Flagellar Motor Remodeling and Filament Growth

Abstract

As symposium chair, I will tell you a few things about bacterial motility that E. coli knows, and then describe two recent vignettes, involving adaptation at the output of the sensory-transduction pathway, and growth of flagellar filaments. 1) Receptor methylation and demethylation are required for adaptation on the second time scale, which enables cells to make temporal comparisons and swim up spatial gradients of attractants. In the absence of the methyltransferase and the methylesterse, one still observes partial adaptation, on the minute time scale. The motor shifts its operating point to accommodate new steady-state levels of the response regulator CheY-P. When the concentration of CheY-P decreases, the motor spins CCW and the number of copies of the protein to which CheY-P binds, FliM, increases, partially restoring motor sensitivity. 2) Flagellar filaments grow at their distal ends. The dogma in the field asserts that they do so at a rate that decreases exponentially with length. By labeling filaments twice, first with a green fluorescent dye and later with a red fluorescent dye, we find that filaments grow at a constant rate. On average, the lengths of red segments do not depend upon the lengths of green segments from which they grew.