Morphological, molecular and ecological characterization of a native isolate of Steinernema feltiae (Rhabditida: Steinernematidae) from southern Chile

Abstract

Background Steinernema feltiae is an entomopathogenic nematode used in biological control programs with a global distribution. Populations of this species show phenotypic plasticity derived from local adaptation and vary in different traits, such as location and host penetration. The aim of this work was to describe a Chilean isolate of this nematode species, using integrative approaches. Methods Nematode morphological and morphometric studies were conducted along with molecular analysis of nuclear genes. The symbiotic bacterium was also identified by sequencing the 16S rRNA gene. Some ecological characteristics were described, including the temperature requirements for the nematode life cycle and the effect of soil water content for optimal reproduction. Results Morphometric characterization revealed a large intra-specific variability. The isolate identity was also corroborated with the analysis of nuclear genes. Based on the 16S gene, its symbiont bacteria, Xenorhabdus bovienii, was identified. The lowest, optimal and highest temperatures found to limit the infestation and reproduction on Galleria mellonella were 10, 20 and 30 °C, respectively; the emergence from the host larvae occurred approximately 10 days after inoculation. Differences were observed in offspring, and 120 infective juveniles (IJ)/larva was the most prolific dose at 20 °C. The soil water content did not affect the number of IJ invaders, penetration efficacy and IJ emergence time or offspring per larva, but it caused a delay in achieving full mortality at the permanent wilting point with respect to saturation and field capacity. Conclusions For the first time, a Chilean isolate of S. feltiae is described in detail considering morphological, molecular and ecological aspects. The isolate was shown to be efficient in soil containing water, with optimal temperatures ranging from 15 to 25 °C for host infestation and production of an abundant offspring; these characteristics would allow its potential use as control agents in a wide geographical area of the country.

Molecular Identification and Phylogenetic Diversity of Native Entomopathogenic Nematodes, and Their Bacterial Endosymbionts, Isolated from Banana and Plantain Crops in Western Colombia

“…Recently, similar approaches were carried out in the isolation of indigenous EPNs for pest control, targeting local adaption for biological control [27,89,94,95]. These agents provide promising results to reduce intense chemical pest management [89,96].…”

“…These target barcode regions comprise nuclear ribosomal loci (ITS, SSU, and LSU) and mitochondrial genes (COI, 12S, and NAD). Among these, ribosomal loci represent a major tool for investigating and identifying nematodes species [72,74,89,95,99,101,103]. They also represent the main source of information in the databases, providing more reliability for species identification [74,99,101].…”

“…Later on, Stock and Blair [35] related X. szentirmaii as the mutualistic bacteria associated with S. costaricense; nevertheless, this association was not supported by other studies [34,74,117]. The isolation and identification of the EPN's bacterial symbionts has received special attention, not only for their entomopathogenic efficiency [27,29,31,33,39,89,[94][95][96][118][119][120][121][122]] but also for their potential applicability as antimicrobials [123], even targeting drug-resistant bacteria [34], their richness in metabolites with agricultural interest [32,124], and their abundance of peptides with functionality for cancer treatment [125].…”

“…The phylogenetic studies carried out on EPN have proven to be conflicting since the application of several descriptors, morphological [133,134] and molecular [62,[72][73][74]95,104,123], has provided alternative inferences to the understanding of EPN's natural history. Extensive exploration has focused on the search for the optimal loci applicable for species identification and delimitation.…”

“…Extensive exploration has focused on the search for the optimal loci applicable for species identification and delimitation. Since the studies of Szalanski et al [135], who identified agreement between morphological and molecular phylogenies, further studies converged in the selection of the ITS and LSU ribosomal loci as the appropriate markers [70,72,95,104,116,136], currently denoted as DNA barcodes for EPN. Mitochondrial loci have tentatively been used as optional barcoding regions, yet significant inconsistencies with morphological and ribosomal hypotheses have limited the factual utilization of these loci.…”