Serobactins‐mediated iron acquisition systems optimize competitive fitness of H erbaspirillum seropedicae inside rice plants

H erbaspirillum seropedicae Z 67 is a diazotrophic endophyte able to colonize the interior of many economically relevant crops such as rice, wheat, corn and sorghum. Under iron‐deficient conditions, this organism secretes serobactins, a suite of lipopetide siderophores. The role of siderophores in the interaction between endophytes and their plant hosts are not well understood. In this work, we aimed to determine the importance of serobactins‐mediated iron acquisition systems in the interaction of H . seropedicae with rice plants. First we provide evidence, by using a combination of genome analysis, proteomic and genetic studies, that the H sero_2345 gene encodes a TonB ‐dependent receptor involved in iron–serobactin complex internalization when iron bioavailability is low. Our results show that survival of the H sero_2345 mutant inside rice plants was not significantly different from that of the wild‐type strain. However, when plants were co‐inoculated at equal ratios with the wild‐type strain and with a double mutant defective in serobactins synthesis and internalization, recovery of mutant was significantly impaired after 8 days post‐inoculation. These results demonstrate that serobactins‐mediated iron acquisition contributes to competitive fitness of H . seropedicae inside host plants.