A simple platform for in situ DNA-PAINT optimization enables improved multiplexed super-resolution imaging in Gram-negative bacteria
This study establishes an RNA-FISH-based screening platform to systematically optimize DNA-PAINT imager-docking pairs within intact Gram-negative bacteria, enabling high-quality, multiplexed 3D super-resolution imaging of bacterial structures and RNA clusters.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Bacteria are incredibly small, microscopic cities where life's most fundamental processes happen on a scale so tiny that ordinary light microscopes cannot see them. To understand how these single-celled organisms organize their DNA, build their walls, or send out proteins, scientists need to see details that are far smaller than the wavelength of visible light. For years, researchers have developed special techniques to bypass this limit, allowing them to visualize the inner workings of cells with stunning clarity. One such method, known as DNA-PAINT, uses short strands of genetic material that act like tiny, blinking lighthouses. These strands float around and briefly attach to specific targets inside the cell, flashing a light each time they bind before detaching again. By recording thousands of these fleeting flashes, a computer can piece together a precise map of where molecules are located, revealing structures with a resolution of just a few nanometers. While this technique has been a powerful tool for studying larger human cells, it has been difficult to use inside bacteria. The bacterial cell wall is a tough, complex barrier, and the crowded interior makes it hard for the necessary chemical tools to work effectively. Without a reliable way to test which chemical combinations work best inside these tiny organisms, the technique has remained largely unused in the study of bacteria.
A team of researchers has now built a simple, practical platform to solve this problem, opening the door for high-resolution imaging inside Gram-negative bacteria like E. coli and Yersinia enterocolitica. The scientists realized that to make DNA-PAINT work inside a bacterium, they first needed a way to test and tune the chemical "keys" that unlock the imaging process. They created a screening system based on a well-known probe that targets ribosomes, the protein-making machines found in every bacterial cell. By attaching different DNA-PAINT docking sequences to this probe, they could test how well various chemical pairs performed inside the actual bacterial environment. They tested twelve different sequences, measuring how specifically they bound to their targets, how bright they flashed, and how long they stayed attached. This process allowed them to identify the best-performing combinations and fine-tune the imaging settings, such as how long the camera should wait between photos, to capture the clearest possible images.
The results of this optimization were immediate and transformative. Using the best-performing sequences, the researchers successfully created four-color, three-dimensional maps of a single E. coli cell. They visualized the outer membrane, the inner membrane, the bacterial DNA, and the machinery that reads genetic instructions, all at the same time. The images were sharp enough to measure the tiny gap between the inner and outer membranes, revealing a space of about 51 nanometers. This level of detail confirmed that the technique could distinguish between structures that are separated by only a few tens of nanometers, a feat that was previously impossible with standard methods. The team also applied their optimized system to a pathogenic bacterium, Yersinia enterocolitica, which causes illness in humans. They mapped the locations of three different messenger RNA molecules that carry instructions for making virulence proteins. The images showed that these genetic messages were not randomly scattered but were clustered in specific areas of the cell, mostly near the poles, providing new insights into how the bacteria organize their infection machinery.
This work establishes a straightforward, cost-effective framework for other scientists to adopt these advanced imaging techniques. By providing a method to systematically test and improve the chemical tools needed for DNA-PAINT inside bacteria, the researchers have removed a major barrier to entry. The study demonstrates that with the right conditions, it is possible to see the molecular architecture of bacteria with near-molecular precision. The findings suggest that the long-held view of bacteria as simple, uniform bags of chemicals is incorrect; instead, they possess a highly organized internal structure that can now be visualized in three dimensions. This new capability promises to accelerate the understanding of bacterial physiology and the mechanisms of infection, offering a clearer view of the microscopic world that has long been hidden from sight.
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