•Steinernema-Xenorhabdus-insect interaction is an ideal model to investigate symbiosis.•Insect virulence and reproductive fitness of these partners is tightly associated and codependent.•The level of ...specificity and dependence varies from facultative to obligate.•The insect host serves as the environment for mutualism maintenance.
Entomopathogenic nematodes in the genus Steinernema (Nematoda: Steinernematidae) have a mutualistic relationship with Xenorhabdus bacteria (Gram-negative Enterobacteriaceae). This partnership however, is pathogenic to a wide range of insect species. Because of their potent insecticidal ability, they have successfully been implemented in biological control and integrated pest management programs worldwide. Steinernema-Xenorhabdus-insect partnerships are extremely diverse and represent a model system in ecology and evolution to investigate symbioses between invertebrates and microbes. The reproductive fitness of the nematode-bacterium partnership is tightly associated, and maintenance of their virulence is critical to the conversion of the insect host as a suitable environment where this partnership can be perpetuated.
Root-knot nematodes (RKNs) cause significant economic damage to crop plants, spurring demand for safe, affordable, and sustainable nematicides. A previous study by our research team showed that the ...combination of two nematicidal secondary metabolites (SMs) derived from
bacteria,
-cinnamic acid (
-CA) and (4E)-5-phenylpent-4-enoic acid (PPA), have a synergistic effect against RKNs
. In this study, we considered in planta assays to assess the effects of this SM mixture on the virulence and reproductive fitness of the RKN
in a cowpea. Factorial combinations of five
-CA + PPA concentrations (0, 9.0, 22.9, 57.8, and 91.0 µg/ml) and two nematode inoculation conditions (presence or absence) were evaluated in a six-week growth chamber experiments. Results from this study showed that a single root application of the
-CA + PPA mixture significantly reduced the penetration of
infective juveniles (J2s) into the cowpea roots. The potential toxicity of
-CA + PPA on RKN-susceptible cowpea seedlings was also investigated. The effect of
-CA + PPA x nematode inoculation interactions and the
-CA + PPA mixture did not show significant phytotoxic effects, nor adversely affected plant growth parameters or altered leaf chlorophyll content. Total leaf chlorophyll and chlorophyll
content were significantly reduced (by 15% and 22%, respectively) only by the nematode inoculum, not by any of the SM treatments. Our results suggest that a single root application of a mixture of
-CA and PPA reduces
J2's ability to infect the roots without impairing plant growth or chlorophyll content.
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•X. bovieni jollieti strainT6SS clusters play a role in nematodes colonization and reproduction.•vgrG and hcp genes are required to fully colonize the nematode host.•vgrG genes are ...not required for biofilm but play a role in outcompeting other Xenorhabdus bacteria.•hcp and vgrG genes are needed to support the reproductive fitness of the nematodes.
Xenorhabdus, like other Gram-negative bacteria, possesses a Type 6 Secretion System (T6SS) which acts as a contact-dependent molecular syringe, delivering diverse proteins (effectors) directly into other cells. The number of T6SS loci encoded in Xenorhabdus genomes are variable both at the inter and intraspecific level. Some environmental isolates of Xenorhabdus bovienii, encode at least one T6SS locus while others possess two loci. Previous work conducted by our team demonstrated that X. bovienii Jollieti strain SS-2004, which has two T6SSs (T6SS-1 and T6SS-2), hcp genes are required for biofilm formation. Additionally, while T6SS-1 hcp gene plays a role in the antibacterial competition, T6SS-2 hcp does not. In this study, we tested the hypothesis that vgrG genes are also involved in mutualistic and pathogenic interactions. For this purpose, targeted mutagenesis together with wet lab experiments including colonization, competition, biofilm, and virulence experiments, were carried out to assess the role of vgrG in the mutualistic and antagonistic interactions in the life cycle of XBJ. Our results revealed that vgrG genes are not required for biofilm formation but play a role in outcompeting other Xenorhabdus bacteria. Additionally, both vgrG and hcp genes are required to fully colonize the nematode host. We also demonstrated that hcp and vgrG genes in both T6SS clusters are needed to support the reproductive fitness of the nematodes. Overall, results from this study revealed that in X. bovieni jollieti strain, the twoT6SS clusters play an important role in the fitness of the nematodes in relation to colonization and reproduction. These results lay a foundation for further investigations on the functional significance of T6SSs in the mutualistic and pathogenic lifecycle of Xenorhabdus spp.
