When mutualists are pathogens: an experimental study of the symbioses between Steinernema (entomopathogenic nematodes) and Xenorhabdus (bacteria) (original) (raw)
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BMC evolutionary biology, 2006
Symbioses between invertebrates and prokaryotes are biological systems of particular interest in order to study the evolution of mutualism. The symbioses between the entomopathogenic nematodes Steinernema and their bacterial symbiont Xenorhabdus are very tractable model systems. Previous studies demonstrated (i) a highly specialized relationship between each strain of nematodes and its naturally associated bacterial strain and (ii) that mutualism plays a role in several important life history traits of each partner such as access to insect host resources, dispersal and protection against various biotic and abiotic factors. The goal of the present study was to address the question of the impact of Xenorhabdus symbionts on the progression and outcome of interspecific competition between individuals belonging to different Steinernema species. For this, we monitored experimental interspecific competition between (i) two nematode species: S. carpocapsae and S. scapterisci and (ii) their ...
Journal of Crop Protection, 2017
By conducting three different methods, we report on the isolation of five novel strains of non-symbiotic bacteria from crushed infective juveniles (IJs) of four species of entomopathogenic nematodes (EPN) including Heterorhabditis bacteriophora, Steinernema carpocapsae, Steinernema feltiae, and Steinernema glaseri and five bacterial species from hemolymph of insect larvae infected with EPNs. Samples of hemolymph of infected Galleria mellonella L. larvae by EPNs and crushed surface sterilized IJs were bulk streaked onto both MacConkey and NBTA agar. To further ensure diagnoses, extracted DNA from IJs bulk was subjected to PCR by 16S-rRNA bacterial universal primers. Bacteria were identified using biochemical and phylogenetic analysis. Based on 16S-rRNA gene sequence, maximum parsimony, maximum likelihood and neighbour joining phylogenetic analyses were conducted, as well as comparisons of predicted RNA secondary structures. Four species of bacteria were identified including: Stenotro...
Systematic Parasitology, 2010
Nematodes of the genus Steinernema Travassos, 1927 (Nematoda: Steinernematidae) and their associated bacteria, Xenorhabdus spp. (gamma-Proteobacteria), are an emergent model of terrestrial animal-microbe symbiosis. Interest in this association initially arose out of their potential as biocontrol agents against insect pests, but, despite advances in their field application and the growing popularity of this model system, relatively little has been published to uncover the evolutionary facets of this beneficial partnership. This study adds to the body of knowledge regarding nematode-bacteria symbiosis by proposing a possible scenario for their historical association in the form of a cophylogenetic hypothesis. Topological and likelihood based testing methods were employed to reconstruct a history of association between 30 host-symbiont pairs and to gauge the level of similarity between their inferred phylogenetic patterns.
Journal of Invertebrate Pathology, 2010
Xenorhabdus spp., are gram-negative bacterial symbionts of entomopathogenic nematodes in the genus Steinernema. A specialized and intimate relationship exists between nematode and bacteria, affecting many of their life history traits, such as nutrition, dispersal, host-finding, foraging and defense from biotic and abiotic factors. Xenorhabdus currently comprises more than 20 species isolated from Steinernema spp. with diverse host range, host foraging behavior, reproductive modes and environmental tolerance. Xenorhabdus phylogenies have historically been based on 16s rDNA sequence analyses, and only recently has data from housekeeping genes been employed. The prevalence of lateral gene transfer among bacteria calls for a wider perspective when considering their phylogeny. With the increasing number of Xenorhabdus species and strains, various perspectives need to be considered for investigating the evolutionary history of these nematode bacterial symbionts, In this study, we reconstruct the evolutionary histories of 30 species of Xenorhabdus considering the traditional 16s rDNA gene region as well as the housekeeping genes recA and serC. Datasets were analyzed individually and then combined, using a variety of phylogenetic criteria.
Entomopathogenic symbiotic bacteria, Xenorhabdus and Photorhabdus of nematodes
World Journal of Microbiology & Biotechnology, 2001
Xenorhabdus and Photorhabdus species are entomopathogenic bacteria with a wide insect host range, that belong to the family Enterobacteriaceae. Xenorhabdus and Photorhabdus species symbiotically associate with nematodes of the families Steinernematidae and Heterorhabditidae respectively. The factor(s) determining the symbiotic interaction between nematodes and bacteria are yet to be identified. Xenorhabdus and Photorhabdus species exist in two main phenotypic forms, a phenomenon known as phase variation. The phase I (or primary form) varies from phase II (or secondary form) in certain physiological and morphological characteristics. There is no variation in the DNA integrity of phase I and phase II and this supports epigenetic regulatory mechanism in phase variation. Certain pathogenic determinants such as pili, lipopolysaccharides and toxins contribute to the pathogenicity of Xenorhabdus and Photorhabdus species, and both appear to be equally pathogenic to insects. The observed similarity in their virulence to insect hosts may reflect possible in vivo conversion of phase II to phase I, however the host cellular invasion and virulence is yet to be properly understood. The virulence of Xenorhabdus variants varies among insects apparently due to factors which include the feeding habits of the insects. The molecular mechanism and biological significance of phase variation are presently unknown.
