Characterization and insecticidal potential of native Moroccan bacteria associated with entomopathogenic nematodes against Galleria mellonella

Abstract

Entomopathogenic nematodes (EPNs) harbour bacterial associates that contribute to insect pathogenicity and may provide bioactive traits, yet the culturable bacterial fraction associated with Moroccan EPNs remains poorly characterized. We recovered 19 purified, phenotypically stable isolates and characterized them using colony morphology, Gram reaction, 16S rRNA sequencing, qualitative enzymatic screening, and an injection bioassay in Galleria mellonella . The collection included the primary symbionts Xenorhabdus bovienii , Photorhabdus laumondii subsp. laumondii , and Photorhabdus thracensis , together with several co-associated bacterial taxa. Protease and lipase reactions were the most frequently detected qualitative traits. Longitudinal grouped-binomial analysis identified significant overall effects of bacterial isolate and observation time. Nine isolates caused 100% cumulative mortality at 120 h, whereas mortality among the five least pathogenic isolates ranged from 0.8% to 25.0%. Among isolates reaching median mortality, LT₅₀ estimates ranged from 15.1 to 77.9 h, five isolates did not reach 50% mortality within 120 h. Exploratory point-biserial analyses identified positive associations between detectable lipase and lecithinase reactions and mortality at 72 h, without establishing causality. Gower-distance principal coordinate analysis revealed broad phenotypic variation and substantial overlap between primary symbionts and co-associated isolates. These findings provide a preliminary basis for prioritizing native isolates for quantitative biochemical characterization, biosafety assessment, and validation against defined target pests under natural exposure conditions.