skip to Main Content

Suddenly I See: How Microscopes Made Microbiology Possible

“…with the aid of microscopes, there is nothing so small that escapes our investigation; therefore, there is a new visible world uncovered to understanding. -Robert Hooke, 1665

After more than 2 years of constant media coverage of the viral pandemic, it’s easy to forget that we didn’t even know microorganisms, invisible to the naked eye, existed until the mid-17th century. Although the possibility of their existence was debated as early as the 6th century BC, the direct observation of microorganisms under the microscope was essential for the foundation of the field of microbiology, which gave rise to astonishing and important discoveries.

The story begins with Robert Hooke, a British scientist well known for his discoveries spanning physics, astronomy, and paleontology. He also coined the term “cell” and was the first to publish a depiction of a microorganism – a microfungus which he observed with his microscope and documented in his book. micrography (1665). Hooke’s work paved the way for others to continue to innovate in the nascent field of microscopy.

The father of microbiology and his contemporaries

Van Leeuwenhoek’s illustrations of duckweed “animalcules”.

A decade after the publication of micrography, Antonie van Leeuwenhoek, a Dutch scientist often called the “father of microbiology”, became the first to observe bacteria under a microscope. His pioneering work in microscopy built on that of Robert Hooke and helped establish microbiology as a legitimate scientific discipline during the Dutch Golden Age of Science that lasted from the 17th century.

Stimulated by an interest in lentil-making, van Leeuwenhoek observed what he called “diertjes”, or “little animals”, in the water of the ponds. He then documented the appearance of other tiny structures and organisms, including muscle fibers, bacteria and red blood cells, using microscopes he designed and built himself. Although he made at least 25 single-lens scopes, only 9 survived. They could magnify up to 275 times, an incredible feat for their time; Hooke’s microscope was capable of approximately 50 times magnification.

One of Van Leeuwenhoek's microscopes.
One of Van Leeuwenhoek’s microscopes.

Van Leeuwenhoek’s microscopes were much smaller than those we use today and simple in design. Most consisted of a small lens clamped between 2 flat metal plates, with the complete device measuring about an inch in diameter and 2 inches in length. The specimen was placed on a spindle whose distance from the lens could be adjusted with 2 screws. This basic mode of specimen adjustment is still used in some microscopes today, although developments have occurred in all other respects.

Van Leeuwenhoek never reported his findings in a scientific journal because scientific publishing as we know it today did not exist in the 17th century. Instead, he received publication of some of his hundreds of letters submitted by the Royal Society of London. The first of these letters concerned sightings of lice, mold and bees. However, when he wrote to the Royal Society about his first sightings of single-celled organisms in late 1676, his reputation was called into question, as no one knew such organisms even existed. Fortunately, van Leeuwenhoek persisted in writing to the Society, and eventually his findings were widely accepted and even celebrated during his lifetime.

Although van Leeuwenhoek gets credit for first observing and documenting bacteria, others had hypothesized their existence hundreds of years earlier. Jain scriptures dated as early as the 6th century BC propose the existence of “nigodas”, tiny creatures living everywhere, including in the tissues of plants and animals. As we now know, that’s not far from the truth. Scientists around the world have also speculated that infectious diseases may be caused by invisible agents. The 14th century Turkish scientist Akshamsaddin described them as “seeds so small that they cannot be seen, but are alive”.

In fact, some claim that a Jesuit priest may have been the first to observe microorganisms, before Hooke or van Leeuwenhoek. Thanks to his work on projection, Athanasius Kircher was also familiar with lenses; in 1646, he wrote that milk and vinegar “abound in an innumerable multitude of worms”. Following a microscopic examination of the blood of plague victims, he also hypothesized that the plague was caused by a microorganism, although he most likely observed blood cells rather than bacteria. Yersinia pestisthe bacteria responsible.

Once microorganisms were discovered, the field of microbiology was free to flourish. And it flourished – the 19th century, in particular, was replete with microbiological discoveries, from Louis Pasteur’s refutation of the spontaneous generation theory, to Robert Koch’s germ theory and the recognition that hand washing could prevent infections in medical practice.

