Global control: modulons

1
Global control modulons

• Different operons/regulons affected by same
  environmental signal
• 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

2
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
• Change from aerobic to anaerobic
• Presence/absence of glucose
• Amount of nutrients in general
• Presence of specific nutrients
• Population size

3
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

4
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

5
Flagellar structures
www.scu.edu/SCU/Departments/ BIOL/Flagella.jpg
img.sparknotes.com/.../monera/ gifs/flagella.gif
6
Runs and Tumbles bacteria find their way
http//www.bgu.ac.il/aflaloc/bioca/motil1.gif
7
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.

8
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
sz49tbnidBOVdHqepF7UJtbnh90tbnw119start1
prev/images3Fq3Daxial2Bfilament2Bbacteria26
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9
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
10
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)
• Induction of low Km uptake systems
• Release of extracellular enzymes, scavenging
  molecules
• Production of resting cells, spores

11
Smaller size is better
Increased surface to volume ratio Surf 4 p r2
Vol 4/3 p 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
cells interior. Smaller cell more easily
maintained.
12
Different Transport proteins
Bacteria switch to transport systems that work
better at lower solute concentration.
13
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

14
Siderophores
http//www.staff.uni-marburg.de/oberthue/enteroba
ctin.gif
http//www-users.york.ac.uk/srms500/research_grou
p/pic_1.JPG
15
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

16
Endospore formation
Genetic cascade producing alternative sigma
factors.
http//www.microbe.org/art/endospore_cycle.jpg
17
Responses of microbes to hypertonicity

• 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.uni-marburg.de/fb17/fachgebiete/mikrobi
o/molmibi/forschung/osmostress-response/image_prev
iew
18
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
19
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