Soil-inhabiting fungal pathogens use chemical signals released by roots to direct hyphal growth towards the host plant. Whether other soil microorganisms exploit this capacity for their own benefit is currently unknown. Here we show that the endophytic rhizobacterium Rahnella aquatilis locates hyphae of the root-infecting fungal pathogen Fusarium oxysporum through pH-mediated chemotaxis and uses them as highways to efficiently access and colonize plant roots. Secretion of gluconic acid (GlcA) by R. aquatilis in the rhizosphere leads to acidification and counteracts F. oxysporum-induced alkalinisation, a known virulence mechanism, thereby preventing fungal infection. Genetic abrogation or biochemical inhibition of GlcA-mediated acidification abolished biocontrol activity of R. aquatilis and restored fungal infection. These findings reveal a new way by which bacterial endophytes hijack hyphae of a fungal pathogen in the soil to gain preferential access to plant roots, thereby protecting the host from infection.

居住在土壤中的真菌病原体利用根部释放的化学信号将菌丝定向到宿主植物上。目前尚不清楚其他土壤微生物是否为自己的利益而利用这种能力。在这里，我们显示了内生水生根瘤菌Rahnella aquatilis通过pH介导的趋化作用定位了根部感染真菌病原菌尖孢镰刀菌的菌丝，并将其用作有效进入和定植植物根的高速公路。葡糖酸的分泌（中，GlcA）由R. aquatilis在根际导致酸化并抵消尖孢镰孢-诱导的碱化，一种已知的毒力机制，从而防止真菌感染。遗传废除或中，GlcA介导的酸化的生化抑制废除的生物防治活性R. aquatilis和恢复真菌感染。这些发现揭示了细菌内生菌劫持土壤中真菌病原体菌丝以获得植物根系优先进入途径的新途径，从而保护宿主免受感染。