Bacterial photoshoot: In X-ray light

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  • Published: Feb 15, 2015
  • Author: David Bradley
  • Channels: X-ray Spectrometry
thumbnail image: Bacterial photoshoot: In X-ray light

Molecular machinery

The first ever X-ray free-electron laser portraits of living cyanobacteria captured by an international team of scientists at SLAC could represent a step towards the exploration of the molecular machinery at work in viral infections, cell division, photosynthesis and other important processes. Credit: SLAC National Accelerator Laboratory

The first ever X-ray free-electron laser portraits of living cyanobacteria captured by an international team of scientists at SLAC could represent a step towards the exploration of the molecular machinery at work in viral infections, cell division, photosynthesis and other important processes. 

Theory predicts "diffraction before destruction" in which an ultra-short and extremely bright coherent X-ray pulse from an X-ray laser can outrun radiation-induced damage processes so that a molecular-level snapshot of a large macromolecule, a virus, or a cell might be obtained.

"We have developed a unique way to rapidly explore, sort and analyze samples, with the possibility of reaching higher resolutions than [possible with] other study methods," explains biophysicist Janos Hajdu of Uppsala University in Sweden. "This could eventually be a complete game-changer."

The team carried out a proof principle experiment with cyanobacteria, also known as blue-green algae. These organisms are abundant and are thought to have transformed Earth's atmosphere 2.5 billion years ago by releasing oxygen through photosynthesis. Cyanobacteria, today, play a critical role in the planet's oxygen, carbon and nitrogen cycles to this day.

Imaging spray

Exposing a humid spray of live cyanobacteria in a thin stream with no pre-treatment, to ultrabright, ultrashort X-ray pulses produces usable diffraction data, the team has now shown. The diffraction patterns preserved details of the cyanobacteria that can then be composited to form a two-dimensional image at the moment, giving the team synthetic phase-contrast (X-ray Nomarski) images calculated from the complex-valued reconstructions. 3D images should ultimately be possible using the same technique. The team says that they capture approximately 100 images per second and so amassing millions of high-resolution X-ray images in a single day. This high throughput rate lets them sort and analyse the inner structure and activity of biological particles on an unprecedented scale, with the potential to show "time lapse" sequences of changes occurring at the cellular level.

Other researchers have used optical microscopy and X-ray tomography to obtain high-resolution 3D images of living cells, but this new approach takes the resolution to the nanometre level. Tomas Ekeberg suggests that this approach merges biology and big data: "You can study the full cycle of cellular processes, with each X-ray pulse providing a snapshot of the process you want to study," he explains. The approach might then be used to reveal the differences and similarities between groups of cellular structures and to show how these structures interact: What is in the cell? How is it organized? How is it communicating?

Improvers

The researchers are now improving the technique and upgrading instrumentation as part of the Linac Coherent Light Source (LCLS) Single-Particle Imaging initiative, an international effort launched at SLAC in October 2014. The initiative hopes to make atomic-scale imaging available for many different classes of biological sample, including living cells.

Also involved in the X-ray work were scientists from the Lawrence Berkeley National Laboratory, DESY, the European XFEL, PNSensor, the Max Planck Institute for Extraterrestrial Physics and the University of Hamburg, in Germany, the University of Rome Tor Vergata, the University of Melbourne, Australia, Kansas State University and the National University of Singapore.

Related Links

Nature Commun 2015, 6, 5704: "Imaging single cells in a beam of live cyanobacteria with an X-ray laser"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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