Rhizosphere beneficial microbes are the main source of strains in microbial fertilizers, and efficient rhizosphere colonization is the prerequisite for exerting various beneficial functions to plant. The colonization of microbes in the rhizosphere includes three main processes: chemotaxis towards rhizosphere, root adhesion, and biofilm formation on root surface, and each step is driven by signal-mediated bacteria-plant interactions. Available iron is a limited resource in the rhizosphere environment, and both bacteria and plants have their specific strategy to obtain it. Rhizosphere microbes need iron to form a biofilm on the root surface, and they mainly compete for it in the rhizosphere soil by secreting siderophores.

Once the rhizosphere microbe has colonized the root surface and formed a biofilm, they can continuously improve plant iron nutrition by the siderophores and biofilm matrix. Therefore, it is beneficial for plants to quickly start the colonization and biofilm formation of the beneficial microbes on the root surface of plants. Is there a mechanism that promote the rapid colonization of beneficial microbes in the rhizosphere during the long-term co-evolution of beneficial microbes and plants?

Recently, Nature Microbiology (IF=30.964), published the article paper of the agricultural microbial resource team online (Plant commensal type VII secretion system causes iron leakage from roots to promote colonization).

This study used the widely used microbial fertilizer strain Bacillus velezensis SQR9 as the research material, and found that the YukE secreted by its type VII secretion system can insert into the root cell membrane in the early stage of plant-bacteria interaction, causing transient iron leakage in the root cells. As the iron concentration in plant root cells is higher than in the soil, the root iron leakage provide iron for Bacillus to quickly colonize the root surface. The experiment proved that this interaction promoted the growth-promoting effect of Bacillus. It proposes a novel interaction mode between rhizosphere microbes and plants, and provides theoretical guidance for the efficient functioning of the beneficial microbes in microbial fertilizers.

Nature Reviews Microbiology, the top review journal in the field of microbiology, devoted a whole page to this article in the form of "Research Highlights" under the title "Bacterial secretion-An intended leak".

The associated professor Liu Yunpeng, and Ph.D student Shu Xia at the Agricultural Microbial Resources of the Institute of Agricultural Resources and Regional Planning (IARRP) of the Chinese Academy of Agricultural Sciences (CAAS), and associated professor Chen Lin at the Experimental Center of Forestry in North China, Chinese Academy of Forestry, are the co-first authors of the paper. Professor Zhang Ruifu and associated professor Liu Yunpeng are the co-corresponding authors of the paper.

This work was funded by the National Natural Science Foundation of China, the Central Public-interest Scientific Institution Basal Research Fund and the Agricultural Science and Technology Innovation Program.

Paper link: https://www.nature.com/articles/s41564-023-01402-1