Transcript Bacterial response to environment

Global control: modulons
• Different operons/regulons affected by same
environmental signal
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Presence of glucose
Change from O2 to anaerobic growth
Nitrogen limitation; phosphate starvation
Oxidative stress
Stationary phase; entering starvation state
• Some methods of control:
– alternate sigma factors; Sigma controls which promoters
are used
– cAMP and CRP
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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 to
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Change from aerobic to anaerobic
Presence/absence of glucose
Amount of nutrients in general
Presence of specific nutrients
Population size
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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
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Chemotaxis and other taxes
• Movement in response to environmental stimulus
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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
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Flagellar structures
www.scu.edu/SCU/Departments/ BIOL/Flagella.jpg
img.sparknotes.com/.../monera/ gifs/flagella.gif
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Runs and Tumbles: bacteria find their way
http://www.bgu.ac.il/~aflaloc/bioca/motil1.gif
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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.
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Axial filaments
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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=BOVdHqe
pF7UJ:&tbnh=90&tbnw=119&start=1&prev=/images%3Fq%3Daxial%2Bfilament%2Bbacteria%26hl%3Den%26lr%3D%26sa%3DG
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
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Starvation Responses
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• 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
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Lower metabolic rates, smaller size (incr surface:volume)
Induction of low Km uptake systems
Release of extracellular enzymes, scavenging molecules
Production of resting cells, spores
Smaller size is better
Increased surface
to volume ratio
Surf = 4 π r2
Vol = 4/3 π r3
Nutrients enter through cell surface; the more surface,
the more nutrients can enter.
Large interior means slow diffusion, long distances.
The larger a sphere, the LOWER the surface/volume,
creating “supply” problems to the cell’s interior.
Smaller cell more easily maintained.
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Uptake Rate
Different Transport proteins
Kinetics of
Uptake systems
low Km
High Km system
Low Km system
high Km
0.000
0.100
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0.400
0.500
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[solute]
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0.900
1.000
Bacteria switch
to transport
systems that
work better at
lower solute
concentration.
Extracellular molecules
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• 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
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Siderophores
http://www.staff.uni-marburg.de/~oberthue/enterobactin.gif
http://www-users.york.ac.uk/~srms500/research_group/pic_1.JPG
Sporulation
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• 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
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Responses of microbes to hypertonicity
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• If cell is in a
hypertonic
environment,
water leaves
the cell.
Decrease of intracellular water causes proteins, etc. to
precipitate out of solution, stop functioning.
Bacteria respond by increasing the concentration of
“compatible solutes” to partially balance the higher
external solute concentration. http://www.unimarburg.de/fb17/fachgebiete/mikrobio/molmibi/forschung/
osmostress-response/image_preview
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Compatible solutes
• small neutral molecules accumulated in
cytoplasm when external environment is
hypertonic.
• No net charge, not acidic or basic.
http://www.thermera.com
/images/Betaine.gif
Stress proteins
• Elevated temperatures turn on Heat shock proteins
– Proteins help protect and repair other critical
proteins in the cell
– Heat and other
environmental stresses
turn on genes for these
protective proteins.
http://www.tulane.edu/~biochem/med/shock.gif
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