Chapter 2 Microbial Cell Structure and Function Chapter 2. Microbial Cell Structure and Function (self study) 2.6 2.7 2.8 2.9 2.10 2.11 2.12 Cell Surface Structures Cell Inclusions Endospores Flagella, Archaella, and Swimming Motility Surface Motility Chemotaxis Other forms of Taxis 2.13-2.15 skip this 2.6 Cell Surface Structures Leuconostoc Acinetobacter Capsules and slime layers - Polysaccharide layers (thich, thin, rigid or flexible) - capsule: if tightly attached, tight matrix; - slime layer: loosely attached, easily deformed Function - Formation dependent on environmental conditions (C/N ratio; [O2]) - assist in attachment to surfaces - role in development of biofilms - protect against phagocytosis - prevent dehydration/desiccation cell capsules Rhizobium trifolii 2.6 Cell Surface Structures Prevent dehydration/desiccation Haloquadra walsbyi , Extreme halophilic archaeon. Has a special slime layer called halomucin (a protein!!!). Large protein of 9159 amino acids. Binds water molecules,due to negatively charged amino groups. Red = PHB Green = halomucin 2.6 Cell Surface Structures Role in development and maintenance of biofilms Steps in biofilm formation on a solid surface Van der Waals → Electrostatic → fimbriae → exopolymers Yellowstone NP 2.6 Cell Surface Structures Fimbriae: - filamentous protein structures - 2-10 nm wide - ~1000/cell - enable organisms to stick to surfaces Pili: - filamentous protein structures - 9-10 nm wide - ~1-10/cell - genetic exchange between cells (conjugation) - transport of electrons (Flagella will be discussed later) 2.6 Cell Surface Structures Certain archaea have a special type of pilus, called hamus (plural, hami) Used for attachment to surfaces and each other (making biofilms) Intermezzo: electron transfer via pili Transport of electrons: Most energy-generating (ATP) systems in microorganisms involve redox reactions: “transport of electrons from a donor to an acceptor” E. coli Electron donor (energy source): Electron acceptor (respiration): Carbon source: glucose ½O2 + 2e- → H2O glucose Shewanella lactate Fe3+ + e- → Fe2+ lactate other nutriënts: N, P, S, Mg, Fe, ... We have seen already that oxygen can be used as e-acceptor. But Shewanella breathes with oxidized iron (Fe3+). Intermezzo: electron transfer via pili Shewanella oxidizes lactate (C3H6O3) and uses Fe3+ as elektron acceptor (for respiration), yielding Fe 2+. Fe3+ is insoluble and precipitates on the pili (Fe2O3). Shewanella is able to dispose of electrons on the outside of the cell, makinguse of the pili. Can we make use of this feature? Shewanella Intermezzo: electron transfer via pili Electricity from organic waste using a microbial fuel cell https://www.youtube.com/watch?v=lj23qMhpVcg Shewanella can donate its electrons to the anode and the electrons are transferred to oxygen at the cathode. So there will be a current We call this a microbial fuel cell. Lactate Shewanella Microbial fuel cell 2.7 Cell Inclusions Inclusions function as - energy reserves - carbon reservoirs - and/or have special functions. - enclosed by thin membrane - reduce osmotic stress monomer can vary in length from C3 to C18 → generic term: polyhydroxyalkanoate (PHA) Carbon/energy storage - poly-β-hydroxybutyric acid (PHB) - glycogen: glucose polymer Rhodovibrio sodomensis 2.7 Cell Inclusions Polyphosphate granules: inorganic phosphate (HPO3)n Acinetobacter (n >500) Sulfur globules: elemental sulfur found in periplasm Thiomargarita namibiensis Magnetosomes: magnetic iron oxides; allow cell to orient using the magnetic field of the earth (magnetotaxis). Magnetospirillum magnetotacticum Magnetotactic bacteria all motile (flagella) respond to O2-concentration mostly micro-aerophilic (1-2% O2 = 0.1-0.2 mg/l) Magnetiet: Fe2+Fe3+2O4 or greigite Fe2+Fe3+2S4 causes magnetic dipole → orient in magnetic field (~compass needle) membrane 2.7 Cell Inclusions - Gas Vesicles 2.7 Cell Inclusions - Gas Vesicles Microbiologial misconceptions: 1. ‘blue-green algae’ are not always blue-green 2. ‘blue-green algae’ are not algae, but bacteria (cyanobacteria) 3. ‘blue-green algae’ are not always harmful 4. bacteria do differentiate Gas vesicles are often observed among cyanobacteria 2.7 Cell Inclusions - Gas Vesicles • Confer buoyancy in planktonic cells • Take up gas from the surrounding water phase • Depending on the light intensity they enable rising or descending • Conical-shaped, gas-filled structures made of protein • Impermeable to water and solutes • Gas vesicle are composed of two proteins, GvpA and GvpC. gas vesicle bundle of gas vesicles 2.7 Cell Inclusions - Gas Vesicles Haloquadra walsbyi : GV: gasvesicle Gas vesicles help to orient the cells near the surface and parallel