Martinus Beijerinck

Chapter 1 · Twenty Years Before a Laboratory

A failed tobacco business, a yeast factory, and a difficult man

1851 – 1895 · Amsterdam · Delft · Leiden · Wageningen

Martinus Willem Beijerinck was born in Amsterdam in March 1851. His father was a tobacco dealer whose business failed — a detail worth holding, because tobacco is how the plant that made him famous entered his life at all.

He trained at the Polytechnic at Delft and took a doctorate at Leiden. And then, for twenty years, he did not get the position his ability warranted.

He taught at an agricultural school at Wageningen. He worked as a microbiologist for the Netherlands Yeast and Spirit Factory at Delft — industrial work, on fermentation. Only in 1895, at forty-four, was he made professor at the Delft Polytechnic, with a laboratory of his own.

Part of this was circumstance. Part of it was him. Beijerinck was, by consistent report, difficult: severe, sarcastic with students, unsociable, and intolerant of imprecision in a way that shaded into contempt. He never married, and his sister Henriette kept house for him. He is said to have regarded marriage as incompatible with science and to have discouraged his assistants from it.

What he built in those years was a *method*. The *enrichment culture* inverts the usual approach: rather than growing everything and trying to pick out what you want, you set the conditions — the food source, the gases, the salts, the temperature — so that *only* the organism you are hunting can survive and multiply in them. Then you wait, and it presents itself.

It is still the standard way of isolating an unknown microbe.

Why this matters

The enrichment culture — set conditions only your target can survive, then wait — is still how an unknown micro-organism is isolated.

You have the twenty years and the method built in them. What would you ask?

Ask Beijerinck

• “How does an enrichment culture actually work?”
• “Why did it take twenty years to get a laboratory?”
• “Were you as difficult as people said?”
• “What did industrial work at a yeast factory teach you?”
• “Is it true you thought marriage incompatible with science?”

Chapter 2 · The Microbes That Run the Soil

Nitrogen fixation, and the cycles nobody had attributed to organisms

1888 – 1901 · Wageningen · Delft

Before the famous virus work, Beijerinck did something arguably as important: he showed that the great chemical cycles of the soil are run by micro-organisms.

In 1888 he isolated the bacterium living in the root nodules of leguminous plants — clover, peas, beans — and showed that it takes nitrogen gas directly from the air and converts it into compounds the plant can use. He named it *Bacillus radicicola*; it is now *Rhizobium*.

This explains something farmers had known empirically for two thousand years without understanding: that growing legumes enriches the soil, and that rotating them with cereals maintains fertility. The relationship is a partnership — the plant supplies sugars and a protected home; the bacterium supplies fixed nitrogen. Neither does it alone.

He went on to isolate free-living nitrogen-fixing bacteria in soil, and *sulphate-reducing* bacteria, which convert sulphates to sulphides and drive the sulphur cycle.

The general conclusion he drew is the one that matters: behind every chemical change in the soil there is an organism doing it. Soil chemistry is biology.

That reframing is the foundation of soil microbiology, of the nitrogen cycle as taught, and of the whole idea of biogeochemical cycles — that the composition of the planet's air, water and soil is substantially maintained by microbes.

He found all of it with the enrichment culture: build a medium with no nitrogen source but the air, and only something that can fix nitrogen will grow in it.

“Contagium vivum fluidum — a contagious living fluid.”

— Martinus Beijerinck, on the tobacco mosaic agent (1898)

Why this matters

Beijerinck showed that the chemical cycles of the soil are driven by micro-organisms, which is the foundation of the nitrogen cycle as it is taught.

You have the root nodules and the cycles they drive. What is your question?

Ask Beijerinck

• “How do you design a medium only one organism can live in?”
• “What does the plant give the bacterium in return?”
• “Why does growing clover improve a field?”
• “Is soil chemistry really just biology?”
• “Which cycle would you have gone after next?”

Chapter 3 · Something That Passed the Filter

Tobacco mosaic disease, 1898

1886 – 1898 · Delft

Tobacco mosaic disease mottles the leaves of tobacco plants and ruins the crop. Three men worked on it in sequence, and the sequence is the lesson.

Adolf Mayer showed in 1886 that sap from a diseased plant, rubbed onto a healthy one, transmits the disease. So there is an agent, and it is in the sap. He assumed a bacterium and could not find one.

Dmitri Ivanovsky in 1892 passed the sap through a Chamberland porcelain filter — a filter with pores fine enough to hold back every known bacterium, the standard test for bacterial sterility. The filtrate was *still infectious*.

Ivanovsky had the crucial result six years before Beijerinck and did not believe it. He concluded that his filter must be cracked, or that a bacterium was producing a toxin small enough to pass. He did not pursue it.

Beijerinck repeated the filtration in 1898 and got the same result. Then he did the experiments neither of the others had.

He poured the filtrate onto the top of a plate of clear agar gel and let it stand. Bacteria cannot move through agar; they sit on the surface. After some time he cut into the gel and took material from *deep inside* it — and that material was infectious. Whatever it was had *diffused* through the gel, like a dissolved substance. No bacterium could do that.

He also showed it was not a toxin. He infected a plant, took sap from *it*, and found it as potent as the original. A poison would be diluted. This was *multiplying*.

