Applying torque to the Escherichia coli flagellar motor using magnetic tweezers

The bacterial flagellar motor of Escherichia coli is a nanoscale rotary engine essential for bacterial propulsion. Studies on the power output of single motors rely on the measurement of motor torque and rotation under external load. Here, we investigate the use of magnetic tweezers, which in principle allow the application and active control of a calibrated load torque, to study single flagellar motors in Escherichia coli. We manipulate the external load on the motor by adjusting the magnetic field experienced by a magnetic bead linked to the motor, and we probe the motor's response. A simple model describes the average motor speed over the entire range of applied fields. We extract the motor torque at stall and find it to be similar to the motor torque at drag-limited speed. In addition, use of the magnetic tweezers allows us to force motor rotation in both forward and backward directions. We monitor the motor's performance before and after periods of forced rotation and observe no destructive effects on the motor. Our experiments show how magnetic tweezers can provide active and fast control of the external load while also exposing remaining challenges in calibration. Through their non-invasive character and straightforward parallelization, magnetic tweezers provide an attractive platform to study nanoscale rotary motors at the single-motor level

Polarized operation of Yb:YAl₃(BO₃)₄ CW and mode-locked lasers

We present a diode-pumped Yb³⁺: YAl₃(BO₃)₃ (Yb:YAB) laser system and measured the polarized outputs of the CW and femtosecond mode-locked lasers with semiconductor saturable-absorber mirrors (SESAM) at the fundamental wavelength. For the CW output, polarization ratios were 88.1% and 87.2% . For the mode-locked system, polarization ratio reached 38.5%.5 page(s

Cavity design of a Yb:YAl3(BO3)4 Kerr lens mode-locked laser

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Strand separation establishes a sustained lock at the Tus-Ter replication fork barrier

The bidirectional replication of a circular chromosome by many bacteria necessitates proper termination to avoid the head-on collision of the opposing replisomes. In Escherichia coli, replisome progression beyond the termination site is prevented by Tus proteins bound to asymmetric Ter sites. Structural evidence indicates that strand separation on the blocking (nonpermissive) side of Tus-Ter triggers roadblock formation, but biochemical evidence also suggests roles for protein-protein interactions. Here DNA unzipping experiments demonstrate that nonpermissively oriented Tus-Ter forms a tight lock in the absence of replicative proteins, whereas permissively oriented Tus-Ter allows nearly unhindered strand separation. Quantifying the lock strength reveals the existence of several intermediate lock states that are impacted by mutations in the lock domain but not by mutations in the DNA-binding domain. Lock formation is highly specific and exceeds reported in vivo efficiencies. We postulate that protein-protein interactions may actually hinder, rather than promote, proper lock formation

Passively mode-locked, self-frequency doubled, diode-pumped Yb:YAl3(BO3)4 laser

We report a self-frequency doubled Yb:YAl3(BO3)4 laser mode-locked by an ion implanted SESAM. Smooth tuning from the sub-picosecond to picosecond pulsewidth regime was achieved by varying the crystal angle with a maximum average green power of 270 mW.3 page(s

Love Methods Week 2024

LoveMethodsWeek 2024 took place from January 29th to February 2nd, 2024 with events and workshops. Here we share presentations and material from the events