Project description:We exposed two groups of green frog tadpoles that differed in their microbiome composition to heat stress or control conditions. We subsequently used RNAseq to profile gene expression in their gut to understand how the microbiome impacts host responses to heat.
Project description:Abstract: Natural communities of microbes inhabiting amphibian skin, the skin microbiome, are critical to supporting amphibian health and disease resistance. To enable the pro-active health assessment and management of amphibians on Army installations and beyond, we investigated the effects of acute (96h) munitions exposures to Rana pipiens (leopard frog) tadpoles and the associated skin microbiome, integrated with RNAseq-based transcriptomic responses in the tadpole host. Tadpoles were exposed to the legacy munition 2,4,6-trinitrotoluene (TNT), the new insensitive munition (IM) formulation, IMX-101, and the IM constituents nitroguinidine (NQ) and 1-methyl-3-nitroguanidine (MeNQ). The 96h LC50 values and 95% confidence intervals were 2.6 (2.4, 2.8) for ΣTNT and 68.2 (62.9, 73.9) for IMX-101, respectively. The NQ and MeNQ exposures caused no significant impacts on survival in 96h exposures even at maximum exposure levels of 3,560 and 5,285 mg/L, respectively. However, NQ and MeNQ, as well as TNT and IMX-101 exposures, all elicited changes in the tadpole skin microbiome profile, as evidenced by significantly increased relative proportions of the Proteobacteria with increasing exposure concentrations, and significantly decreased alpha-diversity in the NQ exposure. The potential for direct and indirect effects of munitions exposures on the skin microbiome were observed. A direct effect of munitions on microbial flora included the observation of increased relative abundance of the munitions-tolerant, Aeromonadaceae and Pseudomonadaceae, in the NQ exposure. Potential indirect effects on the tadpole skin microbiome resulting from tadpole-host responses to munitions included transcriptional responses indicative of potential changes in skin mucus-layer properties as well as altered production of antimicrobial peptides and innate immune factors. Additional insights into the tadpole host’s transcriptional response to munitions exposures indicated that TNT and IMX-101 exposures each elicited significant enrichment of pathways involved in type-I and type-II xenobiotic metabolism mechanisms where dose-responsive increases in expression were observed. Significant enrichment and increased transcriptional expression of heme and iron binding functions in the TNT exposures was likely connected with known mechanisms of TNT toxicity including hemolytic anemia and methemoglobinemia. The significant enrichment and dose-responsive decrease in transcriptional expression of cell cycle pathways in the IMX-101 exposures was consistent with previous observations in fish, while significant enrichment of immune-related function in response to NQ exposure indicated potential immune suppression at the highest NQ exposure concentration. Finally, the MeNQ exposures elicited significantly decreased transcriptional expression of keratin 16, type I, a gene likely involved in keratinization processes in amphibian skin. Overall, munitions showed the potential to alter tadpole skin microbiome composition and affect transcriptional profiles in the amphibian host, some indicative of potentially impacted host health and immune status, each of which suggest potential implications for munitions exposure on disease susceptibility.
Project description:As part of the EcoToxChip project, 49 distinct exposure studies were conducted on three lab model species (Japanese quail, fathead minnow, African clawed frog) and three ecologically relevant species (double crested cormorant, rainbow trout, northern leopard frog), at multiple life stages (embryo, adult), exposed to eight chemicals of environmental concern (ethinyl estradiol-EE2, hexabromocyclododecane-HBCD, lead-Pb, selenomethionine-SeMe, 17β trenbolone-TB, chlorpyrifos-CPF, fluoxetine-FLX, and benzo [a] pyrene-BaP. Whole transcriptome analyses were conducted on these samples resulting in a rich RNA seq dataset covering various species, life stages and chemicals, which is one of the largest purposeful complications of RNA seq data within ecotoxicology. Recently, a unified bioinformatics platform of relevance to ecotoxicology, EcoOmicsAnalyst and ExpressAnalyst, was developed to facilitate RNA Seq analysis of non-model species lacking a reference transcriptome. The platform uses the Seq2Fun algorithm to map RNA-seq reads from eukaryotic species to an ortholog database comprised of protein sequences from >600 eukaryotic species (EcoOmicsDB) with a translated search. The availability of these tools presents a unique opportunity to examine the EcoToxChip RNA Seq dataset for cross species comparisons. This work shows the potential of the EcoOmicsAnalyst and Seq2Fun platform to facilitate fast and simple analysis of RNA Seq datasets from non-model organisms with unannotated genomes and conduct comparative transcriptomic analysis across various species and life stages for cross-species extrapolation.