Volatile organic compounds produced by Paenibacillus polymyxa J2-4 exhibit toxic activity against Meloidogyne incognita

Separation and identification of nematicidal active compounds in culture filtrate of Streptomyces aquilus JXGZ01 based on metabolomic analysis

BACKGROUND

Meloidogyne incognita is one of the pathogenic nematodes with the widest range and most serious damage, which can infest many food and cash crops. We screened a strain of Streptomyces aquilus JXGZ01, whose culture filtrate showed excellent nematicidal activity and egg hatching inhibition activity against M. incognita. In this study, we performed metabolomic analysis of the culture filtrate of this strain.

RESULTS

The data showed that of the total 304 differential metabolites, 244 were significantly up-regulated and 60 were significantly down-regulated. Seven compounds with large fold changes were selected from the up-regulated metabolites to test the nematicidal activity against M. incognita. The mortality of M. incognita in both 5 and 10 mg mL-1 of 4-acetylaminobutyric acid was more than 85%. The mortality of M. incognita in both 10 and 100 mg mL-1 of (R)-(-)-2-phenylglycinol was more than 70%. The mortality rate of M. incognita in 100 mg of N-acetyl-l-glutamic acid was 78.25%. In addition, the hatching inhibition rate of egg masses were more than 90% for both 5 and 10 mg mL-1 of 4-acetylaminobutyric acid. The hatching inhibition rate of egg masses were more than 80% for 100 mg and 10 mg (R)-(-)-2-phenylglycinol. The hatching inhibition rate of 100 mg N-acetyl-l-glutamic acid on eggs was 93.47%.

CONCLUSION

The results demonstrate that S. aquilus can be a candidate microorganism for the biological control of M. incognita, and its metabolites 4-acetylaminobutyric acid and (R)-(-)-2-phenylglycinol had great potential as nematicides. © 2025 Society of Chemical Industry.

Eco-Friendly Biomass Production and Identification of Active Compounds of Paenibacillus polymyxa EB.KN35 with Potent Anti-Fusarium oxysporum Effect

Fusarium oxysporum is a fungal plant pathogen for over 100 agricultural crop species. There are strategies for managing Fusarium wilt, including antagonistic bacteria that offer a promising and sustainable effect. In this work, among the various endophytic bacterial strains, Paenibacillus polymyxa EB.KN35 was selected as the best antifungal strain against F. oxysporum. For eco-friendly biomass production of this bacterium, some agricultural byproducts were tested for cultivation, and a soybean processing byproduct (SPBP) was found to be a suitable C/N source for P. polymyxa EB.KN35 fermentation. The utilization of a 14 L bioreactor system for P. polymyxa EB.KN35 fermentation achieved a high biomass productivity (3.46 × 1011 CFU/mL) in a short time (8 h). In bioactive compound analysis, EB.KN35 was found to be secreting several plant growth-promoting compounds such as GA3, IAA, kinetin, and zeatin (via HPLC) and eleven volatile compounds (via GC-MS). The docking study indicated that some volatile compounds (1, 2, 4, and 9) may play a significant role in inhibiting F. oxysporum. The study results highlight the potential for reusing a soybean processing byproduct as a C/N source for the bioproduction of P. polymyxa EB.KN35 with potential use as a biocontrol agent and biofertilizer.

Nematicidal activity of pyrazine compounds against Meloidogyne incongnita, Burshaphelenchus xylophilus, and Aphelenchoides besseyi

The increase of plant parasitic nematode resistance poses a great threat to agricultural and forestry production. To search for nematicides with novel mechanism of action, nematicidal activity of the 29 pyrazine compounds were tested. Compound C2 showed excellent nematicidal activity against Bursaphelenchus xylophilus, Meloidogyne incongnita, and Aphelenchoides besseyi, with LC50 values were 2.3, 3.3, and 10.6 mg/L, respectively, and the pot experiment showed that C2 reduced the number of tomato roots knots to a certain extent. In addition, C2 significantly inhibited egg hatching, locomotion and reproductive ability of B. xylophilus, and also reduced the levels of protein and antioxidant enzyme activity to some extent, and the indexes related to oxidative stress showed an increasing trend after treatment. The novel chemical structure of compound D was designed and synthesized based on the lead compound C2 by the scaffold hopping strategy. Interestingly, compound D also has excellent nematicidal activity. Compound D can be used as an excellent scaffold in the discovery of novel nematicides and we will continue to work on the optimization and modification of this scaffold structure in the future.

Paenibacillus polymyxa J2-4 induces cucumber to enrich rhizospheric Pseudomonas and contributes to Meloidogyne incognita management under field conditions

BACKGROUND

Root knot nematodes (RKNs) pose a great threat to agricultural production worldwide. The bacterial nematocides have received increasing attention due to their safe and efficient control against RKNs. Here, we investigated the biocontrol efficacy of Paenibacillus polymyxa J2-4 against Meloidogyne incognita in the field and analyzed the rhizosphere microbiome of cucumber under nematode infection after application of the J2-4 strain. Furthermore, a biomarker strain of Pseudomonas spp. was isolated from the J2-4-inoculated rhizosphere soil, and its nematocidal activity and growth-promoting effect on host plants were determined. In addition, chemotaxis assay of P. fluroescens ZJ5 toward root exudates was carried out.

