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

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 to– 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

img.sparknotes.com/.../monera/ gifs/flagella.gif

www.scu.edu/SCU/Departments/ BIOL/Flagella.jpg

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?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=BOVdHqepF7UJ:&tbnh=90&tbnw=119&start=1&prev=/images%3Fq%3Daxial%2Bfilament%2Bbacteria%26hl%3Den%26lr%3D%26sa%3DG

8

Gliding Motility

Movement on a solid surface.Cells produce, move in slime trails.Cells glide in groups, singly, andcan 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

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 surface:volume)– Induction of low Km uptake systems– Release of extracellular enzymes, scavenging molecules– Production of resting cells, spores

10

Smaller size is better 11

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.

Different Transport proteins 12

Bacteria switch to transport systems that work better at lower solute concentration.

13Extracellular 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

Siderophores

14

http://www-users.york.ac.uk/~srms500/research_group/pic_1.JPG

http://www.staff.uni-marburg.de/~oberthue/enterobactin.gif

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 can’t protect itself well

15

16Endospore formation

http://www.microbe.org/art/endospore_cycle.jpg

Genetic cascade producing alternative sigma factors.

17Responses 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/mikrobio/

molmibi/forschung/osmostress-response/image_preview

Compatible solutes

• small neutral molecules accumulated in cytoplasm when external environment is hypertonic.

• No net charge, not acidic or basic.

18

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.

19

http://www.tulane.edu/~biochem/med/shock.gif