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Determination of Bacterial Chemotaxis Response Functions by Optical Trapping

Altindal, Tuba (2012) Determination of Bacterial Chemotaxis Response Functions by Optical Trapping. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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A two-lobe response function is considered as a manifestation of temporal signal comparison in bacterial chemosensing. The second lobe in the response function appears as a result of adaptive behavior of the underlying signaling network, which allows bacteria to stay sensitive over a wide range of background signal levels. It has been argued that this two-lobe response reflects the dual requirements of the bacteria to taxis along a chemical gradient and to localize once the top of the gradient is reached. Calculations based on the run-tumble motility pattern of Escherichia coli showed that the second lobe improved the bacterium's localization capability. Intrigued by a recently observed run-reverse-flick motility cycle of a marine bacterium Vibrio alginolyticus, we investigate the motility-response relationship in this bacterium. Using a novel optical trapping technique, we measure the response of V. alginolyticus to an impulsive stimulus of chemoattractant serine. By exploiting an asymmetry in the rotation of the polar flagellum, we are able to determine for the first time how the bacterium responds to chemical stimuli while swimming forward or backward. Our measurements suggest that this marine bacterium regulates its forward and backward swimming intervals differently, exhibiting behaviors that is consistent with an exploration-exploitation strategy.
In our measurements, we also find that the cell-body Ω(t) and the flagellar ω(t) rotational angular frequencies oscillate in time and are in synchrony with the forward and backward swimming intervals. Unexpectedly, Ω(t) and ω(t) are found to be anticorrelated in that the cell body rotates slower in the forward direction than in the backward direction, Ωf<Ωb, but the flagellum rotates faster in the forward direction than in the backward direction. The change in the rotational load (~25%) is significantly greater than that predicted by flagellum deformation but can be accounted for by the precession of the flagellum about the body axis during the backward swimming interval. We postulate that as a result of the precession, a kink is generated at the base of the flagellum that is subsequently amplified when the flagellum motor reverses direction, leading to the flick, the direction randomization step in V. alginolyticus' motility pattern.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Altindal, Tubatua7@pitt.eduTUA7
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairWu, Xiao-Lun
Committee MemberGoldburg, Walter I
Committee MemberSalman, Hanna
Committee MemberSwanson, Eric S
Committee MemberDuda, Robert L
Date: 11 June 2012
Date Type: Publication
Defense Date: 23 January 2012
Approval Date: 11 June 2012
Submission Date: 19 April 2012
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 158
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Physics
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Bacterial chemotaxis, Vibrio alginolyticus, optical tweezers, chemotactic response function
Date Deposited: 11 Jun 2012 16:20
Last Modified: 15 Nov 2016 13:57


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