Soil-borne nematodes establish close associations with several bacterial species. Whether they confer benefits to their hosts has been investigated in only a few nematode-bacteria systems. Their ecological function, therefore, remains poorly understood. In this study, we isolated several bacterial species from rhabditid nematodes, molecularly identified them, evaluated their entomopathogenic potential onGalleria mellonellalarvae, and measured immune responses ofG.mellonellalarvae to their infection. Bacteria were isolated fromAcrobeloidessp.,A.bodenheimeri,Heterorhabditis bacteriophora,Oscheius tipulae, andPristionchus maupasinematodes. They were identified asAcinetobactersp.,Alcaligenessp.,Bacillus cereus,Enterobactersp.,Kaistiasp.,Lysinibacillus fusiformis,Morganella morganiisubsp.morganii,Klebsiella quasipneumoniaesubsp.quasipneumoniae, andPseudomonas aeruginosa. All bacterial strains were found to be highly entomopathogenic as they killed at least 53.33%G.mellonellalarvae within 72h post-infection, at a dose of 10⁶CFU/larvae. Among them,Lysinibacillus fusiformis,Enterobactersp.,Acinetobactersp., andK.quasipneumoniaesubsp.quasipneumoniaewere the most entomopathogenic bacteria. Insects strongly responded to bacterial infection. However, their responses were apparently little effective to counteract bacterial infection. Our study, therefore, shows that bacteria associated with soil-borne nematodes have entomopathogenic capacities. From an applied perspective, our study motivates more research to determine the potential of these bacterial strains as biocontrol agents in environmentally friendly and sustainable agriculture.

A survey to collect soil nematodes with potential to controlCeratitis capitataflies was carried out in different locations in Tunisia. Several nematode isolates were recovered, laboratory colonies were established, and their taxonomic identities were determined based on molecular methods. Among all the recovered nematode isolates, two of them,Oscheius tipulaeTC2 and OC2, were evaluated for their capacity to controlC.capitataflies and for their ability to kill and reproduce onGalleria mellonellalarvae. Our results show a great potential of these two isolates as biocontrol agents as they killC.capitataeggs and pupae and interfere with the metamorphosis ofC.capitatalarvae. More specifically, TC2 and OC2 nematodes killed 39 and 31% ofC.capitataeggs, respectively, impaired the metamorphosis of up to 77% and up to 67% ofC.capitatalarvae, respectively, and killed up to 66% and up to 58% ofC.capitatapupae, respectively. The efficacy of TC2 and OC2 nematodes was particularly high onC.capitatapupae, and significant insect mortalities were observed even at concentrations of 1 and 5 nematodes/pupae, respectively. We also found that TC2 and OC2 nematodes efficiently kill and reproduce inG.mellonellalarvae, suggesting that these insects could be used for mass-multiplication of these nematodes. These results reveal the potential ofO.tipulaeto complement integrated pest management programs againstC.capitataflies.

Four bacterial strains, A-IN1^T, A-TC2^T, E-TC7^T, and K-TC2^T, isolated from soil-borne nematodes of the species Oscheius tipulae and Acrobeloides bodenheimeri, were found to represent new species of the genera Acinetobacter, Alcaligenes, Enterobacter, and Kaistia, respectively. In this study, we described these new species using a polyphasic taxonomic approach that included whole-genome and whole-proteome phylogenomic reconstructions, core genome sequence comparisons, and phenotypic characterization. Phylogenomic reconstructions using whole-genome and whole-proteome sequences show that A-IN1^T is closely related to Acinetobacter guillouiae DSM 590^T and to Acinetobacter bereziniae LMG 1003^T. The dDDH values between A-IN1^T and these latest strains are 25.1 and 39.6%, respectively, which are below the 70% divergence threshold for prokaryotic species delineation. A-TC2^T is closely related to Alcaligenes faecalis subsp. faecalis DSM 30030^T and to Alcaligenes faecalis subsp. phenolicus DSM 16503^T. The dDDH values between A-TC2^T and these latest strains are 47.0 and 66.3%, respectively. In addition, the dDDH values between Alcaligenes faecalis subsp. faecalis DSM 30030^T, Alcaligenes faecalis subsp. phenolicus DSM 16503^T, and Alcaligenes faecalis subsp. parafaecalis are always lower than 70%, demonstrating that the three strains represent species within the genus Alcaligenes rather than subspecies within Alcaligenes faecalis. E-TC7^T is closely related to Enterobacter kobei DSM 13645^T, Enterobacter chuandaensis 090028^T, and to Enterobacter bugandensis STN0717-56^T. The dDDH values between E-TC7^T and these strains are 43.5, 42.9, and 63.7%, respectively. K-TC2^T is closely related to Kaistia terrae DSM 21341^T and to Kaistia defluvii JCM 18034^T. The dDDH values between these strains are 29.2 and 30.7%, respectively. Several biochemical tests allow to differentiate the type strains of the newly described species from the type strains of their more closely related species. Based on the results of this polyphasic taxonomic approach, the following new species are proposed: Acinetobacter nematophilus sp. nov. with A-IN1^T (=CCM 9231^T =CCOS 2018^T) as the type strain, Alcaligenes nematophilus sp. nov. with A-TC2^T (=CCM 9230^T =CCOS 2017^T) as the type strain, Enterobacter nematophilus sp. nov. with E-TC7^T (=CCM 9232^T =CCOS 2020^T) as the type strain, and Kaistia nematophila sp. nov. with K-TC2^T (=CCM 9239^T =CCOS 2022^T) as the type strain. In addition, we propose the elevation of Alcaligenes faecalis subsp. faecalis, Alcaligenes faecalis subsp. parafaecalis, and Alcaligenes faecalis subsp. phenolicus to the species level. Therefore, we propose the creation of Alcaligenes parafaecalis sp. nov. with DSM 13975^T as the type strain, and Alcaligenes phenolicus sp. nov. with DSM 16503^T as the type strain. Our study contributes to a better understanding of the biodiversity and phylogenetic relationships of bacteria associated with soil-borne nematodes.

