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Digging for Medicine: Rene Dubos, Soil Bacteria and the First Peptide Antibiotic
Before penicillin was a household word, a microbiologist at the Rockefeller Institute in New York was literally digging through dirt to find something that could kill bacteria. What René Dubos found in 1939 was a peptide antibiotic, and it started the whole modern search for medicines from soil.
Key takeaways
- Dubos wanted a microbe that could break down the protective capsule of pneumococcus, and widened his search to soil bacteria that killed other bacteria.
- In 1939 he isolated tyrothricin from Bacillus brevis, a mixture of two peptide families: gramicidin and tyrocidine.
- Gramicidin is a short peptide with alternating mirror-image amino acids.
- It was too toxic to inject but became the first commercially produced antibiotic, used on skin and wounds.
- It inspired Selman Waksman’s search that found streptomycin, and its analysis helped win the 1952 Nobel Prize in Chemistry.
A search through the soil
Dubos was inspired by the idea that soil is full of microbes that compete with each other, and that the losers might be killed by chemical weapons made by the winners. He enriched soil samples with disease-causing bacteria, then watched which soil microbes survived and what they produced.
In 1939 he isolated a bacterium, Bacillus brevis, whose extract killed many Gram-positive bacteria in a dish and protected animals from infection.
Tyrothricin and its peptides
The extract, named tyrothricin, was a mixture. Its two main components were gramicidin and tyrocidine, both peptides. Gramicidin is made of a short chain that alternates between ordinary L-amino acids and unusual D-amino acids, a pattern that lets it form a tube-like helix in membranes. That tube lets ions flow through, which kills bacterial cells.
The unusual D-amino acids also make it resistant to common proteases. We discuss why that works in half-life engineering and chiral purity.
Too toxic to inject
Tyrothricin was powerful but damaged red blood cells when injected, so it could only be used on the skin and in wounds. Even so, it was the first antibiotic produced commercially, and it proved that a drug could come from a soil microbe. That was a crucial step for the search that followed. Selman Waksman at Rutgers launched a systematic screening program that led to streptomycin, and by the 1940s penicillin joined the list.
A gift to chemistry
In the early 1940s, Archer Martin and Richard Synge developed partition chromatography, a way to separate and measure the amino acids in a protein or peptide using paper and solvents. Synge went on to use the method to work out the composition of gramicidin S, a related Russian peptide. They received the 1952 Nobel Prize in Chemistry. Their technique paved the way for the sequencing methods used by Frederick Sanger.
Why antimicrobial peptides still matter
Gramicidin is still used topically today, and the broader idea that organisms make peptides to defend themselves led to the discovery of many more, including those described in the magainin story. Studying how peptides interact with bacterial membranes is a lively field, and the experimental tools described in the USP 51 test guide and wound models are part of it.
The bottom line
The gramicidin story shows how a single idea, that soil is a pharmacy, can change a field. It was a peptide that started it. Browse more stories in the Research Library.
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For laboratory research use only. Not for human or veterinary use, and not intended to diagnose, treat, cure or prevent any condition. This article is educational and is not medical advice.