The recruitment of Streptomyces bacteria to the plant root microbiome

Species in this genus are abundant in soil but are also enriched in and around the roots of many different plant species, including cereal crops and the model plant Arabidopsis thaliana. Here, they can promote plant growth and protect against disease. However, little is known about the factors that attract Streptomyces to plant roots and allow them to establish there.

Sarah Worsley, with colleagues from the University of East Anglia, the John Innes Centre and the Open University, investigated whether Streptomyces and other soil bacteria were attracted to carbon released from A. thaliana roots (root exudates). Using in vitro assays and plant colonisation experiments their research demonstrated that, despite previous reports, Streptomyces species were not attracted to, and couldn’t grow, using the plant defence phytohormone, salicylic acid. Furthermore, ¹³CO₂ stable isotope probing combined with amplicon sequencing revealed that Streptomyces weren’t feeding on other root exudates in the A. thaliana root microbiome- these were instead metabolised by faster-growing proteobacteria like Pseudomonas species. Under these conditions, Streptomyces are likely to be feeding off more complex organic material shed by the plant roots as they grow. This research highlights the variety of mechanisms by which bacteria are maintained within the plant root microbiome. Such information will be important if we are to improve the competitiveness and efficacy of biocontrol strains that are introduced to protect plants against disease. To read more about this research please see:  https://doi.org/10.3389/fmolb.2021.686110