34 research outputs found
Multiflagellarity leads to the size-independent swimming speed of bacteria
Flagella are essential organelles of bacteria enabling their swimming
motility. While monotrichous or uniflagellar bacteria possess a single
flagellum at one pole of their body, peritrichous bacteria grow multiple
flagella over the body surface, which form a rotating helical bundle propelling
the bacteria forward. Although the adaptation of bacterial cellular features is
under strong evolutionary pressure, existing evidence suggests that
multiflagellarity confers no noticeable benefit to the swimming of peritrichous
bacteria in bulk fluids compared with uniflagellar bacteria. This puzzling
result poses a long-standing question: why does multiflagellarity emerge given
the high metabolic cost of flagellar synthesis? Contrary to the prevailing
wisdom that its benefit lies beyond the basic function of flagella in steady
swimming, here we show that multiflagellarity provides a significant selective
advantage to bacteria in terms of their swimming ability, allowing bacteria to
maintain a constant swimming speed over a wide range of body size. By
synergizing experiments of immense sample sizes with quantitative hydrodynamic
modeling and simulations, we reveal how bacteria utilize the increasing number
of flagella to regulate the flagellar motor load, which leads to faster
flagellar rotation neutralizing the higher fluid drag on their larger bodies.
Without such a precise balancing mechanism, the swimming speed of uniflagellar
bacteria generically decreases with increasing body size. Our study sheds light
on the origin of multiflagellarity, a ubiquitous cellular feature of bacteria.
The uncovered difference between uniflagellar and multiflagellar swimming is
important for understanding environmental influence on bacterial morphology and
useful for designing artificial flagellated microswimmers.Comment: 23 pages, 4 figure
A plausible method of preparing the ideal p-n junction interface of a thermoelectric material by surface doping
Recent advances in two-dimensional (2D) crystals make it possible to realize
an ideal interface structure that is required for device applications.
Specifically, a p-n junction made of 2D crystals is predicted to exhibit an
atomically well-defined interface that will lead to high device performance.
Using angle-resolved photoemission spectroscopy, a simple surface treatment was
shown to allow the possible formation of such an interface. Ta adsorption on
the surface of a p-doped SnSe shifts the valence band maximum towards higher
binding energy due to the charge transfer from Ta to SnSe that is highly
localized at the surface due to the layered structure of SnSe. As a result, the
charge carriers of the surface are changed from holes of its bulk
characteristics to electrons, while the bulk remains as a p-type semiconductor.
This observation suggests that the well-defined interface of a p-n junction
with an atomically thin {\it n}-region is formed between Ta-adsorbed surface
and bulk.Comment: 4 figure
Fixed-Target Pink-Beam Serial Synchrotron Crystallography at Pohang Light Source II
Serial crystallography (SX) enables the determination of the structure of macromolecules or small molecules with minimal radiation damage. In particular, biomolecule structures determined using the SX technique have the advantage of providing room-temperature crystal structures with high biological relevance. The SX technique requires numerous crystals to be collected to complete three-dimensional structural information. To minimize crystal sample consumption, we introduced SX data collection with fixed-target (FT) pink-beam serial synchrotron crystallography (SSX) at the 1C beamline of Pohang Light Source II. A new sample holder consisting of a magnetic frame with a nylon mesh was developed for easy sample handling. The FT-pink-SSX diffraction data were collected by continuously scanning X-rays using a stepping motor. The room-temperature structures of glucose isomerase and lysozyme were successfully determined at a resolution of 1.7 and 2.2 Å, respectively. The use of pink-beam FT-SSX in experimental applications and data acquisition for large beam sizes is discussed. Our results provide useful information for future pink-beam SSX and SX data collection using large X-ray beams
Room-temperature structure of lysozyme by fixed-target pink-beam serial synchrotron crystallography
Title: Room-temperature structure of lysozyme by fixed-target pink-beam serial synchrotron crystallography
Data: Hit images
Depositors: Yongsam Kim and Ki Hyun Nam
Synchrotron: Pohang Light Source II
Beamline: 1C
Technique: Fixed-target pink-beam serial synchrotron crystallograph
Room-temperature structure of glucose isomerase by fixed-target pink-beam serial synchrotron crystallography
Title: Room-temperature structure of glucose isomerase by fixed-target pink-beam serial synchrotron crystallography
Data: Hit images
Depositors: Yongsam Kim and Ki Hyun Nam
Synchrotron: Pohang Light Source II
Beamline: 1C
Technique: Fixed-target pink-beam serial synchrotron crystallograph
Data of pink-beam serial synchrotron crystallography at the Pohang Light Source II
Serial synchrotron crystallography (SSX) helps to determine the room-temperature structure of macromolecules with minimal radiation damage. Pink-beam X-ray provides more photon flux than a monochromatic beam, which can increase the diffraction intensity of crystal samples and reduce the issue of partial reflection measurement compared with a monochromatic beam. The demonstration of pink-beam SSX at the 1C beamline at the Pohang Light Source II (PLS-II) was previously reported. The Bragg peaks observed in SSX diffraction data using a pink-beam exhibited a slightly stretched shape, unlike that from a monochromatic beam. Therefore, it is necessary to develop an indexing algorithm that can efficiently process the Bragg peak generated by pink-beam SSX. Therefore, the collected pink-beam SSX diffraction data can be tentatively used to develop an indexing program for Bragg peaks generated using the pink-beam. In this study, detailed information on the diffraction data of pink-beam SSX at PLS-II was reported to access the raw data and process the information
Pink-Beam Serial Synchrotron Crystallography at Pohang Light Source II
Serial crystallography (SX) enables the determination of room-temperature structures with minimal radiation damage. The photon flux of the pink beam of 1.2% bandwidth (BW) is one order higher than that of the monochromatic beam from a silicon crystal monochromator, and the energy resolution of 1.2% BW is enough to solve the structure; therefore, it is useful to use the pink beam for time-resolved serial synchrotron crystallography (SSX). Here, we demonstrate a pink-beam serial synchrotron crystallographic study at the 1C beamline at the Pohang Light Source II. Lysozyme crystals embedded in a beef tallow injection matrix were delivered through a syringe into the X-ray interaction point. Pink-beam SSX was performed with different X-ray exposure positions to the injection stream (center and edge) and X-ray exposure times (50 and 100 ms). All lysozyme crystal structures were successfully determined at a high resolution of 1.7 Å. Background analysis showed that X-ray diffraction data exposed to the edge of the injection stream could improve the signal-to-noise ratio. All the diffraction data and room-temperature lysozyme structures were comprehensively compared. The data collection strategy and analysis will be helpful in further pink-beam SSX experiments and their applications