...symbiont heritability has not been demonstrated, and the nature of C. briggsae's bacterial association remains unresolved 10, 11, 39. Because C. briggsae has not met the suggested criteria, it ...should not be considered an EPN, facultative or otherwise, until heritability of the pathogenic bacteria is demonstrated and more is known about bacterial release and speed of host death. ...these taxa should be considered EPNs even though further research is required to determine the nature and heritability of their bacterial associations, and whether they are obligate or facultative EPNs.
Gram-negative
bacteria have a dual lifestyle: they are mutualists of
nematodes and are pathogens of insects. Together, this nematode–bacterium partnership has been used to successfully control a wide ...range of agricultural insect pests.
produce a diverse array of small molecules that play key biological roles in regulating their dual roles. In particular, several secondary metabolites (SM) produced by this bacterium are known to play a critical role in the maintenance of a monoxenic infection in the insect host and are also known to prevent contamination of the cadaver from soil microbes and/or predation by arthropods. A few of the SM this bacteria produce have been isolated and identified, and their biological activities have also been tested in laboratory assays. Over the past two decades, analyses of the genomes of several
spp. have revealed the presence of SM numerous gene clusters that comprise more than 6% of these bacteria genomes. Furthermore, genome mining and characterization of biosynthetic pathways, have uncovered the richness of these compounds, which are predicted to vary across different
spp. and strains. Although progress has been made in the identification and function of SM genes and gene clusters, the targeted testing for the bioactivity of molecules has been scarce or mostly focused on medical applications. In this review, we summarize the current knowledge of
SM, emphasizing on their activity against plant pathogens and parasites. We further discuss their potential in the management of agricultural pests and the steps that need to be taken for the implementation of
SM in pest management.
Entomopathogenic nematodes of the genus
have a mutualistic relationship with bacteria of the genus
and together they form an antagonist partnership against their insect hosts. The nematodes ...(third-stage infective juveniles, or IJs) protect the bacteria from the external environmental stressors and vector them from one insect host to another.
produce secondary metabolites and antimicrobial compounds inside the insect that protect the cadaver from soil saprobes and scavengers. The bacteria also become the nematodes' food, allowing them to grow and reproduce. Despite these benefits, it is yet unclear what the potential metabolic costs for
IJs are relative to the maintenance and vectoring of
. In this study, we performed a comparative dual RNA-seq analysis of IJs of two nematode-bacteria partnerships:
-
and
-
. For each association, three conditions were studied: (1) IJs reared in the insect (
colonized), (2) colonized IJs reared on liver-kidney agar (
colonized), and (3) IJs depleted by the bacteria reared on liver-kidney agar (
aposymbiotic). Our study revealed the downregulation of numerous genes involved in metabolism pathways, such as carbohydrate, amino acid, and lipid metabolism when IJs were reared
, both colonized and without the symbiont. This downregulation appears to impact the longevity pathway, with the involvement of glycogen and trehalose metabolism, as well as arginine metabolism. Additionally, a differential expression of the venom protein known to be secreted by the nematodes was observed when both
species were depleted of their symbiotic partners. These results suggest
IJs may have a mechanism to adapt their virulence in absence of their symbionts.
