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

Abstract

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 multitaxa 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. Here we explore the mechanisms behind the protection effect against the native pathosystem. Three members of the consortium, Pseudomonas azotoformans A70, P. frederiksbergensis A176 and Arthrobacter nitroguajacolicus E46, form biofilms when grown individually in vitro, and the amount of biofilm increased synergistically in the five‐membered consortium, including two Bacillus species, B. megaterium and B. mojavensis. Fluorescence in situ hybridization and 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.

Screening of the High-Rhizosphere Competent Limoniastrum monopetalum’ Culturable Endophyte Microbiota Allows the Recovery of Multifaceted and Versatile Biocontrol Agents

“…The basis for the observed activity of Bacillus spp. against Fusarium pathogenic species has been linked to secondary metabolites that strongly interfere with fungal pathogens [74,75]. To test the validity of our strategy against emerging pathogens, we isolated Fusarium sp.…”

Microbial Interactions Within Multiple-Strain Biological Control Agents Impact Soil-Borne Plant Disease

“…Several microbial combinations are possible, such as fungus to fungus, fungus to bacterium, and bacterium to bacterium. Similar to the single-strain biological control agents (SSBCAs), MSBCAs employ diverse modes of action for control, e.g., competition for resources and niches ( McKellar and Nelson, 2003 ; Wei et al, 2015 ; Hu et al, 2016 ), production of antimicrobial compounds ( Thakkar and Saraf, 2014 ; Santhanam et al, 2019 ), induction of systemic resistance ( Sarma et al, 2015 ; Solanki et al, 2019 ), and regulation of microbial communities ( Zhang L.-N. et al, 2019 ). MSBCAs appear to have higher efficiency for control of soil-borne disease than SSBCAs ( Figure 1A ).…”

“…Inoculation with MSBCAs may enhance the colonization of the rhizosphere by biocontrol microbes. The rhizoplane colonization ability of a five-strain bacterial consortium suppressing a sudden wilt disease of Nicotiana attenuata was enhanced compared to that of each single community member ( Santhanam et al, 2019 ). Survival of Pseudomonas species communities inhibiting bacterial wilt disease of tomato increased with increasing diversity ( Hu et al, 2016 ).…”

“…In a previous study, a consortium of five native bacterial isolates was found to be able to colonize the roots of N. attenuata by forming multiple-taxa biofilms on the root surfaces. Furthermore, under both in vitro and in vivo conditions, the amount of biofilm produced by each individual strain was significantly less than the biofilms formed by the five-membered bacterial community, which indicating a synergistic biofilm formation by the consortium ( Santhanam et al, 2019 ). Similarly, a three-species biocontrol community composed of Xanthomonas sp.…”

“…Moreover, colonization of host roots by this community was stimulated by enhanced biofilm formation ( Berendsen et al, 2018 ). Although the mechanisms of such positive effects on biofilm production are unclear, the improved efficacy can be attributed to the cooperative microbial interactions in consortia, triggering increased extracellular matrix deposition and cell-to-cell signaling ( Santhanam et al, 2019 ).…”