to the surface. ) 2.8 Endospores Endospores: - Survival structures to endure unfavorable growth conditions (dormant stage) - Present only in some gram-positive bacteria (e.g., Bacillus and Clostridium) - Highly differentiated cells resistant to heat, harsh chemicals, and radiation De location of the spore in the cell may differ 2.8 Endospores vegetative cell unfavorable conditions Three steps: activation, germination, and outgrowth germination activation: heated for several minutes at elevated but sublethal temperature germination: rapid loss of refractility and loss of resistance to heat and chemicals outgrowth: swelling from water uptake and synthesis of RNA, proteins, and DNA 2.8 Endospores Structure and features • many layers: exosporium, spore coat, cortex, core • contains dipicolinic acid • enriched in Ca2+ Dipicolinic acid: • found in all spores • complex with Ca2+ • ~10% of dry weight • binds water and stabilizes DNA Cell undergoing sporulation 2.8 Endospores How long can spores survive? Some reports say 28 – 250 million years. Solid proof is missing. Bacteria isolated from abdomen of ancient bee and revived by microbiologist Raul Cano of California Polytechnic State University, USA, 1995 The age of the bacteria was determined from microscopic fossils in the rock strata from which the amber comes (~28 million years) From a 250 million-year-old salt crystal an unknown Bacillus species was isolated (Vreeland et al. 2000) 2.9 Flagella, Archaella, and Swimming Motility Flagellar and flagellation • long, thin appendages (15–20 nm wide); helical shape; composed of flagellin • different arrangements: polar, lophotrichous, amphitrichous, peritrichous • tiny rotating machines (reversible) • increase or decrease rotational speed relative to strength of proton motive force 14 nm 2.9 Flagella, Archaella, and Swimming Motility L filament P flagellin MS proton-motive-force drives the rotation of the flagellum hook outer membrane (LPS) L ring rotor staaf P ring periplasm peptidoglycan MS ring C ring cytoplasmic membrane Mot protein (H+-ions) Fli proteins (motor switch) 45 nm Mot protein Fli proteins reverse the direction of rotation in response to intracellular signals (BTW you do not need to know all flagellum parts) 2.11 Flagella, Archaella, and Swimming Motility Flagellar synthesis: - more than 50 genes - filament grows from tip - build from cytoplasmic membrane - flagelline produced in cytoplasm 2.9 Flagella, Archaella, and Swimming Motility How fast can it rotate? E. coli ~ 18,000 rotations/min ~ 60 cel lengths/sec (0,17 m/hour) V. cholerae ~ 66,000 rpm NB niet aangedreven door PMF maar Sodium Motive Force (Na-gradient) http://www.arn.org/docs/mm/flagellum_all.htm 2.9 Flagella, Archaella, and Swimming Motility Archaella • half the diameter of bacterial flagella (10–13 nm) • move by rotation • composed of several different filament proteins with little homology to bacterial flagellin • speeds vary from 0.1–10x Escherichia coli • structurally similar to type IV pili • driven by ATP (not the PMF) archaella (Methanococcus maripaludis ) 2.10 Surface Motility - bacteria only requires surface contact slower and smoother than swimming different mechanisms • excretion of polysaccharide slime • type IV pili/twitching motility • gliding-specific proteins Flavobacterium johnsoniae gliding away from colony non-gliding mutant Oscillatoria princeps Oscillatoria princeps 2.11 Chemotaxis Taxis: directed movement in response to chemical or physical gradients • chemotaxis: response to chemicals • phototaxis: response to light • aerotaxis: response to oxygen • osmotaxis: response to ionic strength • hydrotaxis: response to water chemotaxis best studied in E.coli (peritrichous) runs are longer, less tumbling 2.11 Chemotaxis and Other Taxes - Differences in direction of rotation (clock wise /counter cock wise) - Many differences seen between different bacteria and the position of the flagel(la) 2.11 Chemotaxis receptor (MCP) How to sense a gradient? → Specific receptor proteins (MCP). The signal is transmitted to the flagellum. How that happens, you do not need to know. cytoplasmic membrane antibodies against receptor proteins 2.11 Chemotaxis Measuring chemotaxis • measured by inserting a capillary tube containing an attractant or a repellent in a medium of motile bacteria • can also be seen under a microscope 2.12 Other forms of Taxis Phototaxis green algae Chlamydomonas “randomly oriented tracks formed during 1/3 sec by the algae swimming about in red light to which they are insensitive”. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Taxes.html “upon adding a beam of blue-green light from one side, the tracks become oriented in its direction”.
