The Effects of Variation in Electron Donor Concentration and Type on Deep-Sea Endosymbiont Community Composition and Gene Expression

Chemosynthetic symbioses are among the most prevalent microbial symbioses found in marine systems. These associations often dominate reducing environments such as hydrothermal vents, where they play critical roles in biogeochemical cycling. Among the diverse number of organisms that participate in chemosynthetic symbioses is Ifremeria nautilei, a gastropod found surrounding the deep-sea hydrothermal vents of the South Pacific Ocean. Little is known about how chemosynthetic symbiont community composition and gene expression change in response to gradients of electron donors in the vent environment. Understanding these changes offers significant insight into the environmental conditions and physiological mechanisms necessary to sustain the relationship present between host and symbiont. To address this question, individual Ifremeria were collected from the Lau Basin hydrothermal vent system and placed in pressurized, sterile aquaria under the following conditions: i) no electron donor, ii) 100 µM hydrogen sulfide, iii) 300 µM hydrogen sulfide, iv) 300 µM thiosulfate. Stable carbon isotope (13C) incorporation rates were determined for each condition, with 300 µM thiosulfate yielding the highest average rate of carbon incorporation. Amplicon (16S rRNA gene) and metatranscriptomic sequencing were used to compare the phylogenetic diversity and differential gene expression of the symbiotic communities in gill tissue excised from Ifremeriain each treatment. Amplicon analyses revealed two major symbiont lineages within the phylum γ-proteobacteria: putative sulfur-oxidizing symbionts of the Chromatiales and methane-oxidizing symbionts of the Methylococcales. Of these, Chromatiales symbionts dominated, consisting of a single operational taxonomic unit (OTU) representing 81.2-99.6% of the symbiont population. Methylococcales symbionts were represented by two distinct OTUs (0.003-17.5% of sequences) and were present in all host individuals, excluding those exposed to 300uM hydrogen. Preliminary results of the metatranscriptome analysis confirm the expression of genes from both symbiont pools, including genes mediating sulfur oxidation and methane oxidation, despite an assumed lack of methane in the treatments. Genes for sulfur oxidation were ten-fold higher in abundance than those for methane oxidation. These results confirm that Ifremeria engages in a "dual" symbiont strategy using thiotrophic and methanotrophic partners and that this community may be sensitive to changes in electron donor availability, due potentially to symbiont competition within the host, host sanctions of symbiont "cheaters," or direct effects of substrate (sulfide) toxicity.Undergraduat

Interview with Dana Burns

Fall 2010 English 1101 assignment for Dr. Kathryn Crowther.Interview with Mr. Dana Burns, an executive director for Coca-Cola Headquarters in Atlanta

Metatranscriptional Response of Chemoautotrophic Ifremeria nautilei Endosymbionts to Differing Sulfur Regimes

Endosymbioses between animals and chemoautotrophic bacteria are ubiquitous at hydrothermal vents. These environments are distinguished by high physico-chemical variability, yet we know little about how these symbioses respond to environmental fluctuations. We therefore examined how the γ-proteobacterial symbionts of the vent snail Ifremeria nautilei respond to changes in sulfur geochemistry. Via shipboard high-pressure incubations, we subjected snails to 105 μM hydrogen sulfide (LS), 350 μM hydrogen sulfide (HS), 300 μM thiosulfate (TS) and seawater without any added inorganic electron donor (ND). While transcript levels of sulfur oxidation genes were largely consistent across treatments, HS and TS treatments stimulated genes for denitrification, nitrogen assimilation, and CO2 fixation, coincident with previously reported enhanced rates of inorganic carbon incorporation and sulfur oxidation in these treatments. Transcripts for genes mediating oxidative damage were enriched in the ND and LS treatments, potentially due to a reduction in O2 scavenging when electron donors were scarce. Oxidative TCA cycle gene transcripts were also more abundant in ND and LS treatments, suggesting that I. nautilei symbionts may be mixotrophic when inorganic electron donors are limiting. These data reveal the extent to which I. nautilei symbionts respond to changes in sulfur concentration and species, and, interpreted alongside coupled biochemical metabolic rates, identify gene targets whose expression patterns may be predictive of holobiont physiology in environmental samples

Investigation of Genetic Susceptibility to Blastomycosis Reveals Interleukin-6 as a Potential Susceptibility Locus

Blastomycosis is a potentially life-threatening infection caused by the fungus Blastomyces dermatitidis. As with related fungal diseases, blastomycosis is noted to affect some populations more than others. These patterns of illness are often not related to predisposing conditions or exposure risks; thus, genetic differences are thought to underlie these health disparities. People of Hmong ancestry in Wisconsin are at elevated risk of blastomycosis compared to the general population. We studied the genetic codes of Hmong blastomycosis patients and identified candidate sites in their genomes that may explain their susceptibility to this infection. We further studied one particular region of the genome that is involved with the immune processes that fight B. dermatitidis. Our work revealed population differences in the response to fungi. A better understanding of the genetic underpinnings of susceptibility to infectious diseases has broader implications for community health, especially in the paradigm of personalized medicine.Genetic differences are hypothesized to underlie ethnic disparities in incidence rates of the endemic systemic mycoses, including blastomycosis. Individuals of Hmong ancestry display elevated risk for this serious fungal infection. Here, we interrogated the genomes of Wisconsin (WI) Hmong blastomycosis patients using homozygosity mapping to uncover regions of the genome that are likely shared among the greater Hmong population and filtered for variants with high potential to affect disease susceptibility. This approach uncovered 113 candidate susceptibility variants, and among the most promising are those in genes involved in the interleukin-17 (IL-17) response. In particular, we identified 25 linked variants near the gene encoding IL-6 (IL6). We validated differences in cytokine production between Hmong and European volunteers and formally demonstrated a critical role for IL-6 in the development of adaptive immunity to Blastomyces dermatitidis. Our findings suggest that the dysregulation of IL-17 responses underlies a recently reported and poorly understood ethnic health disparity