Transcript 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
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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
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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
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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)
Release of extracellular enzymes, scavenging molecules
Production of resting cells, spores
Induction of low Km uptake systems
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
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 other
environmental stresses
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• 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