Characterization and pathogenicity of symbiotic bacteria associated with entomopathogenic nematode: Steinernema species KALRO

Abstract

The soil inhibiting entomopathogenic nematodes (EPNs), in the family Steinernematidae and Heterorhabditidae, are useful insect biological control agents. They have been used in the management of economically important crop pests. The EPNs are mutually associated with symbiotic bacteria genus Xenorhabdus and Photoharbdus respectively. The study aimed to isolate, characterize and evaluate the pathogenicity of symbiotic bacteria associated with EPN Steinernema sp. Kalro (Accession MW151701). The EPN Steinernema sp. Karlo was multiplied using the insect baiting technique. Its bacteria symbiont was isolated and characterized based on microscopic, biochemical, and physiological features like Gram staining, urease, motility test, and glucose fermentation test).  Molecular identification and phylogenetic analysis were performed on 16S rDNA nucleotide sequence. Pathogenicity of the bacteria isolate was evaluated against Tuta absoluta larvae with mortality data recorded after 24 and 48hours of exposure to the bacterial cell suspension. The bacteria were found to be motile and glucose fermentation positive. Sequence analysis of 16S rDNA region resulted in 1500bp sequence with maximum similarity of between 97 and 98.93%, with Xenorhabdus spp Accessions from Genbank. It closely matched to Xenorhabdus sp. My8NJ with 98.93% similarity (Accession AB507811.1). Mean percent larval mortality of 68±4.9 and 88±8.0 in the lowest cell suspension was observed in 24 and 48h of exposure. It’s concluded that, the symbiotic bacteria associated with Steinernema sp. Kalro is Xenorhabdus sp. strain Kalro Genbank Accession MW245845. The bacteria is a potential biological control agent against Tuta absoluta larvae. Further classification of the bacteria to species level and pathogenicity trials in the screen house and field are recommended.