Multi-omics analysis of Bacillus-associated suppression of Bursaphelenchus xylophilus disease symptoms and candidate defense responses in Pinus thunbergii

Abstract

Pine wilt disease (PWD), caused by Bursaphelenchus xylophilus , is a devastating threat to pine forests worldwide. This study evaluated the biocontrol potential of two Bacillus strains, Bacillus thuringiensis B122 and Bacillus velezensis B223, isolated from post-logging rhizosphere soil, to suppress PWD symptoms and characterize associated host responses in Pinus thunbergii. Root drenching with bacterial suspensions was applied, followed by nematode inoculation. Disease severity and relative control efficacy were assessed. Early needle assays measured hydrogen peroxide, malondialdehyde, peroxidase, and superoxide dismutase responses. Integrated transcriptomic and metabolomic analyses were used to identify candidate molecular associations underlying differential efficacy. Root drenching with bacterial suspensions significantly reduced disease severity after nematode inoculation. B223 exhibited superior relative control efficacy (76.1%) compared with B122 (40.8%). Early needle assays revealed strain-associated differences in hydrogen peroxide, malondialdehyde, peroxidase, and superoxide dismutase responses. Integrated transcriptomic and metabolomic analyses identified candidate molecular associations underlying this differential efficacy. Both strains were associated with enrichment of defense-related pathways, including MAPK signaling, phenylpropanoid biosynthesis, and flavonoid biosynthesis. B223 showed distinct enrichment of the plant hormone signal transduction pathway, including jasmonate/ethylene (JA/ET)-related annotations, and broader metabolic reprogramming. We propose a cautious working model in which B223-associated symptom suppression may involve coordinated hormone-related transcriptional responses, MAPK signaling, and downstream phenylpropanoid/flavonoid metabolism. Collectively, these data support B223 as a promising biocontrol candidate against PWD.