Dynamics of mechanosensing in the bacterial flagellar motor
Mechanosensing by flagella is thought to trigger bacterial swarmer-cell differentiation, an important step in pathogenesis. How flagellar motors sense mechanical stimuli is not known. To study this problem, we suddenly increased the viscous drag on motors by a large factor, from very low loads exper...
Saved in:
Published in | Proceedings of the National Academy of Sciences - PNAS Vol. 110; no. 29; pp. 11839 - 11844 |
---|---|
Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
United States
National Academy of Sciences
16.07.2013
National Acad Sciences |
Subjects | |
Online Access | Get full text |
Cover
Loading…
Summary: | Mechanosensing by flagella is thought to trigger bacterial swarmer-cell differentiation, an important step in pathogenesis. How flagellar motors sense mechanical stimuli is not known. To study this problem, we suddenly increased the viscous drag on motors by a large factor, from very low loads experienced by motors driving hooks or hooks with short filament stubs, to high loads, experienced by motors driving tethered cells or 1-μm latex beads. From the initial speed (after the load change), we inferred that motors running at very low loads are driven by one or at most two force-generating units. Following the load change, motors gradually adapted by increasing their speeds in a stepwise manner (over a period of a few minutes). Motors initially spun exclusively counterclockwise, but then increased the fraction of time that they spun clockwise over a time span similar to that observed for adaptation in speed. Single-motor total internal reflection fluorescence imaging of YFP–MotB (part of a stator force-generating unit) confirmed that the response to sudden increments in load occurred by the addition of new force-generating units. We estimate that 6–11 force-generating units drive motors at high loads. Wild-type motors and motors locked in the clockwise or counterclockwise state behaved in a similar manner, as did motors in cells deleted for the motor protein gene fliL or for genes in the chemotaxis signaling pathway. Thus, it appears that stators themselves act as dynamic mechanosensors. They change their structure in response to changes in external load. How such changes might impact cellular functions other than motility remains an interesting question. |
---|---|
Bibliography: | http://dx.doi.org/10.1073/pnas.1305885110 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Author contributions: P.P.L. and H.C.B. designed research; P.P.L. performed research; P.P.L., B.G.H., and H.C.B. contributed new reagents/analytic tools; P.P.L. and B.G.H. analyzed data; and P.P.L. and H.C.B. wrote the paper. Edited by David DeRosier, Brandeis University, Waltham, MA, and approved June 10, 2013 (received for review March 28, 2013) |
ISSN: | 0027-8424 1091-6490 |
DOI: | 10.1073/pnas.1305885110 |