How is microorganism discovered

The discovery of viruses

If you want to discover them, you have to look carefully

In 1883 the German researcher Adolf Mayer laid the foundation stone. The microbiologist is studying a disease that tobacco plants suffered from. He suspects that bacteria are causing the suffering.

Because the strange disease can be transmitted, that's for sure. Whenever Mayer sprays healthy tobacco plants with the cell sap of diseased plants, these also show the symptoms.

A mosaic pattern runs through the leaves. In addition, the diseased specimens develop a compressed growth. A previously unknown substance has to do mischief in the cell sap. But which ones?

The researcher cannot see anything under the light microscope. At least not what he's looking for: bacteria. Mayer suspects that the carriers of the disease must be even smaller. Maybe they are tiny bacteria, smaller than the ones we already know. He writes down his hypothesis, but does not pursue it any further.

Is it a germ or a poison?

Ten years later, a scientist from Russia sets out to check Mayer's conjecture. Dimitri Iwanowski lets the cell sap of infected plants run through a special bacterial filter.

However, he cannot detect any bacteria in the filter. The cell sap remains infectious. Ivanovsky sticks to the hypothesis of his colleague Mayer, but he also thinks a poison is possible.

In 1897 a scientist from the Netherlands refuted this approach: Martinus Beijerinck sprayed a healthy plant with the cell sap of infected specimens. The result: the cell sap of the sprayed plant is also infectious. He proves this by spraying another plant and repeating the series.

However, the pathogen does not weaken. The dose of a poison should always have been reduced. But this pathogen seems to reproduce and does not lose its effectiveness. Poison couldn't do that.

Beijerinck researched further and found that the disease-causing substance can only reproduce within organisms. Neither in the Petri dish nor in the test tube does what bacteria otherwise effortlessly do.

Many bacteria can be fought with alcohol - but this unknown substance is resistant to it. Beijerinck imagines something infectious that must be much smaller and simpler than a bacterium.

After more than 50 years, the researchers found what they were looking for

In 1935, the American Wendell M. Stanley finally confirmed the assumption made by his Russian colleague. After more than 50 years of exhausting search, the researcher succeeds in isolating the infectious particle.

After a series of tests, his extract from tobacco plants contains the finest crystal needles that are barely visible under the light microscope.

Although the tiny needles show no metabolic activity, they remain highly infectious. Stanley uses the Latin word for poison for the structure: "virus". While he cannot yet know that every needle is made up of a large number of viruses, his conclusions remain correct.

When the first electron microscope (EM) was developed in 1940, Stanley's hypothesis was confirmed. Even more: the EM can now be used to detect and research other viruses.

In 1946 Stanley received the Nobel Prize in Chemistry. The tobacco mosaic virus goes down in history. And with it the global cooperation that ultimately led to the goal. It is still essential to this day that international research teams work together to research viruses - because viruses do not know national borders.