Microbiology 2018-1-31 lecture 4 archaeal cell structure PDF

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Microbiology 2018 February 5 LECTURE 4: Archaeal Cell Structure Archaea  

Archaea and bacteria similar in terms of metabolic activity o Cell walls/membranes different from bacteria and eukaryotes Methanogenesis—ability to produce methane as a metabolic byproduct o Unique to Archaea

Size and shape 

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Cocci and rods are common cell shapes o Others include square, vibrio, etc. o No spirillum or spirochetes Sizes vary from 0.1 to >15 μ m

Archaeal cell envelope     

Lack peptidoglycan: instead, some have pseudomurein o Cousin of peptidoglycan Some have S layers as part of cell wall instead of surrounding Some lack cell wall altogether Capsules and slime layers are rare Unique membrane lipids

Archaeal plasma membranes 

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Composed of unique lipids o Lipids have branched hydrocarbon tails o Ether linkages rather than ester linkages to glycerol  Suggested that stronger ether link contributes to capability of Archaea to withstand harsh environments o Glycerol is mirror image from bacteria in terms of stereochemistry Some form monolayers

Archaeal cell walls  

Most common cell wall is an S layer 6 basic types: o S layer, plasma membrane, cytoplasm o Protein sheath, S layer, plasma membrane, cytoplasm o Methanochondroitin, S layer, plasma membrane, cytoplasm o S layer, pseudomurein, plasma membrane, cytoplasm o Polysaccharides, plasma membrane, cytoplasm o Outerost membrane, intermembrane compartment, plasma membrane, cytoplasm

Archaeal cytoplasm   

Nucleoid, not nucleus or nucleolus Inclusion bodies function in stockpiling nutrients Cytoskeletal proteins found in cytoplasm o FtsZ—forms central septum and allows cells to divide

Microbiology 2018 February 5 o MreB—coil shape in center of rod shapes that aids in cell division Nucleoid   

Irregularly shaped region where single chromosome resides Not membrane bound Nucleoid proteins (NAPs) aid in supercoiling of DNA and allowing it to pack into cell

Archaeal external structures   

Pili—assumed to function in attachment to tissues or other environmental surfaces Cannulae—hollow tube-like structures often found on thermophilic (heat-loving) Archaea o Believed to anchor cells to each other and function as means of communication Hami—look like pilli and radiate from outside of cell o Ends look like grappling hooks o Believed to function in attachment and biofilm formation

Differences of Archaeal flagella   

Archaeal flagella are thinner, not hollow, and have multiple types of flagellin protein Hook made up of flagellin subunits Basal body exists

Archaeal DNA replication  

Eukarya-like helicases and DNA polymerases o Helicase—breaks hydrogen bonds to “unzip” DNA during replication Bacteria-like circular chromosomes, plasmids, and bidirectional characteristics o Bidirectional—2 replication forks that occur in both directions

Archaeal transcription 

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TATA box—RNA polymerase recognizes TATA box to start transcription o Called a “pribnow” in bacteria  Shorter consensus sequence Transcription occurs in cytoplasm in Archaea and bacteria and in nucleus in eukaryotes o Most things occur in cytoplasm due to lack of membrane-bound organelles

Archaeal translation   

Bacteria have 70s ribosomes, Archaea have 80s ribosomes o Can undergo coupled transcription and translation Eukaryote-like elongation factors o Many RNA transcripts lack leader sequence st 21 and 22nd amino acids originally discovered in Archaea o Selenocysteine (Sec)—inserted in response to UGA codon in specific instances  Present in some enzymes that protect against oxidative damage o Pyrrolysine (Pyl)—inserted in response to UAG codon in specific instances  Only found in bacteria and Archaea  Thought to play role in methanogenic ability

Protein secretion

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All domains can use Sec system o Archaea can use Sec and Tat systems  Translocation system to move things from inside cell past plasma membrane  Secretion means inside cell to outside cell completely  Sec—unfolded proteins  Tat—folded proteins Diseases mainly caused by secretion of toxins 1/3 of all proteins made within bacterial and Archaeal cells are secreted

Archaeal metabolism 

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3 pathways unique to Archaea o Embden-Meyerhof pathway—modified glycolytic pathway  1 glucose to 2 pyruvates o Entner-Doudoroff pathway—1 glucose to 2 pyruvates Lack pyruvate-dehydrogenase complex o Transition step to form acetyl-coA o Pyruvate oxidoreductase Some lack TCA cycle Use of Calvin cycle and alternative carbon fixation pathways

Thermostability     

Many capable of withstanding high temperatures o Possibly due to stability of proteins Chaperones—partially refold denatured proteins Reverse DNA gyrase—induces positive supercoils in DNA o Tightens and prevents DNA from denaturing Topoisomerase—assists in unwinding of DNA Geogemma barossii (strain 121)—can replicate up to 121oC and replicate up to 130oC o Can survive sterilization in autoclave

