Abstract
Abstract
A native entomopathogenic nematode isolate,
Heterorhabditis indica
Che4.1, was recovered from soils in Valencia (Spain), and its symbiotic bacterium,
Photorhabdus akhurstii
Che4.1, was isolated and characterized. Nematode identification was confirmed by ITS and 28S rDNA sequencing, while genome-based analyses supported the taxonomic assignment of the bacterial symbiont. The nematode–bacterium complex exhibited insecticidal activity against
Spodoptera exigua
and
Spodoptera littoralis
.
H. indica
Che4.1 showed an LC₅₀ of 53.7 infective juveniles (IJs)/mL against
S. exigua
, comparable to that of the commercial reference Larvanem
®
(54.3 IJs/mL). Against
S. littoralis
, Che4.1 exhibited an approximately twofold lower LC₅₀ than Larvanem
®
(77.3 versus 155.9 IJs/mL), with non-overlapping 95% confidence intervals. The complete genome of
P. akhurstii
Che4.1 consists of a single circular chromosome of 5.66 Mb encoding a diverse repertoire of putative virulence factors, including toxin complex (Tc) components, YenTc-like proteins, Mcf toxins, App-family proteins, Pra/Prb proteins, and chitinases, together with several predicted secondary metabolite biosynthetic gene clusters. LC– MS/MS analyses of bacterial culture supernatants and infected insect cadavers detected multiple predicted virulence-associated proteins, including Tc-related, YenTc-like, App-family, and Pra/Prb proteins. In addition, bacterial cell-free supernatants caused 68.8–81.3% mortality in
S. exigua
neonates under laboratory conditions. Together, these findings reveal a diverse repertoire of potential virulence determinants in
P. akhurstii
Che4.1 and demonstrate the insecticidal potential of its native nematode–bacterium complex. The performance of
H. indica
Che4.1 relative to a commercial reference supports further evaluation of this isolate for biological control of
Spodoptera
spp., particularly under greenhouse and field conditions.