GMU:Synthetic Biology/Bacteria Game/HowTo: Difference between revisions

Prepare the '''agar''' with '''nutrient powder''' and fill it up with water, following the enclosed protocols. '''Boil''' the media in your microwave until the mixture turns clear and the seems to be completely dissolved. Let it cool down to approx. 50°C. Plates for the challenge have to be '''poured''' with 35 ml. The mixture can be supplied with antibiotics and inducers. Feel free to establish your own procedures. It turned out to be most precisely to inoculate by carefully pipetting 3 μl of '''liquid culture''' into the '''solidified''' agar. Nevertheless, swarm plates can also be inoculated by transferring a bacteria colony using a tooth-pick which can found in the game kit. Swarm plates are ordinarily '''incubated''' at room temperature.

[[File:Figure swarm.jpg | thumb | 400px | figure: swarming bacteria (Adlung, 2010)]]

''E. coli'' cells with a functional chemotactic system swarm (= “swim”) on soft agar plates.

The field of '''chemotaxis''' is perspicuously defined. Studies deal with migration depending on chemicals. To be more precise: cells '''sense''' the presence of diverse substances in their environment and respond to gradients of chemical attractants or repellents by moving. The bacteria spread radially due to the attractant gradients formed by '''metabolizing''' the different nutrients in the agar.  

'''Swimming''' of the cells can be described as a '''biased random walk''' in a '''spatial gradient''' of media. The microbe runs in favorable directions towards high concentrations of '''attractant''' (i. e. nutrient) and away from '''repellents''' (i. e. antibiotic). Straight '''runs''' are only interrupted by '''short tumbles''' where the cell reorients randomly for the next run. The probability for tumbling increases with higher repellent concentrations. Likewise the tumbling frequency rises during runs down attractant gradients (see figure on the right). As a result, the cell almost swims along curly '''trajectories'''.