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Bacterial response to environment

Bacterial response to environment. Rapid response crucial for survival Simultaneous transcription and translation Coordinate regulation in operons and regulons Global genetic control through modulons Bacteria respond Change from aerobic to anaerobic Presence/absence of glucose

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Bacterial response to environment

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  1. Bacterial response to environment • Rapid response crucial for survival • Simultaneous transcription and translation • Coordinate regulation in operons and regulons • Global genetic control through modulons • Bacteria respond • Change from aerobic to anaerobic • Presence/absence of glucose • Amount of nutrients in general • Presence of specific nutrients • Population size

  2. Quorum Sensing • Bacteria monitor their own population size • Pathogenesis: do not produce important molecules too soon to tip off the immune system. • Light production: a few bacteria make feeble glow, but ATP cost per cell remains high. • Bacteria form spores when in high numbers, avoid competition between each other. • System requirements • A signaling molecule that increases in concentration as the population increases; LMW • A receptor; activation of a set of genes

  3. Chemotaxis and other taxes • Movement in response to environmental stimulus • Positive chemotaxis, attraction towards nutrients • Negative: away from harmful chemicals • Aerotaxis: motility in response to oxygen • Phototaxis: motility to certain wavelengths of light • Magnetotaxis: response to magnetic fields • Taxis is movement • Includes swimming through liquid using flagella • Swarming over surfaces with flagella • Gliding motility, requiring a surface to move over

  4. Flagellar structures www.scu.edu/SCU/Departments/ BIOL/Flagella.jpg img.sparknotes.com/.../monera/ gifs/flagella.gif

  5. Runs and Tumbles: bacteria find their way http://www.bgu.ac.il/~aflaloc/bioca/motil1.gif

  6. Motility summarized • Flagella: protein appendages for swimming through liquid or across wet surfaces. • Axial filament: a bundle of internal flagella • Between cell membrane and outer membrane in spirochetes • Filament rotates, bacterium corkscrews through medium • Gliding • No visible structures, requires solid surface • Slime usually involved.

  7. Axial filaments http://images.google.com/imgres?imgurl=http://microvet.arizona.edu/Courses/MIC420/lecture_notes/spirochetes/gifs/spirochete_crossection.gif&imgrefurl=http://microvet.arizona.edu/Courses/MIC420/lecture_notes/spirochetes/spirochete_cr.html&h=302&w=400&sz=49&tbnid=BOVdHqepF7UJ:&tbnh=90&tbnw=119&start=1&prev=/images%3Fq%3Daxial%2Bfilament%2Bbacteria%26hl%3Den%26lr%3D%26sa%3DG

  8. Gliding Motility Movement on a solid surface. Cells produce, move in slime trails. Cells glide in groups, singly, and can reverse directions. Unrelated organism glide: myxobacteria, flavobacteria, cyanobacteria; Recent data support polysaccharide synthesis, extrusion model. http://cmgm.stanford.edu/devbio/kaiserlab/about_myxo/about_myxococcus.html

  9. Starvation Responses • Bacteria frequently on verge of starvation • Rapid utilization of nutrients by community keeps nutrient supply low • Normal life typical of stationary phase • Bacteria monitor nutritional status and adjust through global genetic mechanisms • Types of responses • Lower metabolic rates, smaller size (incr surface:volume) • Release of extracellular enzymes, scavenging molecules • Production of resting cells, spores • Induction of low Km uptake systems

  10. Type of molecule affects transport • Small molecules can pass through a lipid bilayer • Water; otherwise, no osmosis • Gases such as O2 and CO2 • Lipid molecules can • Dissolve in lipid bilayer, pass through membrane • Many antibiotics, drugs are lipid soluble • Larger, hydrophilic molecules cannot • Ions, sugars, amino acids cannot pass through lipids • Transport proteins required

  11. Extracellular molecules • Enzymes • Polymers cannot enter cells • Proteins, starch, cellulose all valuable nutrients • Enzymes produced and released from the cell • LMW products taken up; nutrients gathered exceed energy costs. • Low molecular weight aids • Siderophores, hemolysins collect iron • Antibiotics may slow the growth of competition when nutrients are in short supply

  12. Sporulation • Resting cells • Cells respond to low nutrients by sporulation or slowing down metabolic rate, decr size. • Some cells change shape, develop thick coat • Endospores form within cells; very resistant. • Spores in bacteria generally are for survival • Not reproduction • A spore structure protects cells against drying, heat, etc. until better nutrient conditions return • An inactive cell can’t protect itself well

  13. Endospore formation Genetic cascade producing alternative sigma factors. http://www.microbe.org/art/endospore_cycle.jpg

  14. Responses of microbes to other environmental stresses • Compatible solutes: small neutral molecules accumulated in cytoplasm when external environment is hypertonic. • Heat shock proteins and other stress proteins • Bacteria express additional genes that code for protective proteins. http://www.thermera.com/images/Betaine.gif

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