Abstracts of NEMASYM: The Second Nematode-Bacteria Symbioses Research Coordination Network Meeting
Intimate associations between microbes and eukaryotes are widespread in nature, occurring in every type of ecological niche. The spectrum of such interactions ranges from highly integrated obligatory symbioses to 'loose' associations. Microbial symbioses are integral to the function of every ecosystem on Earth. Therefore to gain insights into fundamental processes underlying symbiosis and the role of symbiosis in earth/human ecosystems, researchers in this project have focused on one of the most common eukaryote-prokaryote interactions: that between nematodes and bacteria. Associations between nematodes and bacteria range from fortuitous to obligate and from beneficial to pathogenic. The ubiquity and diversity of nematode-bacterium symbioses make them an excellent model to understand the key questions in symbiosis. However, while numerous researchers worldwide are currently studying associations between these two groups of organisms, these scientists rarely interact because their field of research is often defined by the organism studied rather than by the process (in this case, symbiosis). To reddress this critical need for crossing disciplinary lines, a Research Coordination Network on 'Nematode-Bacteria Symbioses' (NEMASYM) was established in 2008 to promote the intellectual discourse among scientists studying bacteria-nematode associations. This network is funded by the National Science Foundation and its specific goals of are: 1) Foster interdisciplinary collaborations between scientists; 2) Encourage scientists engaged in basic and applied research to explore how cross-talk and networking can enhance and advance science in this field; and 3) Develop and distribute educational materials to scientists and educators to promote the study of nematode-bacteria symbioses as model systems in science and education.
BMC evolutionary biology, 2017
The entomopathogenic nematode Steinernema carpocapsae has been used worldwide as a biocontrol agent for insect pests, making it an interesting model for understanding parasite-host interactions. Two models propose that these interactions are co-evolutionary processes in such a way that equilibrium is never reached. In one model, known as "arms race", new alleles in relevant genes are fixed in both host and pathogens by directional positive selection, producing recurrent and alternating selective sweeps. In the other model, known as"trench warfare", persistent dynamic fluctuations in allele frequencies are sustained by balancing selection. There are some examples of genes evolving according to both models, however, it is not clear to what extent these interactions might alter genome-level evolutionary patterns and intraspecific diversity. Here we investigate some of these aspects by studying genomic variation in S. carpocapsae and other pathogenic and free-living ...
Archives of Microbiology, 2018
Three strains of symbiotic bacteria were isolated from an entomopathogenic nematode Steinernema poinari retrieved from soil in eastern Poland. Using 16S rDNA, recA, gltX, gyrB, and dnaN gene sequences for phylogenetic analysis, these strains were shown to belong to the species Xenorhabdus bovienii. The nucleotide identity between the studied S. poinari microsymbionts and other X. bovienii strains calculated for 16S rDNA and concatenated sequences of four protein-coding genes was 98.7-100% and 97.9-99.5%, respectively. The phenotypic properties of the isolates also supported their close phylogenetic relationship with X. bovienii. All three tested X. bovienii strains of different Steinernema clade origin supported the recovery of infective juveniles and subsequent development of the nematode population. However, the colonization degree of new infective juvenile generations was significantly affected by the bacterial host donor/recipient. The colonization degree of infective juveniles reared on bacterial symbionts deriving from a non-cognate clade of nematodes was extremely low, but proved the possible host-switching between non-related Steinernema species.
Special Issue: Insects, Nematodes, and Their Symbiotic Bacteria
Insects, 2020
This special issue contains articles that add to the ever-expanding toolbox of insect pathogenic nematodes (entomopathogenic nematodes; EPNs) as well articles that provide new insights into the mutualistic interaction between EPNs and their hosts. The study of natural infection models such as EPNs allows detailed insight into micro- and macro-evolutionary dynamics of innate immune reactions, including known but also emerging branches of innate immunity. Additional new insights into the kinetics of EPN infections are gained by increased spatiotemporal resolution of advanced transcriptome studies and live imaging.