Termite Nest Associated Bacillus siamensis YC-9 Mediated Biocontrol of Fusarium oxysporum f. sp. cucumerinum

• Published in: Frontiers in microbiology Vol. 13; p. 893393
• Main Authors: Zhou, Lingfeng, Wang, Junyong, Wu, Fei, Yin, Caiping, Kim, Ki Hyun, Zhang, Yinglao
• Format: Journal Article
• Language: English
• Published: Frontiers Media S.A 01.06.2022
• Subjects: antifungal activity; Bacillus siamensis; biocontrol; C15-surfactin; Fusarium oxysporum f. sp. cucumerinum; Microbiology
• ISSN: 1664-302X; 1664-302X
• DOI: 10.3389/fmicb.2022.893393

The antagonistic potential of bacteria obtained from the nest of Odontotermes formosanus was assessed against Fusarium oxysporum f. sp. cucumerinum (FOC). Of 30, seven termite nest-associated bacteria strains had biocontrol potential. Among them, the strain YC-9 showed the strongest antifungal activity toward FOC. Phylogenetic analysis of the 16S rRNA amplified product of YC-9 revealed its identification as Bacillus siamensis . The in vivo antifungal activity experiment showed that the application of YC-9 at 10 8 cfu/ml significantly reduced the cucumber wilt incidence with a control efficacy of 73.2%. Furthermore, plant growth parameters such as fresh weight, dry weight, plant height, and root height were significantly improved by 42.6, 53.0, 20.8, and 19.3%, respectively. We found that inoculation with B. siamensis YC-9 significantly increased the activity of defensive enzymes such as peroxidase (POD), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) in diseased cucumber roots, thereby raising the resistance. PCR using gene-specific primers revealed that B. siamensis YC-9 contains biosynthetic genes for known antibiotics, including bacillomycin, iturin, and surfactin. Chemical analysis of the cultivation of B. siamensis YC-9 resulted in the isolation of five metabolites, including hexadecanoic acid ( 1 ), cyclo-(L-phenylalanylglycine) ( 2 ), cyclo-(L-trans-Hyp-L-Leu) ( 3 ), C 15 -surfactin ( 4 ), and macrolactin A ( 5 ), the structures of which were identified by the analysis of NMR spectroscopic data and MS. Among them, the compound 4 showed significant antifungal activity against conidial germination of FOC with an IC 50 value of 5.1 μg/ml, which was comparable to that of the positive control, cycloheximide (IC 50 value of 2.6 μg/ml). Based on these findings, this study suggests that termite-nest associated B. siamensis YC-9 could be a potential biological control agent for integrated control of soil-borne diseases like cucumber Fusarium wilt.