Archaeal taxonomy 

Two main phyla: Euryarchaeota, Crenarchaeota o Euryarchaeota  Methanogens—derive energy from converting CO2 and other compounds to methane  Largest group of Archaea  Rods, cocci, curved rods, irregular  Unusual metabolism  Halobacteria—aerobic  Require high salinity for growth o At least 1.5 M NaCl, optimum growth near 3-4 M NaCl  Cubes, pyramids, rods, cocci  Red to yellow pigments  Thermoplasms—thermoacidophiles that lack cell walls  Thermoplasma—59oC, 1-2 pH  Picrophilus—47-65oC, 0 pH  Extreme thermophiles—motile by multiple flagella

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 88-100oC—hydrothermal vents, etc.  Strictly anaerobic  Sulfate-reducers—reduce sulfate to sulfide  Irregular cocci cells  Anaerobes  Optimum 83oC o Crenarchaeota  Sulfolobus—irregularly lobed, aerobic  Thermoacidophiles—70-80oC  pH of 2-3  ABC transporters—proteins embedded in plasma membrane that allow nutrients to make their way into the cell o Used for uptake of sugars into cell  Membranes arranged in monolayers  Thermoproteus—long, thin rods, anaerobic  Thermoacidophiles o 75-100oC, pH of 3-4  Reductive TCA cycle—reverse of Krebs cycle o Carbon fixation pathway resulting in acetyl coA  Membranes arranged in monolayers  Lipotrachus flagella—three on one side Almost all Crenarchaeota are thermoacidophiles o Prefer high temperatures and low pH o

Archaeal cell surfaces  

Euryarchaeota—if S layer is present, it is anchored to plasma membrane o 10-15 nm distance Crenarchaeota—S-layer distance is wider

Compare and contrast All Three Domains    

Have a plasma membrane Have ribosomes DNA, at least one chromosome, some sort of genetic material Have a cytoplasm/cytoplasmic properties

Eukarya  

Nucleus Organelles—mitochondria, ER, Golgi bodies, etc.

Archaea   

Microbial nutrition

Pseudomurein Membrane lipids have ester linkages Stereochemistry of glycerol

Bacteria   

Peptidoglycan Sporylation Hopanoids

Microbiology 2018 February 5   

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Nutrients used for variety of metabolic functions Passive diffusion—high to low concentration o H2O, O2, CO2 Facilitated diffusion—non-energy-dependent diffusion using transport proteins o Channels— o Carriers— o Smaller concentration gradient required o Larger molecules can be passed through membrane  Sugars, amino acids, etc. o Solute binding causes conformational change o Solutes will move based on gradient Active transport—low concentration to high concentration o Energy-dependent (ATP) o Uses transport proteins o Primary active transport—uses ATP  Molecule is not modified o Secondary active transport—use potential energy of ion gradients to transport substances  Symport (coupled transport)—movement of two substances in the same direction  Common for sodium, glucose  Antiport—movement of two substances in opposite directions  Common for sodium, calcium o Group translocation—low concentration to high concentration  Energy dependent  Glucose  PEP  Enzyme I  HPr  Enzyme IIA  Enzyme IIB—phosphorylates glucose  Enzyme IIC  Chemically modifies molecules  Phosphenolpyruvate-sugar phosphotransferase system (PTS)—phospho-relay system

Iron uptake   

Required by microorganisms Difficult to take into cell and not always abundant in environment Siderophores—molecules that bind iron o Can be secreted from cell and taken back into cell through ABC transporter o Ferrichrome—fungal siderophore o Enterobactin—bacterial siderophore

Culture media   

Solid or liquid medium used to grow, transport, and store microbes Must contain all the nutrients required by the organism for growth Examples: nutrient agar (solid), nutrient broth (liquid)

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Functional types of media  

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Supportive—supports many microorganisms o I.e. tryptic soy agar Enriched—good for fastidious microorganisms o Specific nutritional requirements o I.e. blood agar—often used for bacteria that grows in humans Selective

Differential media 

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Distinguishes microbes by their biological characteristics o I.e. blood agar—hemolytic vs nonhemolytic bacteria o I.e. MacConkey agar—lactose fermenters versus nonfermenters Different microbes appear different

Isolation of pure cultures    

Colony—population of cells arising from a single cell Single colony moved to a separate vessel and grown on its own HAVE NOT COMPLETED CREATING A NEW COLONY UNTIL IT IS MOVED TO A FRESH VESSEL Methods of colony isolation: o Spread plate—small volume of diluted mixture spread evenly over surface with a sterile bent rod o Streak plate—streak mixed culture on plate  Each cell can reproduce to form a separate colony  Use a single colony to create a pure culture  Split Petri dish into four quadrants, drag bacteria from first quadrant to second quadrant with sterile inoculation loop, repeat for rest of quadrants o Pour plate—mixture of cells and agar are poured into sterile culture dishes  Sample is serially diluted  Mixed with hot liquid agar and poured onto Petri dish...