A seed-endophytic bacterium NEAU-242-2: Isolation, identification, and potential as a biocontrol agent against Bipolaris sorokiniana

Abstract

Currently, common root rot of wheat has caused significant yield losses worldwide. Biological control is an important method to control common root rot of wheat. An endophytic bacterium, strain NEAU-242-2 was isolated from wheat seeds, which showed the strongest inhibitory activity against Bipolaris sorokiniana (84.2%) and also had strong broad-spectrum antifungal activity, with the inhibition rates over 61.2% against all phytopathogens used in this study except for Rhizoctonia solani (44.5%), and was identified as Bacillus velezensis by 16S rRNA gene sequence and whole genome sequence and average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values. Pot experiments showed that strain NEAU-242-2 exhibited significant biocontrol effect (80.61 ± 1.22%) on common root rot of wheat in greenhouse. Furthermore, the sterile culture filtrate of strain NEAU-242-2 had strong inhibitory activity (86.96 ± 3.02%) against B. sorokiniana and the main antifungal substance was preliminarily identified as lipopeptides. The crude lipopeptide extracted from strain NEAU-242-2 showed strong antifungal activity (61.45 ± 3.45%) against B. sorokiniana with the IC50 of 25.93 µg/mL, and could cause mycelial wrinkle, fracture, and dehydrated malformation, destroy the structure of cell, and lead to cellular malformation and the disappearance of most membrane-like structures. Besides that, strain NEAU-242-2 could also conspicuously promote wheat seed germination and seedling growth. The fungistasis and plant growth-promoting activity of strain NEAU-242-2 were found to be associated with the production of IAA (19.4 ± 0.6 µg/mL), siderophores, nitrogenases, cell wall-degrading enzymes (proteases and cellulases), and other active secondary metabolites. Additionally, a large number of genes related to antifungal and plant growth-promoting traits were also identified in the whole genome of strain NEAU-242-2. These results indicated that strain NEAU-242-2 had the potential as a biocontrol agent for B. sorokiniana.