Nov 16, 2018 | |
Scientists produce 3D nanoscale chemical maps of single bacteria(Nanowerk News) Scientists at the National Synchrotron Light Source II (NSLS-II)--a U.S. Department of Energy (DOE) Office of Science User Facility at DOE's Brookhaven National Laboratory--have used ultrabright x-rays to image single bacteria with higher spatial resolution than ever before. |
|
Their work, published in Scientific Reports ("X-ray Fluorescence Nanotomography of Single Bacteria with a Sub-15 nm Beam"), demonstrates an x-ray imaging technique, called x-ray fluorescence microscopy (XRF), as an effective approach to produce 3-D images of small biological samples. | |
A 3-D view of the single bacteria produced through XRF. | |
"For the very first time, we used nanoscale XRF to image bacteria down to the resolution of a cell membrane," said Lisa Miller, a scientist at NSLS-II and a co-author of the paper. "Imaging cells at the level of the membrane is critical for understanding the cell's role in various diseases and developing advanced medical treatments." | |
The record-breaking resolution of the x-ray images was made possible by the advanced capabilities of the Hard X-ray Nanoprobe (HXN) beamline, an experimental station at NSLS-II with novel nanofocusing optics and exceptional stability. | |
"HXN is the first XRF beamline to generate a 3-D image with this kind of resolution," Miller said. | |
While other imaging techniques, such as electron microscopy, can image the structure of a cell membrane with very high resolution, these techniques are unable to provide chemical information on the cell. At HXN, the researchers could produce 3-D chemical maps of their samples, identifying where trace elements are found throughout the cell. | |
"At HXN, we take an image of a sample at one angle, rotate the sample to the next angle, take another image, and so on," said Tiffany Victor, lead author of the study and a scientist at NSLS-II. "Each image shows the chemical profile of the sample at that orientation. Then, we can merge those profiles together to create a 3-D image." | |
Miller added, "Obtaining an XRF 3-D image is like comparing a regular x-ray you can get at the doctor's office to a CT scan." | |
The images produced by HXN revealed that two trace elements, calcium and zinc, had unique spatial distributions in the bacterial cell. | |
XRF images show the zinc (B), calcium (C), chlorine (D) distributions in the single bacteria. XRF image E shows all three elements in the cell. Image A shows bacteria embedded in sodium chloride crystals. | |
"We believe the zinc is associated with the ribosomes in the bacteria," Victor said. "Bacteria don't have a lot of cellular organelles, unlike a eukaryotic (complex) cell that has mitochondria, a nucleus, and many other organelles. So, it's not the most exciting sample to image, but it's a nice model system that demonstrates the imaging technique superbly." | |
Yong Chu, who is the lead beamline scientist at HXN, says the imaging technique is also applicable to many other areas of research. | |
"This 3-D chemical imaging or fluorescence nanotomography technique is gaining popularity in other scientific fields," Chu said. "For example, we can visualize how the internal structure of a battery is transforming while it is being charged and discharged." | |
In addition to breaking the technical barriers on x-ray imaging resolution with this technique, the researchers developed a new method for imaging the bacteria at room temperature during the x-ray measurements. | |
"Ideally, XRF imaging should be performed on frozen biological samples that are cryo-preserved to prevent radiation damage and to obtain a more physiologically relevant understanding of cellular processes," Victor said. "Because of the space constraints in HXN's sample chamber, we weren't able to study the sample using a cryostage. Instead, we embedded the cells in small sodium chloride crystals and imaged the cells at room temperature. The sodium chloride crystals maintained the rod-like shape of the cells, and they made the cells easier to locate, reducing the run time of our experiments." | |
The researchers say that demonstrating the efficacy of the x-ray imaging technique, as well as the sample preparation method, was the first step in a larger project to image trace elements in other biological cells at the nanoscale. The team is particularly interested in copper's role in neuron death in Alzheimer's disease. | |
"Trace elements like iron, copper, and zinc are nutritionally essential, but they can also play a role in disease," Miller said. "We're seeking to understand the subcellular location and function of metal-containing proteins in the disease process to help develop effective therapies." |
Source: Brookhaven National Laboratory | |
Subscribe to a free copy of one of our daily Nanowerk Newsletter Email Digests with a compilation of all of the day's news. |