Relationship between cellular response and behavioral variability in bacterial chemotaxis
Original Entry: Tom Dimiduk APPHY, Fall 2010
Relationship between cellular response and behavioral variability in bacterial chemotaxis Thierry Emonet† and Philippe Cluzel Proceedings of the National Academy of Sciences
Soft Matter Keywords
Random Walk, Fluctuation Dissipation, Population Behavior
This article discusses how amplification of noise in an enzyme regulation system is used to drive the bacteria's stochastic response to nutrient gradients. The authors find that hypersensitivity to these fluctuations actually provides beneficial behaviors both for allowing single bacteria to progress rapidly up gradients and for allowing populations to explore a large area. Finally, the dynamics of bacteria in response to stimulus can be inferred from their spontaneous fluctuations in the absence of stimuli.
Soft Matter Discussion
This paper presents only computational results, though they point at a previous paper with supporting experimental work. Any reference to cells or mutants here actually refers to simulated cells and simulated cells expressing a simulated mutant phenotype.
The first portion of their results is a lengthy discussion of enzyme dynamics which is of little interest from a soft matter perspective. The important results from this section are that increasing expression of the CheY-P kinase (1) reduces fluctuations in control loops (Figure 3), reducing the power spectrum of the cell's motion, and (2) decreases the relaxation time in response to stimulus.
They observe that the decrease in relaxation time caused by increasing expression of CheY-P shortens the length of runs while going up a gradient (Figure 4a,b), reducing the rate at which the bacteria travel up a gradient (Figure 4c).
The large fluctuations in wild type bacteria cause more spread along directions perpendicular to the gradient than mutants with damped noise, as shown in Figure 4d. This spread is broadened by increased variability in behavior between bacteria within the population. They state that this is beneficial for a population because it allows a colony as a whole to explore larger spaces in the search for nutrients.