Characterization of secondary metabolites from an Arizona native entomopathogenic bacterium, Photorhabdus luminescens sonorensis, and their use in biological control

A great body of knowledge exists illustrating how symbiotic microorganisms produce a broad spectrum of compounds with potential for agricultural applications. Entomopathogenic bacteria in the genus Photorhabdus represent a rich source of novel bioactive molecules with insecticidal, nematicidal, antibiotic and antimycotic properties. Photorhabdus are motile Gram-negative bacteria that have a mutualistic association with Heterorhabditis nematodes (Heterorhabditidae). The nematode vectors the bacteria from one insect host to another, while providing shelter to the bacteria from soil stressors and antagonists. At present, three Photorhabdus spp. have been identified: P. luminescens, P. temperata and P. asymbiotica, with many subspecies described for each taxon. Due to their high pathogenicity to various insect orders, the nematode- bacteria system has been widely used in biological control and integrated pest management around the world. Recent genome analysis showed that 6% of the genome of P. luminescens encodes for secondary metabolites. This work aims to identify and characterize secondary metabolites from an Arizona native entomopathogenic bacterium, Photorhabdus luminescens sonorensis, as a source of novel bioactive molecules for agricultural bioprospecting. Chemical characterization of the bacterial metabolites was conducted through TLC, HPLC, and MS using crude fermentation extracts. Five other strains of Photorhabdus sp. were also tested for comparison. The potential of these compounds as insecticides was evaluated by testing contact and oral toxicity on neonates and 2nd instar Helicoverpa zea. This study establishes the foundation for long term research in genetic and genomic studies of this organism, and its role in insect pest management.