A novel bacterial species named after a Finnish Nobelist A.I. Virtanen

Artturi Ilmari Virtanen is best known for his work on fodder preservation method, which earned him a Nobel Prize award in Chemistry in 1945. What is rarely mentioned in his biographies, is his pioneering research on Propionic Acid Bacteria (PAB).

PAB, named collectively for their production of propionic acid as the main end product of fermentation, include several species of important bacteria: from the vitamin B12-producer and emerging probiotic Propionibacterium freudenreichii, through industrial producer of propionic acid Acidipropionibacterium acidipropionici, to opportunistic human pathogen Cutibacterium acnes.

The first reports of PAB being isolated and described came at the very beginning of the 20th century. In the early 1920s, Virtanen also worked on characterisation of strains he isolated from the brown spots of Finnish Emmental-type cheeses. However, it was not until 1928 that a breakthrough in PAB research came with the doctoral thesis of Cornelius Bernardus van Niel from the Delft University of Technology, where systematic classification and species naming took place.

To honour the researchers who either first isolated or contributed to the understanding of the biology of PAB, van Niel named the species after their discoverers, among them Eduard von Freudenreich (freudenreichii), Sigurd Orla-Jensen (jensenii), Gerda Troili Petersson (peterssonii), James M. Sherman (shermanii) and J. Thön (thoenii). However, Virtanen missed out on a species name, as Virtanen himself believed that his strains belonged to already described and named Acidipropionibacterium thoenii.

In the University of Helsinki, during sequencing project of PAB isolated from various environments, researchers worked with a PAB strain isolated from Finnish malted barley, which displayed similar pigmentation and branching cell shape to those described by Virtanen. As it turned out the, the strain was sufficiently genetically different from A. thoenii and its known relatives to form a novel species.

"While we have no way of knowing whether the novel species isolated in Finland could be in fact the species Virtanen described in his work, we still decided to name the novel species Acidipropionibacterium virtanenii in his honour and to ensure Virtanen's name is recognised among those who contributed to the pioneering PAB research," says Paulina Deptula, Postdoctoral Researcher in the Faculty of Agriculture and Forestry.

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