Optical and fluorescence microscopy

Microscopes themselves have come a long way since van Leeuwenhoek’s handmade lenses. Nevertheless, optical microscopy remains a fundamental technique used in many laboratories to observe the shapes and behaviors of microorganisms. Light microscopes are also used for applications such as diagnosing bacterial and fungal infections in resource-limited settings without access to PCR-based testing. However, light microscopy ultimately only allows scientists to view cells as they appear in natural light.

Thanks to the invention of fluorescence microscopy at the beginning of the 20th century, we can use fluorescent marker genes or dyes to highlight different types of cells, or focus on cellular components. For example, green fluorescent protein (GFP), an isolated fluorescent protein originally from a glowing jellyfish, is often attached to specific proteins. This allows scientists to track their movements within or between cells. The developers of GFP in such a tool – Martin Chalfie, Osamu Shimomura and Roger Y. Tsien – were awarded the Nobel Prize in Chemistry in 2008. GFP can be harnessed for all sorts of applications, from monitoring cancer cell metastasis to measuring the toxicity of pollutants and even investigating how axolotls regrow their limbs.

Section of mouse hippocampus, with GFP-labeled neurons.
Section of mouse hippocampus, with GFP-labeled neurons.

Electron microscopy

The magnification power of microscopes has increased dramatically since the tool was first invented – today the maximum magnification of optical microscopes, imposed by the physical limits of visual light, is around 1,000 times. This magnification is sufficient to clearly observe eukaryotic and bacterial cells, as they measure between 1 and 100 micrometers (µm) in diameter. While different types of electron microscopes achieve resolutions as small as 1 nanometer (nm), one-thousandth of 1 µm), providing extremely precise insight into the smallest of structures, including viruses and even individual atoms.

“We only perceive the part of nature that our technologies allow, and likewise our theories about nature are severely limited by what our technologies allow us to observe.” – Gilbert et al., 2012

Electron microscopy was invented in 1931 by a team of 2 German scientists, Ernst Ruska and Max Knoll. They realized that the physical limitations of light microscopy could be overcome if an electron beam, instead of a photon beam, was fired at the subject. Transmission electron microscopy (TEM), invented by Ruska and Knoll, and scanning electron microscopy (SEM), an elaboration of TEM, are used in scientific fields ranging from geology to life sciences and electrical engineering . SEM allows scientists to see the surface of their sample in 3D; classic examples of SEM images include close-ups of pollen grains and bed bugs that are often featured in science magazines. Meanwhile, TEM is used for structural analyzes of very thin 2D sample slices and can be used to visualize cross sections of cells and whole organisms.

Pollen seen using a scanning electron microscope (pseudocolor).
Pollen seen using a scanning electron microscope (pseudocolor).

Elaborations on this technique, such as cryogenic electron microscopy (cryo-EM), can provide even more information, allowing scientists to visualize cellular structures in their 3D contexts. Cryo-EM uses cryogenic freezing, in which samples are frozen in liquid nitrogen, to preserve protein structure. This avoids the need to crystallize proteins, which was a major limitation for studying certain types of proteins, such as those embedded in cell membranes. For example, cryo-EM has allowed scientists to reconstruct the structure of SARS-CoV-2’s spike protein at atomic resolution and determine how changes in its structure allow the virus to evade cell-based immunity. the vaccine. The technique’s developers, Jacques Dubochet, Joachim Frank and Richard Henderson, were awarded the Nobel Prize in Chemistry in 2017, demonstrating its value to modern science.

In addition to allowing us to learn more about living organisms, microscopes have also enabled advances in nanotechnology. For example, the discovery of carbon nanotubes, reported in 1991, was made possible by electron microscopy. These pure carbon tubular structures, only a few nanometers wide, can have excellent conductivity and tensile strength, making them attractive for many engineering uses in materials science and microelectronics.

new technics ; New Horizons

Although clever thinkers postulated that microbes existed centuries before, the invention of microscopes and the insights these tools provided about a world invisible to the naked eye was key to launching the broader study of microbes. organisms. In the recent words of Dr. Dave Ng, a teaching professor at the University of British Columbia, “new ways of knowing lead to new ways of thinking”; with each advancement in microscopy techniques and technologies, we learn something new about the world around us, no matter how small.

Back To Top