Rare bacteria key to fighting dangerous fungus

Pretty but dangerous: that's the Fusarium-fungus gracing the cover of the August issue of Ecology. Bacteria can stop the fungus from infecting plants. But it's a surprisingly delicate balance, discovered a team of NIOO-researchers.

Soil bacteria may be invisible to the human eye, but that doesn't mean you won't notice them. Just think of the way the woods smell after a summer shower.

That smell is caused by volatiles produced by bacteria as a way of communicating with each other across distances. But they also use these volatiles to control rival organisms in the soil. Organism such as fungi.

Bacteria that stop or stunt the growth of fungi are found in almost all soils. They form a natural defense mechanism against soil-borne pathogens, a present from mother nature that farmers and horticulturists should be very grateful for.

Reducing biodiversity

The number of different species of bacteria in the soil can be staggering. Considering how widespread a phenomenon the suppression of diseases by bacteria is, and in how many different types of soil, one may well wonder if they're all really needed. Aren't most of those species just passive bystanders while a small number of dominant ones drive the process?

But what would happen if the rich species diversity was suddenly to be reduced? What if researchers were to take bacterial communities from different types of soil and dilute them step by step, until the rarer species had all disappeared from the mix?

Surprising results

That's precisely what Gera Hol and her team of NIOO-researchers did. And the results they have just published in the August issue of Ecology are surprising.

Even after just a single dilution, some of the more important volatiles that suppress Fusarium oxysporum were no longer being produced. And the more of the rarer species of bacteria were filtered out through repeated dilutions, the less inhibited the growth of the Fusarium-fungus would be.

Year of Soils

The results suggest that even the least abundant members of the bacterial community still play a key role in producing vital volatiles, either directly or perhaps by 'activating' some of the other, more dominant species. It's something farmers and horticulturists should start taking into account, believes Gera Hol.

"For agriculture and horticulture, soil-borne pathogens are a source of continuous concern. But if you disinfect the soil, you also disrupt the production of these volatiles." Repairing the damage takes up to a year, other research concluded after looking at the way bacteria protect hyacinth bulb tissue.

At any rate, this International Year of Soils seems to be a perfect time to reasses the role of organisms that too often tend to be - literally - overlooked.
 

• 'Non-random species loss in bacterial communities reduces antifungal volatile production', W. H. Gera Hol, Paolina Garbeva, Cornelis Hordijk, Maria P. J. Hundscheid, Paulien J. A. Klein Gunnewiek, Maaike van Agtmaal, Eiko E. Kuramae, Wietse de Boer, Ecology Vol. 96, Issue 8 (August 2015)