Nematophin, an Antimicrobial Dipeptide Compound From Xenorhabdus nematophila YL001 as a Potent Biopesticide for Rhizoctonia solani Control

Abstract

This study was conducted to purify and identify metabolites of antimicrobial activity against phytopathogens from <i>Xenorhabdus nematophila</i> YL001. Three dipeptide compounds were purified from its cell-free cultural broth and identified as (±)-nematophin, <i>cyclo</i> (L-Pro-Gly), and <i>N</i>, <i>N'</i>-dimethyl-<i>cyclo</i> (L-Phe-L-Leu). Nematophin demonstrated a wider antifungal spectrum than the other two compounds. It also exhibited strong inhibitory effects on mycelial growth of <i>Rhizoctonia solani</i> and <i>Phytophthora infestans</i> with EC₅₀ values of 40.00 and 51.25 μg/ml, respectively. Its (<i>S</i>)-configuration structure [(+)-nematophin] was also synthesized and exhibited higher antimicrobial activity than the enantiomeric mixture. The detached leaf assay revealed that nematophin possessed significant preventive and curative efficacy against <i>R. solani</i> on broad bean leaves showing corresponding control efficacies of 93.01 and 94.93% at 1,000 μg/ml, comparable to those of a chemical fungicide (carbendazim) at 500 μg/ml. Additionally, the pot experiments indicated that nematophin could effectively inhibit the disease extension on rice and broad bean plants caused by <i>R. solani</i>. Nematophin also exerted some adverse influences on the sclerotial development of <i>R. solani</i> by dramatically suppressing their formation and maturation at 40.00 μg/ml, as well as their germination at 15.00 μg/ml. Morphological and ultrastructural observations showed that the hyphae of <i>R. solani</i> became twisted, shriveled, and deformed at the growing points after exposure to nematophin at 40.00 μg/ml, and that the subcellular fractions also became abnormal concurrently, especially the mitochondrial structure. These results indicate that nematophin has great potential to be used as a bio-pesticide in agricultural production.