Interdependence of behavioural variability and response to small stimuli in bacteria
Original Entry: Peter Foster, AP 225, Fall 2011
Authors: Heungwon Park, William Pontius, Calin C. Guet, John F. Marko, Thierry Emonet & Philippe Cluzel
Publication: Park et al. Interdependence of behavioural variability and response to small stimuli in bacteria. Nature (2010) vol. 468 (7325) pp. 819-U114
The goal of this paper  was to test whether or not a connection could be made between between natural variability and stimulus response in cells. This was examined using the E. coli chemotaxis network. The chemotaxis network regulates cellular movement by controlling whether flagella rotate in the clockwise (CW) or counterclockwise (CCW) direction. When the flagella rotate in the CCW direction, they form a bundle and propel the cell forward and when they rotate in the CW direction the bundle unravels and randomly orients the cell. The signaling network serves to regulate the probability that the motors rotate in the CW vs. the CCW direction. Because of the stochastic nature of signaling events, there is a variability of CW bias between different cells in the steady state. Furthermore, for a given input stimulus, the response time varies between cells. In this paper the connection is drawn between this variability and response.
Figure 1(a) shows the natural variance of the CW bias between cells in the steady state.
- FRT extension of FDT to system far from thermal equilibrium To me, what's really interesting about this paper is that it shows how it's possible to extend something like the fluctuation-dissipation theorem. The fluctuation-dissipation theorem is only valid for fluctuations of systems that are at thermal equilibrium. However, many interesting systems (including living biological systems) exist far from thermal equilibrium. This paper shows that the fluctuation response theorem (an extension of the fluctuation dissipation theorem) can be valid for some biological systems.
 Park et al. Interdependence of behavioural variability and response to small stimuli in bacteria. Nature (2010) vol. 468 (7325) pp. 819-U114