Timing the Start of Division in E. coli: a Single-Cell Study

Abstract

Flagella and cilia play a critical role in eukaryotic cell motility. Among the most notable waveforms exhibited by eukaryotic flagella are planar and helical waves observed in mammalian sperm and protozoa. Here we report on a highspeed study of the flagellar motility of the protozoan parasite Trypanosoma brucei responsible for the African sleeping sickness whose vector is the tsetse fly. In this organism, the flagellum is physically attached along the length of the tapering cell body, unlike the case of mammalian sperm where the flagellum is attached to the body only at one attachment site. Earlier studies had reported that propulsion was driven by helical waves propagating from the flagellar tip to the base with left-handed helicity. Using a millisecond-timescale microscope, we discovered a novel form of eukaryotic cell motility, in which alternating left-handed and right-handed helical waves (termed ''bihelical waves'') propagate along the flagellum and are separated by a moving kink. These bihelical waves produce torsion in the cell body that is resolved by a rocking motion but -unlike the case of mammalian sperm or the existing model for T. bruceiwithout net rotation. We also observed the rapid motion of the flagellum tip, for which we recorded velocities up to 673 nm/ms, about 96 times greater than the velocity of dynein motors in vivo. The forward translational movement of the body is coupled to both the rocking of the posterior cell body about its own axis and the axis of locomotion as well as the propagation of the bihelical waves and kinks. Our results demonstrate that millisecond-timescale microscopy is essential for studies of cell locomotion in microorganisms.

Threshold effect of growth rate on population variability of Escherichia coli cell lengths

“…We followed the growth dynamics of single cells, as they formed microcolonies at 37°C on LB agar for 140 min (figure 3 a ; electronic supplementary material, video S4). Consistent with previous reports of growth rate heterogeneity in single cells [48], we find that growth rates vary in the range of 0.6–2.3 h −1 in the population (figure 3 b ). Each colony examined originates from a single cell, and hence at the end of 140 min when microcolony sizes vary, the cell–cell variation in growth rates is confirmed.…”

Defining the rate-limiting processes of bacterial cytokinesis

“…Previous attempts to measure time-dependent changes in septum closure rates produced mixed results, likely because different stages of the constriction process were examined (78,79). Using PALM, we could not measure the time dependence of septum closure rate directly because prolonged imaging of the same cell leads to phototoxicity and is thus unreliable.…”

“…3 I-K, solid curves), indicating that, on average, septum closure accelerates in these cells. Additionally, the hemispherical geometry of the growing septum in wild-type (wt) E. coli dictates that an α value of <2 corresponds to deceleration in the growth of septal surface area during constriction (78). Therefore, in wt BW25113 grown in M9 at RT, the rate of septum diameter closure during constriction accelerates, whereas the addition of septum surface area per unit time gradually decreases.…”

Growth, metabolic partitioning, and the size of microorganisms

“…At one end of this spectrum, experimental techniques are expanding our ability to track single cells through a division cycle, revealing the growth trajectories of individual organisms even at the microbial scale ( Fig. 1) (7)(8)(9)(10)(11)(12). At the population scale, single-species culture studies have been used to understand the relationship between resource use and growth rate (13)(14)(15)(16)(17)(18).…”

“…We compare the underlying bioenergetics of different species, as represented by the parameters of our framework, using these fits along with separate estimates obtained from growth-resource consumption data for populations of cells. We compiled published measurements of the size of single cells as they grow through a division cycle for five species, including the heterotrophic bacteria Escherichia coli (8,9) and Bacillus subtilis (7), two photo-autotrophic marine diatoms (Thalassiosira weissflogii and Lauderia borealis) (10), as well as budding yeast Candida albicans (11). In addition, we used growth data for individuals from two small (submillimeter), multicellular marine copepods (Calanus pacificus and Pseudocalanus sp.)…”