Microbial Lingua Franca Links Bacteria and Fungi, Modifies Gene Expression

The soil fungus Fusarium shares a good conversation with unrelated soil bacteria. [Heike Engel/21Lux photography]

Intimately mingled soil microbes are a cosmopolitan lot. They even share a sort of lingua franca, one that allows them to send and receive chemical signals across phylogenetic domains. For example, bacteria and fungi both speak in terpenes, which can, researchers have shown, induce responses at the transcriptomic, proteomic, and metabolomic levels.

New details about this shared microbial language appeared April 13 in the journal Scientific Reports, which published a paper (“Fungal Volatile Compounds Induce Production of the Secondary Metabolite Sodorifen in Serratia plymuthica PRI-2C”) prepared by scientists based at the Netherlands Institute of Ecology.

The researchers have demonstrated that bacteria and fungi respond to each other’s chemical signals. In other words: they can hold conversations.

“Serratia, a soil bacterium, can 'smell' the fragrant terpenes produced by Fusarium, a plant pathogenic fungus. It responds by becoming motile and producing a terpene of its own,” explained Paolina Garbeva, Ph.D., a microbiologist at the Netherlands Institute of Ecology.

Her team studied which genes were switched on by the bacterium, which proteins it began to produce, and which fragrance. “Such fragrances—or volatile organic compounds (VOCs)—are not just some waste product,” Dr. Garbeva insisted. “They are instruments targeted specifically at long-distance communication between these minute fungi and bacteria.”

But how widespread is this language of smells? Pathogenic soil fungi such as Fusarium also have an effect above ground, where they make plants sick. Can they communicate with those plants?

“We find that the bacterium responds to fungal VOCs with changes in gene and protein expression related to motility, signal transduction, energy metabolism, cell envelope biogenesis, and secondary metabolite production,” the Science Reports article detailed. “Metabolomic analysis of the bacterium exposed to the fungal VOCs, gene cluster comparison, and heterologous co-expression of a terpene synthase and a methyltransferase revealed the production of the unusual terpene sodorifen in response to fungal VOCs.”

“We have known for some time that plants and insects use terpenes to communicate with each other,” noted Dr. Garbeva. “But we've only just begun to realize that it's actually much wider. There is a much larger group of 'terpene-speakers'—micro-organisms.”

Terpenes act as pheromones—chemical signals used by animals—which makes them a regular ingredient of perfumes. So, it's likely that the language of terpenes forms a vast chemical communications network indeed.

Terpenes are by no means the only VOCs that are in for a good chat. The researchers found others as well: in the soil, for instance. Dr. Garbeva's Ph.D. student Ruth Schmidt, the first author of the article, added: “Organisms are multilingual, but 'terpene' is the one that's used most often.”

Who knows, maybe without realizing it we are native speakers too?