Bacterial response to environment

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?imgurlhttp//micr
ovet.arizona.edu/Courses/MIC420/lecture_notes/spir
ochetes/gifs/spirochete_crossection.gifimgrefurl
http//microvet.arizona.edu/Courses/MIC420/lecture
_notes/spirochetes/spirochete_cr.htmlh302w400
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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_my
xo/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
  surfacevolume)
• Release of extracellular enzymes, scavenging
  molecules
• Production of resting cells, spores
• Induction of low Km uptake systems

10
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

11
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 cant protect itself well

12
Endospore formation
Genetic cascade producing alternative sigma
factors.
http//www.microbe.org/art/endospore_cycle.jpg
13
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