Many Gram-negative bacteria have evolved insect pathogenic lifestyles. In all cases, the ability to cause disease in insects involves specific bacterial proteins exported either to the surface, the ...extracellular environment, or the cytoplasm of the host cell. They also have several distinct mechanisms for secreting such proteins. In this review, we summarize the major protein secretion systems and discuss examples of secreted proteins that contribute to the virulence of a variety of Gram-negative entomopathogenic bacteria, including
,
,
,
, and
species. We also briefly summarize two classes of exported protein complexes, the PVC-like elements, and the Tc toxin complexes that were first described in entomopathogenic bacteria.
Parasitism is a major ecological niche for a variety of nematodes. Multiple nematode lineages have specialized as pathogens, including deadly parasites of insects that are used in biological control. ...We have sequenced and analyzed the draft genomes and transcriptomes of the entomopathogenic nematode Steinernema carpocapsae and four congeners (S. scapterisci, S. monticolum, S. feltiae, and S. glaseri).
We used these genomes to establish phylogenetic relationships, explore gene conservation across species, and identify genes uniquely expanded in insect parasites. Protein domain analysis in Steinernema revealed a striking expansion of numerous putative parasitism genes, including certain protease and protease inhibitor families, as well as fatty acid- and retinol-binding proteins. Stage-specific gene expression of some of these expanded families further supports the notion that they are involved in insect parasitism by Steinernema. We show that sets of novel conserved non-coding regulatory motifs are associated with orthologous genes in Steinernema and Caenorhabditis.
We have identified a set of expanded gene families that are likely to be involved in parasitism. We have also identified a set of non-coding motifs associated with groups of orthologous genes in Steinernema and Caenorhabditis involved in neurogenesis and embryonic development that are likely part of conserved protein-DNA relationships shared between these two genera.
Entomopathogenic
bacteria are endosymbionts of
nematodes and together they form an insecticidal mutualistic association that infects a wide range of insect species.
produce an arsenal of toxins and ...secondary metabolites that kill the insect host. In addition, they can induce the production of diverse phage particles. A few studies have focused on one integrated phage responsible for producing a phage tail-like bacteriocin, associated with an antimicrobial activity against other
species. However, very little is known about the diversity of prophage regions in
species.
In the present study, we identified several prophage regions in the genome of
AN6/1. We performed a preliminary study on the relative expression of genes in these prophage regions. We also investigated some genes (not contained in prophage region) known to be involved in SOS bacterial response (
and
) associated with mitomycin C and UV exposure.
We described two integrated prophage regions (designated Xnp3 and Xnp4) not previously described in the genome of
AN6/1. The Xnp3 prophage region appears very similar to complete Mu-like bacteriophage. These prophages regions are not unique to
species, although they appear less conserved among
species when compared to the previously described p1 prophage region. Our results showed that mitomycin C exposure induced an up-regulation of
and
suggesting activation of SOS response. In addition, mitomycin C and UV exposure seems to lead to up-regulation of genes in three of the four integrated prophages regions.
Beauveria bassiana is a facultative entomopathogen with an extremely broad host range that is used as a commercial biopesticide for the control of insects of agricultural, veterinary and medical ...significance.
B. bassiana produces bassianolide, a cyclooligomer depsipeptide secondary metabolite. We have cloned the
bbBsls gene of
B. bassiana encoding a nonribosomal peptide synthetase (NRPS). Targeted inactivation of the
B. bassiana genomic copy of
bbBsls abolished bassianolide production, but did not affect the biosynthesis of beauvericin, another cyclodepsipeptide produced by the strain. Comparative sequence analysis of the BbBSLS bassianolide synthetase revealed enzymatic domains for the iterative synthesis of an enzyme-bound dipeptidol monomer intermediate from
d-2-hydroxyisovalerate and
l-leucine. Further BbBSLS domains are predicted to catalyze the formation of the cyclic tetrameric ester bassianolide by recursive condensations of this monomer. Comparative infection assays against three selected insect hosts established bassianolide as a highly significant virulence factor of
B. bassiana.
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