by Mathias Grote
There is more to say about these two articles of glassware other that every microbiologist knows than that both were invented almost exactly 130 years ago by their respective eponyms, the German Julius Richard Petri and the Russian-French Sergei N. Winogradsky. What is interesting about these devices is that they embody two different, even contrary approaches to study the microbial world – one, Petri's, based on pure cultures, synthetic media and medicine, the other, Winogradsky's inspired by natural environment and ecology.
These approaches have been juxtaposed throughout microbiology's history, until recently when Winogradsky's column, in modern words a miniature ecosystem containing mixes of aquatic microbes, became a display for how to think of microbes: Amsterdam's microbe museum Micropia (featured here in STC), for example, presents to visitors a giant Winogradsky column in an attempt to explain metabolic types and interactions of microbes, as well as their influence on ecosystems, whereas the American Museum of Natural History used them as a model of the human gut microbiome. The Petri dish has been a mainstay for how to conceive of microbes for almost a hundred years, but it now seems that the main premises of this technique – pure cultures representing clearly delineated microbial species in isolation, are being questioned. "The great culture plate anomaly" has suggested for a while that there are many more microbes out there than can be cultured under standard conditions, and genomic technologies have undermined clear species concepts as are used for macrobes. It looks like the microbial world out there is much more Winogradskian (dirty, mixed) than Petrian (clean, pure). What can these shifting ways of thinking of microbial species and diversity tell us about the historical development of microbiology?
But first, here's how these devices came into use more than a century ago: Double glass dishes fitting loosely into one another were introduced somewhat modestly by its eponym, Julius Richard Petri, under the title "A small modification of Koch's plate technique". No longer than a page, Petri's article belongs to bacteriology's heroic age: A few years before, Robert Koch, who had just demonstrated anthrax infection, introduced solid media for culturing bacteria. Among these were gelatin and agar-agar (reportedly on the advice of one of his staff member's wife, who knew the substance as a jellying agent for food preparation; Collard 1976). Koch devised solid culture plates by pouring broth mixed with a jellying agent on a glass surface. Koch's almost ludicrously simple innovation allowed him to make a powerful argument in a controversy raging in late 19th century bacteriology between the so-called monomorphists (himself and his former mentor, Ferdinand Julius Cohn), who assumed that stable bacterial species existed. The opposing pleomorphists, by contrast, argued that the microbial realm manifested a continuity of life forms, which changed in cell shape and physiological effects through life cycles and in reaction environmental conditions.
Once a microbial sample, isolated, for example, from an infected animal, was growing immobilized on the surface of Koch's plates, "Reinkulturen" (pure cultures) could be obtained as colonies on the agar. So, the Petri dish became a basic tool for this splitting of microbial diversity.
However, early users of Koch's plate method had faced technical problems when pouring the agar on glass plates, especially with contamination by air-borne germs. Enter Petri: The later director of a tuberculosis sanatorium (described by one of his staff members as a "stalwart, priggish Prussian schoolmaster") suggested to pour the inoculated liquid gelatin directly into a small, sterilized glass dish: "If this is done by lifting the top dish only slightly and pouring out the gelatin-containing test tube under its cover, one has to face contamination by air-borne germs only extremely rarely." (Petri 1887: 279. On Petri, Plesch 1951: 40 f.). Petri's dish rapidly became a staple of the bacteriological laboratory as they facilitated the adoption of Koch's plate method. The dishes were much more easily handled in the lab for their small size, they could be stacked upside down in an incubator (which also prevented water condensation on the plate), and cultures were easily inspected through the flat lid (see Collard 1976). For years and decades, the Petri dish and a number of related technologies turned into the central means to study microbes in the lab, and pure cultures were the sine qua non of taxonomy. To validly describe a microbe in taxonomic papers, pure cultures were required.
Yet, the main premises of the Petri dish and pure culture have never been uncontested: Since the early 20th century, Sergei N. Winogradsky had been a vocal critic of the approach which he thought would artificially distort microbial types due to the synthetic plate media (such as broth) and the unnatural mass growth thereon. He analogized this situation with plants being incubated for years in a green house. Microbial ecologists actually came forward with other methods to study microbial diversity, such as enrichment cultures. And this is where the Winogradsky column comes in: Without using that name (which is probably a term from the second half of the 20th century, see here), he described in a contribution from 1888 on the isolation of Beggiatoa from pond waters via a device that comes close to what we now know as 'the' column: A long jar filled with mud and pond water, to which gypsum was added (as a source of sulphur), was incubated for weeks in order to make aquatic microbes such as Beggiatoa grow in the lab. It is easily seen how this device embodies a completely different approach to microbiology: It was unsterile, and it mimicked the natural environment by growing mixed populations in situations that come close to the habitat in many respects.
Winogradsky's ecological approach has always been present in the 20th century, being used not only as a culturing device, but after 1970, increasingly as a display for ecological processes, such as the circulation of metabolites between different microbial communities. However, this way of thinking of microbes has remained marginal for decades, as an ecological approach was overshadowed by the power and dominance of pure culturing, especially when it came to infections or taxonomy.
As mentioned, the tide is turning, and many microbiologists accept more of the premises connected with Winogradsky's ecological approach. Why this is so, is an interesting historical question – technological factors such as the surge of DNA sequencing, and thereby the decreasing relevance of culturing methods, certainly play a role, possibly also a general rise of ecological thinking – this is discussed in more detail in the paper. What seems clear from a historical standpoint is that microbiology is currently revising the approach for how to study microbes, as well as the concepts of what microbes are and how to study them properly.
And here's a speculation, turning from history to prognosis for the 21st century: Winogradsky will probably not become a staple name of the lab as Petri’s (today, microfluidic devices can be used for ecologically-minded culturing). However, with the rise of culture-independent genomic methods, should the Russian ecologist’s name not be enshrined in the history of microbiology and its public perception, similar to Pasteur and Koch? And in the end, might Petri's dish and pure culture not be considered as a very specific style of doing microbiology in the bygone 20th century, now only one among many ways of dealing with microbial diversity?
Collard P. 1976. The development of microbiology. Cambridge University Press, Cambridge UK
Grote M. 2018. Petri dish versus Winogradsky column: a longue durée perspective on purity and diversity in microbiology, 1880s–1980s. Topical Collection "New Perspectives in the History of the Life Sciences", ed. R. Meunier and K. Nickelsen, History and Philosophy of the Life Sciences 40, 11.
Grote M. (forthcoming). Petri dish. In: Bauer S, Schlünder M, Rentetzi M, eds., Boxes in Action. Mattering Press, Manchester UK
Koch R. 1912. Zur Untersuchung von pathogene Mikroorganismen . In: Schwalbe J, ed., Gesammelte Werke von Robert Koch, Vol.1, 112 – 163. Verlag von Georg Thieme, Leipzig D
Petri JR. 1887. Eine kleine Modification des Koch'schen Plattenverfahrens. Centralblatt für Bacteriologie und Parasitenkunde, 1, 279 – 280
Plesch J. 1951. Ein Arzt erzählt sein Leben. Paul List Verlag, München D
Mathias Grote is a microbiologist turned historian of science working at Humboldt-University of Berlin. He has published on the history of the 20th century life sciences (with a special focus on membranes, which kept him busy in the lab during his PhD). In his current project, he pursues the question of what happens to knowledge once it becomes “old”, especially in taxonomy and classification of microbes.