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Battle of the bacteria: Competition for iron can dictate the severity of plant disease outbreaks

Posted on 11 May 2020

The competition for iron between different bacteria can impact on the severity of bacterial wilt disease in crops, a new study from the University of York shows.

Healthy (back) and diseased (front) tomato seedlings infected by Ralstonia solanacearum pathogen. Credit: Ville Friman

To scavenge the iron from the environment, bacteria have evolved to secrete molecules called siderophores, which bind and transport iron into their cells using specific receptors located on their surfaces. 

This lock-key mechanism ensures that siderophores are received by the bacteria that produce them. However, the iron-loaded siderophores can also be ‘stolen’ by other members of bacterial communities leading to conflicts and competition.

The international research team from China, the UK, the Netherlands and Switzerland investigated whether siderophores from natural rhizosphere bacteria can suppress the growth of the plant pathogenic Ralstonia solanacearum bacterium in soil microbiomes and in the rhizosphere during tomato plant infections.

Bacterial wilt disease caused by R. solanacearum bacterium affects several plants including tomatoes, potatoes and banana. There is currently no efficient method of control and as a result the disease causes major economic losses.

The researchers examined the interactions between thousands of individual bacteria in 80 rhizosphere microbiomes, to show that siderophore-mediated competition for iron is a general mechanism predicting bacterial co-existence patterns in the soil and determining the severity of bacterial wilt disease incidence.

Healthy (back) and diseased (front) tomato seedlings infected by Ralstonia solanacearum pathogen. Credit: Lauri Mikonranta

Dr Ville Friman from the Department of Biology said: “We found that infections became more severe when the pathogen was able to steal the siderophores produced by the other bacteria. In contrast, when R. solanacearum was not able to use the siderophores produced by others, it became iron-starved and could not infect plants.”

“The novelty of the study is that it combines general microbiome analysis with in vitro and in planta experimental approaches to establish causalities between the composition of soil microbiomes, their key functional traits and plant health. Crucially, because most soil bacteria produce and are dependent on siderophores, it offers a universal mechanism to control bacterial interactions at the community level.

“While more work is needed to better understand lock-key mechanisms at the molecular level, iron competition could provide a general framework to engineer healthier plant-beneficial microbiomes. For example, if microbiomes can be ‘triggered’ to produce siderophores that pathogens cannot use, competition for iron could eradicate the pathogen by favouring the non-pathogenic members of the bacterial community.”

The paper, “Competition for iron drives phytopathogen control by natural rhizosphere microbiomes” is published in Nature Microbiology