RESULTS

The field experiment demonstrated that P. polymyxa J2-4 could effectively suppressed gall formation in cucumber plants, with the galling index reduced by 67.63% in 2022 and 65.50% in 2023, respectively, compared with controls. Meanwhile, plant height and yield were significantly increased in J2-4 treated plants compared with controls. Metagenomic analysis indicated that J2-4 altered the rhizosphere microbial communities. The relative abundance of Pseudomonas spp. was notably enhanced in the J2-4 group, which was consistent with Linear discriminant analysis Effect Size results that Pseudomonas was determined as one of the biomarkers in the J2-4 group. Furthermore, the ZJ5 strain, one of the biomarker Pseudomonas strains, was isolated from the J2-4-inoculated rhizosphere soil and was identified as Pseudomonas fluorescens. In addition, P. fluorescens ZJ5 exhibited high nematicidal activity in vitro and in vivo, with 99.20% of the mortality rate of M. incognita at 24 h and 69.75% of gall index reduction. The biocontrol efficiency of the synthetic community of ZJ5 plus J2-4 was superior to that of any other single bacteria against M. incognita. Additionally, ZJ5 exhibited great chemotaxis ability toward root exudates inoculated with J2-4.

CONCLUSION

Paenibacillus polymyxa J2-4 has good potential in the biological control against M. incognita under field conditions. Enrichment of the beneficial bacteria Pseudomonas fluorescens ZJ5 in the J2-4-inoculated rhizosphere soil contributes to M. incognita management. © 2024 Society of Chemical Industry.

Biocontrol activity and potential mechanism of Bacillus cereus G5 against Meloidogyne graminicola

Root-knot nematodes (Meloidogyne spp.) are highly destructive pests that cause significant yield losses annually. Biological control of nematodes has emerged as a potential alternative in sustainable agriculture. In this study, we originally isolated Bacillus cereus G5 from the rhizosphere soil of rice (Oryza sativa). Treatment with the fermentation supernatant of G5 in vitro demonstrated high toxicity to second-stage juveniles (J2) of Meloidogyne graminicola and remarkably inhibited egg hatching. Moreover, G5 steadily colonized rhizosphere soil and rice seedlings, and exhibited excellent biocontrol efficacy against M. graminicola under greenhouse conditions. Notably, the volatile organic compounds (VOCs) produced by G5 displayed high fumigant activity against M. graminicola. The G5 VOCs efficiently reduced the gall index and nematode population in rice roots, while also promoting rice growth in double-layered pot tests. Additionally, the expression of defense genes involved in the salicylic acid (OsNPR1, OsWRKY45, OsPAL1), jasmonic acid (OsJaMYB, OsAOS2) and ethylene (OsACS1) signalling pathways was significantly upregulated in rice seedlings treated with G5 VOCs. This suggests that G5 VOCs contribute to eliciting plant defense responses. Furthermore, we identified 14 major VOCs produced by G5 using solid-phase micro-extraction gas chromatography and mass spectrometry (SPEM-GC-MS). Notably, allomatrine, morantel, 1-octen-3-ol and 3-methyl-2-butanol displayed strong contact nematicidal activity. Among these, only 1-octen-3-ol demonstrated fumigant activity against J2s of M. graminicola, with an LC50 value of 758.95 mg/L at 24 h. Overall, these results indicated that the B. cereus G5 and its synthetic VOCs possess high potential as biocontrol agents for managing root-knot nematodes.

3-(Methylthio)Propionic Acid from Bacillus thuringiensis Berliner Exhibits High Nematicidal Activity against the Root Knot Nematode Meloidogyne incognita (Kofoid and White) Chitwood

Root knot nematodes cause serious damage to global agricultural production annually. Given that traditional chemical fumigant nematicides are harmful to non-target organisms and the environment, the development of biocontrol strategies has attracted significant attention in recent years. In this study, it was found that the Bacillus thuringiensis Berliner strain NBIN-863 exhibits strong fumigant nematicidal activity and has a high attraction effect on Meloidogyne incognita (Kofoid and White) Chitwood. Four volatile organic compounds (VOCs) produced by NBIN-863 were identified using solid-phase microextraction and gas chromatography-mass spectrometry. The nematicidal activity of four VOCs, namely, N-methylformamide, propenamide, 3-(methylthio)propionic acid, and phenylmalonic acid, was detected. Among these compounds, 3-(methylthio)propionic acid exhibited the highest direct contact nematicidal activity against M. incognita, with an LC50 value of 6.27 μg/mL at 24 h. In the fumigant bioassay, the mortality rate of M. incognita treated with 1 mg/mL of 3-(methylthio)propionic acid for 24 h increased to 69.93%. Furthermore, 3-(methylthio)propionic acid also exhibited an inhibitory effect on the egg-hatching of M. incognita. Using chemotaxis assays, it was determined that 3-(methylthio)propionic acid was highly attractive to M. incognita. In pot experiments, the application of 3-(methylthio)propionic acid resulted in a reduction in gall numbers, decreasing the number of galls per gram of tomato root from 97.58 to 6.97. Additionally, the root length and plant height of the treated plants showed significant increases in comparison with the control group. The current study suggests that 3-(methylthio)propionic acid is a novel nematicidal virulence factor of B. thuringiensis. Our research provides evidence for the potential use of NBIN-863 or its VOCs in biocontrol against root knot nematodes.