Bacterial response to environment Rapid response crucial for
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 1
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 2
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 3
Flagellar structures www. scu. edu/SCU/Departments/ BIOL/Flagella. jpg img. sparknotes. com/. . . /monera/ gifs/flagella. gif 4
Runs and Tumbles: bacteria find their way http: //www. bgu. ac. il/~aflaloc/bioca/motil 1. gif 5
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. 6
Axial filaments 7 http: //images. google. com/imgres? imgurl=http: //microvet. arizona. edu/Courses/MIC 420/lecture_notes/spirochetes/gifs/spirochete_crossection. gif& imgrefurl=http: //microvet. arizona. edu/Courses/MIC 420/lecture_notes/spirochete_cr. html&h=302&w=400&sz=49&tbnid=BOVd. Hqe p. F 7 UJ: &tbnh=90&tbnw=119&start=1&prev=/images%3 Fq%3 Daxial%2 Bfilament%2 Bbacteria%26 hl%3 Den%26 lr%3 D%26 sa%3 DG
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_myx ococcus. html 8
Starvation Responses 9 • 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
Extracellular molecules 10 • 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
Sporulation 11 • 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
Endospore formation Genetic cascade producing alternative sigma factors. http: //www. microbe. org/art/endospore_cycle. jpg 12
Responses of microbes to other environmental stresses 13 • 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/ima ges/Betaine. gif
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