bacteria 16

17 4.4 External structures 1. Pili 2. Cannulae 3. Hami 4. Flagella 17

18 Archaeal external structures: Pili not well understood as of yet some composed of pilin protein and homologous to bacterial type IV pili proteins pili formed have a central lumen similar to bacterial flagella, but not bacterial pili may be involved in archaeal adhesion mechanisms 18

19 Archaeal external structures: Cannulae hollow, tubelike structures on the surface of thermophilic archae in the genus Pyrodictium function is unknown may be involved in formation of networks of multiple daughter cells 19

20 Archaeal external structures: Hami not well understood grappling hook appearance involvement in cell adhesion mechanisms? 20

21 Archaeal external structures: Flagella Flagella thinner than that in bacteria More than one type of flagellin protein Flagellum are not hollow Hook and basal body difficult to distinguish More related to Type IV secretions systems Growth occurs at the base, not the end 21

22 Comparison of Bacteria and Archaea 5.8S 22

23 5/16 Homework 1. Compare and contrast archaeal and bacterial cell envelopes in terms of structure, molecular makeup and functions. 2. Compare and contrast nutrient uptake mechanisms observed in bacteria and archaea. 3. Describe cannulae and hami. What are the observations to suggest that they participate in adherence? 4. Archaea are often described as hybrid organisms (of bacteria and eukaryotes). Explain. 23