Grapevine fanleaf virus (GFLV) is one of the most severe virus diseases of grapevines, causing fanleaf degeneration that is transmitted by Xiphinema index. This paper aims to isolate Xiphinema species from Tunisian vineyard soil samples and assess their ability to acquire and transmit GFLV under natural and controlled conditions. Based on morphological and morphometric analyses, Tunisian dagger nematodes were identified as X. index and Xiphinema italiae. These results were confirmed with molecular identification tools using species-specific polymerase chain reaction primers. The total RNA of GFLV was extracted from specimens of Xiphinema and amplified based on real-time polymerase chain reaction using virus-specific primers. Our results showed that X. index could acquire and transmit the viral particles of GFLV. This nepovirus was not detected in X. italiae, under natural conditions; however, under controlled conditions, this nematode was able to successfully acquire and transmit the viral particles of GFLV.

Rhynchophorus ferrugineusOlivier (Coleoptera: Curculionidae) red palm weevils are often reported in association with different organisms including nematodes. The significance of this interaction and whether nematodes can influence their life‐history traits is unclear. We collectedRhynchophorus ferrugineusred palm weevils at different developmental stages and locations in Tunisia, observed and dissected them in search for nematodes and other interacting organisms, established laboratory colonies and identified the nematodes associated with them, and conducted nematode–insect interaction assays to determine the capacity of the nematodes to influence their life‐history traits. We observedBeauveria bassianafungi in larvae, nymph, and adults;CentrouropodaandUroobovellaacari associated with the adults, andTeratorhabditis synpapillatanematodes associated with larvae and adults. Nematode–insect interaction bioassays revealed thatT.synpapillatanematodes reduce the lifespan of the insect larvae in a population‐dependent manner, but do not influence the lifespan of adults. Our study uncovers an important factor that may determine population dynamics of this important palm pests and provides evidence to conclude that these organisms establish a parasitic relationship, rather than a phoretic relationship.

Tylenchulus semipenetrans Cobb, is a parasitic nematode of citrus, causing significant reduction in citrus growth and yield. Biological antagonists including bacteria and fungi have been used to control citrus nematodes. Citrus rhizosphere bacteria were collected from mature orchards in Tunisia and they have been studied to evaluate their nematicidal potentials on citrus nematode and abilities to stimulate plant root growth. Sixty bacterial strains isolated from egg masses of citrus nematode, citrus roots and associated to nematode trapping fungi, were tested for their abilities to parasitize T. semipenetrans and their impact on citrus growth parameters. The data analysis revealed that Bacillus weihenstephanensis, Lysinibacillus sphaericus, Bacillus subtilis, Bacillus thuringiensis, Bacillus pumilus and Bacillus cereus showed the highest effectiveness on T. semipenetrans juvenile (J2) causing up to 85% mortality of juveniles (J2) after 6 days of exposure in vitro. B. subtilis, B. amyloliquefaciens, B. pumilus and B. weihenstephanensis also inhibited egg hatching of citrus nematode in vitro. Furthermore, the majority of these rhizobacteria significantly stimulated citrus growth parameters. The application of B. weihenstephanensis, B. cereus, B. mycoides, B. thuringiensis, L. sphaericus, and Alcaligenes faecalis stimulated sour orange root growth in vitro compared to the control. Citrus rhizosphere bacteria must be studied further due to their diversity, abundance, and ability to effectively control T. semipenetrans.