Phase Variation in Xenorhabdus nematophilus and Photorhabdus luminescens: Differences in Respiratory Activity and Membrane Energization (original) (raw)
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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.
Phase Variation in Xenorhabdus nematophilus
1998
Xenorhabdus nematophilus is a symbiotic bacterium that inhabits the intestine of entomopathogenic nema- todes. The bacterium-nematode symbiotic pair is pathogenic for larval-stage insects. The phase I cell type is the form of the bacterium normally associated with the nematode. A variant cell type, referred to as phase II, can form spontaneously under stationary-phase conditions. Phase II cells do not elaborate
ISRN Microbiology, 2014
Xenorhabdus nematophila, an entomopathogenic bacterium that symbiotically associates with the entomoparasitic nematodeSteinernema carpocapsae, was studied to determine its physiological parameters of glucose utilization.X. nematophilawas cultured in chemically defined media containing various concentrations of glucose under optimal conditions utilizing a two-liter fermentation system. Specific growth rates were obtained from each glucose batch. Specific growth rates and their associated glucose concentrations were used to determine physiological parameters. These parameters include the bacterium’s substrate utilization constant (Ks) and its maximum specific growth rate (μmax). The bacteria exhibited aKsvalue of 2.02 mg/L suggesting thatX. nematophilahas a high affinity for glucose. TheμmaxofXenorhabduswas determined to be 1.03 h−1. Further research is needed to determine if microbial affinities to different substrates have any influence on biological relationships (symbiosis, pathog...
Role of Mrx Fimbriae of Xenorhabdus nematophila in Competitive Colonization of the Nematode Host
Applied and Environmental Microbiology, 2011
ABSTRACTXenorhabdus nematophilaengages in mutualistic associations with the infective juvenile (IJ) stage of specific entomopathogenic nematodes. Mannose-resistant (Mrx) chaperone-usher-type fimbriae are produced when the bacteria are grown on nutrient broth agar (NB agar). The role of Mrx fimbriae in the colonization of the nematode host has remained unresolved. We show thatX. nematophilagrown on LB agar produced flagella rather than fimbriae. IJs propagated onX. nematophilagrown on LB agar were colonized to the same extent as those propagated on NB agar. Further, progeny IJs were normally colonized bymrxmutant strains that lacked fimbriae both when bacteria were grown on NB agar and when coinjected into the insect host with aposymbiotic nematodes. Themrxstrains were not competitively defective for colonization when grown in the presence of wild-type cells on NB agar. In addition, a phenotypic variant strain that lacked fimbriae colonized as well as the wild-type strain. In contras...
Swarming and Swimming Changes Concomitant with Phase Variation in Xenorhabdus nematophilus
Applied and Environmental Microbiology, 1995
Xenorhabdus spp., entomopathogenic bacteria symbiotically associated with nematodes of the family Steinernematidae, occur spontaneously in two phases. Phase I, the variant naturally isolated from the infective-stage nematode, provides better conditions than the phase II variant for nematode reproduction. This study has shown that Xenorhabdus phase I variants displayed a swarming motility when they were grown on a suitable solid medium (0.6 to 1.2% agar). Whereas most of the phase I variants from different Xenorhabdus spp. were able to undergo cycle of rapid and coordinately population migration over the surface, phase II variants were unable to swarm and even to swim in semisolid agar, particularly in X. nematophilus. Optical and electron microscopic observations showed nonmotile cells with phase II variants of X. nematophilus F1 which lost their flagella. Flagellar filaments from strain F1 phase I variants were purified, and the molecular mass of the flagellar structural subunit was estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to be 36.5 kDa. Flagellin from cellular extracts or culture medium of phase II was undetectable with antiserum against the denatured flagellin by immunoblotting analysis. This suggests that the lack of flagella in phase II cells is due to a defect during flagellin synthesis. The importance of such a difference of motility between both phases is discussed in regard to adaptation of these bacteria to the insect prey and the nematode host.
Research Square (Research Square), 2024
This study provides an analysis of two isolates of entomopathogenic nematodes and their symbiotic bacteria recovered from soil samples of northwest of Iran. Molecular techniques, including phylogenetic analysis of ITS-rDNA, 28s-rDNA, 16s-rDNA and gyrB sequences identi ed nematodes as Heterorhabditis bacteriophora and Steinernema carpocapsae, along with their symbiotic bacteria Photorhabdus thracensis and Xenorhabdus nematophila, respectively. The growth dynamics of these bacteria were also explored, revealing similar growth curves and distinctive patterns. Xenorhabdus nematophila displayed a rapid transition into the log and stationary phases, differing from P. thracensis. Within 32 hours post-inoculation, both bacteria experienced growth reduction, but P. thracensis demonstrated a steeper decrease. Moreover, the study assessed the virulence of the bacteria against Galleria mellonella larvae, highlighting higher virulence of X. nematophila (LC50 = 294.36 × 10 6). Additionally, we explored the inhibitory effect of antibiotics, with Ampicillin and Chloramphenicol identi ed as the most effective against P. thracensis and X. nematophila, respectively. The inhibitory effect of antimicrobial agents on the growth of P. thracensis and X. nematophila was concentration-dependent, highlighting the importance of selecting appropriate concentrations for effective control of bacterial infections while minimizing disruption to bene cial symbiotic bacteria during mass production process of bacteria or entomopathogenic nematodes. Among the antibiotics with the lowest inhibitory effects on bacteria, Erfamicin caused lowest mortality on infective juveniles of both nematodes.
Applied and Environmental Microbiology, 2008
Many animals and plants have symbiotic relationships with beneficial bacteria. Experimentally tractable models are necessary to understand the processes involved in the selective transmission of symbiotic bacteria. One such model is the transmission of the insect-pathogenic bacterial symbionts Photorhabdus spp. by Heterorhabditis bacteriophora infective juvenile (IJ)-stage nematodes. By observing egg-laying behavior and IJ development, it was determined that IJs develop exclusively via intrauterine hatching and matricide (i.e., endotokia matricida). By transiently exposing nematodes to fluorescently labeled symbionts, it was determined that symbionts infect the maternal intestine as a biofilm and then invade and breach the rectal gland epithelium, becoming available to the IJ offspring developing in the pseudocoelom. Cell-and stage-specific infection occurs again in the pre-IJ pharyngeal intestinal valve cells, which helps symbionts to persist as IJs develop and move to a new host. Synchronous with nematode development are changes in symbiont and host behavior (e.g., adherence versus invasion). Thus, Photorhabdus symbionts are maternally transmitted by an elaborate infectious process involving multiple selective steps in order to achieve symbiont-specific transmission.
2012
Four entomopathogenic bacterial isolates of Photorhabdus luminescens designated as A, C, D, and E were separately obtained from the haemolymph of Galleria melonella infected with the corresponding indigenous nematode isolates of Heterorhabditis bacteriofora and the fifth P. luminescens akhurstii B from Egyptian H. indica isolate B. The effect of metabolite concentration for each of these bacterial isolates and some physical parameters (i.e., temperature, pH, and sodium chloride) on the metabolite-induced mortality for G. mellonella larvae as well as the magnitude of the bacterial growth under different concentrations of NaCl and pH values was investigated. This mortality differed (P ≤ 0.05) among the tested isolates at the assigned ranges of these physical parameters. The cell-free filtrates of 4 x 10 cells/ml broth of the bacterium P. luminescens akhurstii isolate B could induce 100% insect mortality after one day of exposure, showing the highest virulence against G. mellonella lar...