Intergrated metagenomics and metabolomics analysis discovers nematicidal microbes, enzymes and metabolites from the plant rhizosphere microbiota
Authors: Zhao Xiuyun , Lin Changchun , Yuan Wenfang , Ruan Song , Qi Gaofu , Wang Rui , Tan Jun 
Published: July 2021

Abstract
Background: Meloidogyne incognita infestation has led to huge economic loss worldwide. Nematicidal microorganisms provide an effective strategy to control M. incognita . In order to find microorganisms and new metabolites with high nematicidal activity, we collected M. incognita - infested tobacco rhizosphere soils and non-infested rhizosphere soils, and investigated functional genes, microbial community and network, and metabolites via metagenomics and metabolomics analyses. Results: Rhizosphere microbial composition, function, network and metabolites were altered accompanying with M . incognita infestation. Abundances of nematicidal microorganisms, metabolites, antibiotics and extracellular enzymes’ genes in the non-infested rhizosphere microbiota were higher than those in M. incognita -infested rhizosphere microbiota. Abundances of functions genes involved in secondary metabolites biosynthesis and carbohydrate transport and metabolism in the non-infested rhizosphere microbiota were higher than M. incognita -infested rhizosphere microbiota. Contents of 102 metabolites were different in the two rhizosphere microbiota. Contents of 35 metabolites (acetophenone, indole-3-acetic acid, etc.) in the non-infested rhizosphere microbiota were higher than those in M . incognita -infested rhizosphere microbiota. Acetophenone showed high nematicidal (LC 50 = 0.66 μg/ml) and repellent activities against M. incognita . Co-occurrence network analyses found Bacillus showed a stronger positive correlation with acetophenone. Nematicidal microorganisms were isolated from soils, and one isolate of B . amyloliquefaciens W1 produced acetophenone. Exposing J2 larvae of M. incognita to liquid culture filtrate of W1 resulted in a mortality rate of 98.8% after 24 h. Other isolates such as Aspergillus , Achromobacter , Acinetobacter , Bacillus , Burkholderia , Comamonas , Enterobacter , Lysobacter , Microbacterium , Paenibacillus , Pantoea , Pseudomonas , Streptomyces and Variovorax produced extracellular nematicidal enzymes. Conclusions: M eloidogyne incognita -infested rhizophere microbiota differed in microbial community composition, network structure, function genes and metabolites contents from the non-infested rhizosphere microbiota. Abundances of nematicidal microorganisms and metabolites, and genes involved in secondary metabolites biosynthesis and carbohydrate metabolism in the non-infested rhizosphere microbiota were higher than those in M . incognita -infested rhizosphere microbiota. Network complexity in M . incognita -infested rhizosphere microbiota was lower than that in non-infested rhizosphere microbiota. Keystone microorganisms were also different between these two networks. Acetophenone was identified as a new nematicidal compound with high activity to kill and repel M. incognita , and B. amyloliquefacens W1 isolated from non-infested soil produced acetophenone against M. incognita .