Project description:Pasteuria spp. are endospore forming bacteria which act as natural antagonists to many of the most economically significant plant parasitic nematodes (PPNs). Highly species-specific nematode suppression may be observed in soils containing a sufficiently high density of Pasteuria spp. spores. This suppression is enacted by the bacteria via inhibition of root invasion and sterilization of the nematode host. Molecular methods for the detection of Pasteuria spp. from environmental DNA (eDNA) have been described; however, these methods are limited in both scale and in depth. We report the use of small subunit rRNA gene metabarcoding to profile Pasteuria spp. and nematode communities in parallel. We have investigated Pasteuria spp. population structure in Scottish soils using eDNA from two sources: soil extracted DNA from the second National Soil Inventory of Scotland (NSIS2); and nematode extracted DNA collected from farms in the East Scotland Farm Network (ESFN). We compared the Pasteuria spp. community culture to both nematode community structure and the physiochemical properties of soils. Our results indicate that Pasteuria spp. populations in Scottish soils are broadly dominated by two sequence variants. The first of these aligns with high identity to Pasteuria hartismeri, a species first described parasitizing Meloidogyne ardenensis, a nematode parasite of woody and perennial plants in northern Europe. The second aligns with a Pasteuria-like sequence which was first recovered from a farm near Edinburgh which was found to contain bacterial feeding nematodes and Pratylenchus spp. encumbered by Pasteuria spp. endospores. Further, soil carbon, moisture, bulk density, and pH showed a strong correlation with the Pasteuria spp. community composition. These results indicate that metabarcoding is appropriate for the sensitive, specific, and semi-quantitative profiling of Pasteuria species from eDNA.
Project description:Background: Gastrointestinal nematodes are a serious cause of morbidity and mortality in grazing ruminants. The major ovine defence mechanism is acquired immunity, which develops over time in response to infection. Nematode resistance varies both within and between breeds and is moderately heritable (h ~ 0.3). A detailed understanding of the genes and mechanisms involved in protective immunity, and the factors that regulate this response, is required to aid future breeding strategies as well as the development of effective and sustainable nematode control methods. The aim of this study was to compare the abomasal lymph node transcriptome of resistant and susceptible lambs in order to determine biological processes differentially expressed between resistant and susceptible lambs. Results: Scottish Blackface lambs, with divergent phenotypes for resistance, were challenged with 30,000 Teladorsagia circumcincta larvae (L3), and abomasal lymph node recovered at 7 and 14 days post-infection (dpi). High-throughput sequencing of abomasal lymph node cDNA was used to quantitatively sample the transcriptome with an average of 32 million reads per sample. A total of 194 and 144 genes were differentially expressed between resistant and susceptible lambs at 7 and 14 dpi respectively. Differentially expressed networks and biological processes were identified using Ingenuity Pathway Analysis. Resistant animals appear to generate a more rapid immune response as at 7 dpi processes relating to homing of lymphocytes, leukocyte migration and migration of antigen presenting cells were up-regulated. In susceptible animals this response appears to be delayed until approximately 14 dpi. Twenty-four Single Nucleotide Polymorphims (SNP), within 11 differentially expressed genes were tested for association with gastrointestinal nematode resistance in the Scottish Blackface lambs. Four SNPs in two genes (SLC30A2, and ALB) were suggestively associated with faecal egg count. Conclusions: A large number of genes were differentially expressed in the abomasal lymph node of resistant and susceptible lambs responding to gastrointestinal nematode challenge. Resistant Scottish Blackface lambs appear to generate a more rapid immune response to T. circumcincta. In susceptible lambs this response appears to be delayed until approximately 14 days post infection. SNP in two differentially expressed genes were suggestively associated with faecal egg count indicating that differentially expressed genes can be considered as candidate loci for mediating nematode resistance.
Project description:Pasteuria penetrans, an obligate endospore-forming parasite of Meloidogyne spp. (root knot nematodes), has been identified as a promising agent for biocontrol of these destructive agricultural crop pests. Pasteuria ramosa, an obligate parasite of water fleas (Daphnia spp.), has been shown to modulate cladoceran populations in natural ecosystems. Selected sporulation genes and an epitope associated with the spore envelope of these related species were compared. The sigE and spoIIAA/spoIIAB genes differentiate the two species to a greater extent than 16S rRNA and may serve as probes to differentiate the species. Single-nucleotide variations were observed in several conserved genes of five distinct populations of P. ramosa, and while most of these variations are silent single-nucleotide polymorphisms, a few result in conservative amino acid substitutions. A monoclonal antibody directed against an adhesin epitope present on P. penetrans P20 endospores, previously determined to be specific for Pasteuria spp. associated with several phytopathogenic nematodes, also detects an epitope associated with P. ramosa endospores. Immunoblotting provided patterns that differentiate P. ramosa from other Pasteuria spp. This monoclonal antibody thus provides a probe with which to detect and discriminate endospores of different Pasteuria spp. The presence of a shared adhesin epitope in two species with such ecologically distant hosts suggests that there is an ancient and ecologically significant recognition process in these endospore-forming bacilli that contributes to the virulence of both species in their respective hosts.