No abstract

Root knot nematodes (RKNs) are the world's most damaging plant-parasitic nematodes (PPNs), and they can infect almost all crops. At present, harmful chemical nematicides are applied to control RKNs. Using microbial nematicides has been proposed as a better management strategy than chemical control. In this study, we describe a novel nematicidal bacterium named Alcaligenes faecalis ZD02. A. faecalis ZD02 was isolated from Caenorhabditis elegans cadavers and has nematostatic and nematicidal activity, as confirmed by C. elegans growth assay and life span assay. In addition, A. faecalis ZD02 fermentation broth showed toxicity against C. elegans and Meloidogyne incognita. To identify the nematicidal virulence factor, the genome of strain ZD02 was sequenced. By comparing all of the predicted proteins of strain ZD02 to reported nematicidal virulence factors, we determined that an extracellular serine protease (Esp) has potential to be a nematicidal virulence factor, which was confirmed by bioassay on C. elegans and M. incognita. Using C. elegans as the target model, we found that both A. faecalis ZD02 and the virulence factor Esp can damage the intestines of C. elegans. The discovery that A. faecalis ZD02 has nematicidal activity provides a novel bacterial resource for the control of RKNs. P lant-parasitic nematodes (PPNs) are an important agricultural pest of many crops, and they cause agricultural losses amounting to an estimated $157 billion worldwide every year (1, 2). Root knot nematodes (RKNs; Meloidogyne spp.) are the most damaging crop PPNs, and they are capable of infecting almost all crops (2, 3). The management of RKNs is more difficult than that of other pests because RKNs are obligate root parasites of thousands of plant species, and most of the life cycle of RKNs is spent as parasites in the host roots (2, 4). The current means of controlling RKNs relies on chemical nematicides, which are often toxic and harmful to humans and the environment (3). In addition, chemical nematicides are generally expensive and cannot provide longterm RKN suppression (5).Biological control of RKNs is a better management strategy that avoids the potential environmental problems associated with the chemical control of RKNs. Indeed, the utilization of beneficial bacterial nematicides has been proposed as a sustainable alternative for RKN management, and bacterial nematicides are also regarded as economical and ecologically friendly nematicides for the control of RKNs (3, 6). Currently, for the bacterial control of RKNs, many problems remain, one of which is that nematicidal bacteria are relatively scarce. Only a few bacteria have been reported to possess nematicidal activity and to show potential for the biological control of RKNs. The typical nematicidal bacteria are Bacillus, Pseudomonas, and Pasteuria species (4, 7). Identifying novel nematicidal bacteria has become urgent for the bacterial control of RKNs and is of vital practical and economic significance.However, until now, it has been a challenge to isolate novel nematici...