Why this matters

Ivanovsky filtered the sap six years earlier and disbelieved his own result; Beijerinck's contribution was refusing to explain away a finding that would not fit.

You have the filtrate deep in the agar. What would you ask him?

Ask Beijerinck

• “Why did the agar plate settle it?”
• “How did you rule out a bacterial toxin?”
• “Why did Ivanovsky not believe his own filter?”
• “When is a result finished?”
• “How much did Mayer and Ivanovsky contribute?”

Chapter 4 · Only Inside Something Living

The finding that defines a virus

1898 · Delft

The most important result is the one that sounds like a failure.

Beijerinck could not grow the agent. He tried every broth and medium he had — the same media in which he had cultured bacteria for twenty years — and nothing multiplied in any of them.

It would only multiply inside a *living, actively growing* plant. Not in dead plant tissue. Not in extracted sap. Not in any nutrient preparation. It needed the living, dividing cell.

That is the defining property of a virus, and Beijerinck established it. A virus is an obligate intracellular parasite: it carries no machinery for making proteins or generating energy, and can reproduce only by taking over the machinery of a host cell.

He did not know that, because he had no idea what the thing was made of. But the *behaviour* he demonstrated is exactly what that structure implies, and it is what distinguishes a virus from every bacterium.

He also showed it survived drying, survived being kept for months, and could be inactivated by heat and by alcohol.

He named it *contagium vivum fluidum* — a contagious living fluid. Every word was deliberate, and he meant *fluid* literally: he thought the agent was a liquid, a soluble substance, not a particle. The diffusion through agar seemed to him to prove it.

The word he used for it in passing — *virus*, then simply Latin for a poison or slime — became the name of the whole category.

Why this matters

That it multiplies only inside a living, dividing cell is the defining property of a virus, and Beijerinck established it experimentally in 1898.

You have the thing that would grow in nothing on the bench. What is your question?

Ask Beijerinck

• “What did you try to grow it in?”
• “Why is needing a living cell such an important finding?”
• “Why did you think it was a fluid?”
• “What made you call it living?”
• “Where did the word 'virus' come from?”

Chapter 5 · Wrong About Two Words

Not a fluid, and not alive

1898 – 1935 and after · Delft · Gorssel · Princeton

*Contagium vivum fluidum* has three ideas in it. Contagious — right. Living — contested, and by the modern reckoning wrong. Fluid — wrong.

The agent is a *particle*: a strand of RNA in a coat of protein. It diffused through agar not because it was dissolved but because it is extremely small — tobacco mosaic virus is about 300 nanometres long and 18 across, far smaller than the pore structure of the gel and than any bacterium.

Wendell Stanley crystallised it in 1935, which won him a Nobel Prize, and demonstrated something startling: it forms crystals like a chemical substance, and the crystals remain infectious. It was first *seen* in an electron microscope in 1939, forty-one years after Beijerinck described it and eight years after his death.

And it is not, by the modern account, alive. It does not respire, does not grow, does not respond to stimuli, does not metabolise, and cannot reproduce without commandeering a cell. Whether viruses count as living is still discussed and there is no settled answer, but the standard position is that they do not.

So the founder of virology named his discovery in three words and got two of them wrong, and defended the wrong ones.

What survives is everything else, and it is most of it. That the agent is not a bacterium. That it is not a poison. That it *multiplies*. That it multiplies only inside a living cell. Every one of those was established on his bench and every one is still taught.

He retired in 1921 and died at Gorssel in January 1931, aged seventy-nine, before anyone had seen the thing he found.

Why this matters

Beijerinck founded virology while being wrong about what a virus is, because his experimental findings about its behaviour did not depend on his theory of its nature.

You have the crystal, the electron micrograph and the two wrong words. What would you ask?

Ask Beijerinck

• “What would you say if I told you it was a particle?”
• “Is a virus alive?”
• “How can something crystallise and still be infectious?”
• “Which of your conclusions have survived?”
• “Does being wrong about the nature of it diminish the discovery?”

What Beijerinck changed

Beijerinck founded virology, and the findings that survive are the ones that matter: that the agent is not a bacterium, that it is not a poison, that it multiplies, and that it multiplies only inside a living dividing cell. Every one was established on his bench and every one is still taught. He also invented the enrichment culture, still the standard way of isolating an unknown microbe, and showed that the chemical cycles of the soil are run by organisms.

A debate that continues

Ivanovsky filtered the tobacco mosaic agent six years before Beijerinck and disbelieved his own result, so priority is genuinely divided. Beijerinck's own account — that the agent is a fluid and that it is alive — is wrong on both counts by the modern reckoning.

Keep exploring — ask Beijerinck

• “What would you have needed to see it?”
• “How do you decide when an explanation has been ruled out?”
• “Which of your soil organisms deserves more attention?”

Related lives

• Louis Pasteur — Father of Germ Theory
• Alexander Fleming — Discoverer of Penicillin
• Antonie van Leeuwenhoek — Who Found A World In A Drop Of Water
• Élie Metchnikoff — Discoverer of the Phagocyte

Related themes

Viruses and infection · Micro-organisms · The nitrogen cycle