Martinus Beijerinck

Who Found The Thing That Was Not A Bacterium · Microbiologist & Botanist · 1851–1931

The Delft microbiologist who showed that an infectious agent could pass a filter no bacterium could, and multiply only inside a living cell.

Who was Beijerinck?

Martinus Willem Beijerinck was born in Amsterdam in 1851 and trained at Delft and Leiden. He taught at an agricultural school, worked for a yeast factory, and only in 1895 was given the Delft professorship in which he did his best work. His method was the enrichment culture, and it changed microbiology: rather than trying to grow everything and pick out what he wanted, he set the conditions — the food, the gases, the salts — so that only the organism he was hunting could survive them, and let it find him. By it he isolated in 1888 the root-nodule bacterium that fixes atmospheric nitrogen for legumes, and later the free-living nitrogen fixers and the sulphate-reducing bacteria, establishing that the great chemical cycles of the soil are run by organisms. In 1898 he returned to the mosaic disease of tobacco. Adolf Mayer had shown in 1886 that the sap of a diseased plant would infect a healthy one. Dmitri Ivanovsky had passed that sap through a Chamberland porcelain filter in 1892, found the filtrate still infectious, and concluded that his filter must be faulty or that a bacterial toxin had come through. Beijerinck repeated the filtration and then did what neither had: he let the filtrate diffuse down into a plate of clear agar and recovered the infectious agent from deep inside it, where no bacterium could have travelled. He showed the agent multiplied rather than merely being diluted, since sap from a newly infected plant was as potent as the original — and that it would multiply only in living, dividing plant tissue, never in any broth on his bench. He named it a contagium vivum fluidum, a contagious living fluid, and he meant every word, including the fluid. He died at Gorssel in 1931.

Major achievements

• Showed in 1898 that the tobacco mosaic agent passes a bacteria-proof filter and diffuses through agar
• Demonstrated that the agent multiplies, and only inside living dividing tissue
• Named it contagium vivum fluidum, opening the study of what became virology
• Isolated the root-nodule bacterium that fixes nitrogen for legumes, 1888
• Discovered free-living nitrogen-fixing and sulphate-reducing bacteria

Life in brief

• 1851 — Born in Amsterdam: Into a family whose tobacco business would fail.
• 1888 — Nitrogen fixation: Isolates the root-nodule bacterium that feeds legumes from the air.
• 1895 — Professor at Delft: Given a laboratory of his own after years in schools and industry.
• 1898 — The filtrate: Shows the tobacco agent passes a bacteria-proof filter and diffuses into agar.
• 1901 — Sulphate reducers: Adds another of the soil's chemical cycles to the list microbes run.
• 1921 — Retirement: Leaves the Delft chair; the laboratory keeps his method.
• 1931 — Dies at Gorssel: Before anyone had seen the thing he found.

Explore the life of Beijerinck — five chapters

1. Twenty Years Before a Laboratory — A failed tobacco business, a yeast factory, and a difficult man
2. The Microbes That Run the Soil — Nitrogen fixation, and the cycles nobody had attributed to organisms
3. Something That Passed the Filter — Tobacco mosaic disease, 1898
4. Only Inside Something Living — The finding that defines a virus
5. Wrong About Two Words — Not a fluid, and not alive

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