A suite of complementary biocontrol traits allows a native consortium of root-associated bacteria to protect their host plant from a fungal sudden-wilt disease.
The beneficial effects of plant-bacterial interactions in controlling plant pests have been extensively studied with single bacterial isolates. However, in nature, bacteria interact with plants in multi-taxa consortia, systems which remain poorly understood. Previously, we demonstrated that a consortium of five native bacterial isolates protected their host plant Nicotiana attenuata from a sudden wilt disease (Santhanam et al., 2015b). Here we explore the mechanisms behind the protection effect against the native pathosystem. Three members of the consortium, A70 Pseudomonas azotoformans, A176 P. frederiksbergensis, E46 Arthrobacter nitroguajacolicus form biofilms when grown individually in vitro, and the amount of biofilm increased synergistically in the 5-membered consortium, including two Bacillus species, B. megaterium and B. mojavensis. FISH (fluorescence in-situ hybridization) and SEM (scanning electron microscopy) in planta imaging techniques confirmed biofilm formation and revealed locally distinct distributions of the five bacterial strains colonizing different areas on the plant-root surface. One of the five isolates, K1 B. mojavensis produces the antifungal compound, surfactin, under in vitro and in vivo conditions, clearly inhibiting fungal growth. Furthermore, isolates A70 and A176 produce siderophores under in vitro conditions. Based on these results we infer that the consortium of five bacterial isolates protects its host against fungal phytopathogens via complementary traits. The study should encourage researchers to create synthetic communities from native strains of different genera to improve bioprotection against wilting diseases. This article is protected by copyright. All rights reserved.