A human figure is dwarfed by a fanciful mushroom, mold, and bacterial jungle.

The Magic in Mold and Dirt

Circulating Now welcomes guest bloggers Diane Wendt and Mallory Warner from the Division of Medicine and Science at the Smithsonian National Museum of American History. As curators of our most recent exhibition, From DNA to Beer: Harnessing Nature in Medicine and Industry, Diane and Mallory spent months researching four different microbes and the influence they’ve had on human life.

One of our favorite objects in the exhibition From DNA to Beer is a bag of dirt.

“The humblest spadeful of earth from your garden contains almost unbelievable medical magic.”—J.D.Ratcliff, Yellow Magic

A clear plastic bag containing a soil sample and card dated 7/31/49.
Soil sample, 1949
Courtesy National Museum of American History

This “dirt bag” (as it was affectionately dubbed by Library staff) was donated to the Smithsonian in 1953 by the pharmaceutical firm Charles Pfizer & Company and its story is delightfully told in the book Our Smallest Servants (Charles Pfizer & Co., 1955).

The tiny “servants” of the title are none other than the innumerable microorganisms that inhabit our world, specifically those that have been “harnessed” to do our bidding.  In the words of Pfizer’s then President, John E. McKeen, who introduces the book, “This book deals with one of the most momentous and far-reaching of all scientific achievements: the ability to harness microscopic living creatures in the service of mankind.”

The main delight in this book lies in its imaginative illustrations beginning with the array of Petri dishes on the cover and the cut-away circle and culture of “mold” that follows you as you page through the book.

Further on in the book we learn that the name of this mold is Penicillium chrysogenum. This particular microorganism was recovered from a moldy cantaloupe purchased at a market in Peoria, Illinois in the early 1940s.  The rotten fruit was taken to a nearby government laboratory where researchers were working around the clock to try to find ways to mass-produce penicillin.  The antibiotic, which is produced by the Penicillium mold, was first discovered in 1928 by Alexander Fleming.  However it was not yet a useful medicine because it could not be manufactured on a large scale. To give a sense of the magnitude of the problem, the author relates that in 1939 you could recover more gold from ordinary seawater than penicillin from a Penicillium culture.

The discovery of Penicillium chrysogenum, which replaced Fleming’s mold Penicillium notatum in the research work, was an important step in meeting this challenge. The new mold produced a much higher yield of penicillin, and it could thrive in enormous, deep tanks of a special nutrient broth. In the author’s words, “Feeding on a newly formulated liquid composed mainly of water in which corn had been steeped, the disciplined mold produced tons of the antibiotic in time to save thousands of Allied lives.

And so we have a wonderful story about a moldy fruit … but what about our dirt bag?

A human figure is dwarfed by a fanciful mushroom, mold, and bacterial jungle.
This fanciful illustration from the book of the lush microbial world is one of our favorites.

At the same time researchers were working on penicillin, scientists at a laboratory at Rutgers University were busy studying the properties of microorganisms isolated from the soil.  The scientists laboriously cultivated thousands of samples before they found the bacteria Streptomyces griseus, which yielded an important new antibiotic, streptomycin.  Streptomycin was effective against many bacterial infections that were resistant to penicillin including Mycobacterium tuberculosis, which causes tuberculosis.

The success of penicillin and streptomycin prompted a tremendous, world-wide search for new, useful microorganisms, and in this “global treasure hunt” American pharmaceutical laboratories led the way. Soil, naturally rich in microbial life, was a good place to search.  As our author explains:

“Any reasonably typical teaspoonful of rich, moist earth contains numerous colonies of microbial existence, with a combined population of as many as three hundred million organisms. Under the microscope, a pinch of such soil springs to life and stands revealed as a lush, spectacularly beautiful and unremittingly violent jungle, in which strange beings wage endless war for food, water, living space, and survival.”

A sample bag of dirt is laid on top of a world map.
The bag of dirt!

The Pfizer Company alone screened over 100,000 soil samples, before it hit pay dirt:

In 1949, a bit of earth which had been spooned up near one of Pfizer’s own Middle Western plants was found to contain an actinomycete worthy of extensive investigation.  The creature was named Streptomyces rimosus, and the canary yellow crystals of its antibiotic were called Terramycin.”

And finally we find our dirt bag—one of the many soil samples collected and screened by the Pfizer Company. Ironically, although they collected soil from all over the world – as alluded to in this illustration from the book – the winning dirt was found almost literally in their backyard.  The bag of dirt donated to the Smithsonian and now on display at the National Library of Medicine contains some of this sample. Terramycin proved to be effective against a wide range of diseases—nearly one hundred—including typhus and Rocky Mountain fever.

We last meet our mold among a field of cattle, as our story relates how antibiotics such as Terramycin were found to be effective growth promoters.  When animal feed is enriched with antibiotics, livestock such as poultry and swine “reach market size sooner, and on less feed.”  More meat for the money is one way to look at it.

We don’t know the end of the antibiotic story, but we do know that it has become increasingly complicated over the years since the publication of Our Smallest Servants.  Already by the mid 1950’s concern arose over penicillin residue in milk, and the Asian flu pandemic of 1957-58 introduced the public to the emergence of antibiotic resistant microorganisms.  Responsible antibiotic use has been a subject of debate ever since, and recently the FDA has issued new guidelines concerning their use in animal feed. Our relationship with “our smallest servants” continues to evolve.

Explore From DNA to Beer: Harnessing Nature in Medicine & Industry online for yourself at http://www.nlm.nih.gov/exhibition/fromdnatobeer/index.html. To book the traveling exhibition or see when it comes to your town, visit the traveling exhibition page at http://www.nlm.nih.gov/hmd/about/exhibition/fromdnatobeer-bookinfo.html. Read more posts in this series here.


  1. I found your report on the discovery of antibiotics so interesting! I know that the use of antibiotics by doctors has been indiscriminate for many years, even when not really necessary to help their patients’ symptoms. I suspect that it is the reason for the new mutant strains of the bacteria and viruses. 🙂

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