Metatranscriptomic Analysis of the Mouse Gut Microbiome Response to the Persistent Organic Pollutant 2,3,7,8-Tetrachlorodibenzofuran

Abstract

Persistent organic pollutants (POPs) are important environmental chemicals and continued study of their mechanism of action remains a high priority.POPs, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), and polychlorinated biphenyls (PCBs), are widespread environmental contaminants that are agonists for the aryl hydrocarbon receptor (AHR). Activation of the AHR modulates the gut microbiome community structure and function, host immunity, and the host metabolome. In the current study, male C57BL6/J mice were exposed, via the diet, to 5 µg/kg body weight (BW) TCDF or 24 µg/kg BW of TCDF every day for 5 days. The functional and structural changes imparted by TCDF exposure to the gut microbiome and host metabolome were explored via 16S rRNA gene amplicon sequencing, metabolomics, and bacterial metatranscriptomics. Significant changes included increases in lipopolysaccharide (LPS) biosynthesis gene expression after exposure to 24 µg/kg BW of TCDF. Increases in LPS biosynthesis were confirmed with metabolomics and LPS assays using serum obtained from TCDF-treated mice. Significant increases in gene expression within aspartate and glutamate metabolism were noted after exposure to 24 µg/kg BW of TCDF. Together, these results suggest that after exposure to 24 µg/kg BW of TCDF, the gut microbiome increases the production of LPS and glutamate to promote localized gut inflammation, potentially using glutamate as a stress response.

Metabolic impact of persistent organic pollutants on gut microbiota

“…We identified general transcriptional responses to most POPs related to energy metabolism pathways including the TCA cycle, butyrate metabolism, and pyruvate metabolism, supported by our metabolomics data. Similar observations have been reported in a previous mouse study 20 and an in vitro study that reported a dose-dependent inhibitory effect and a disruption in bacterial fermentation processes by PCB 126 exposure using a mouse fecal culture. 36 The direct in vitro effects may translate into microbiome shifts in vivo, which contribute to the disruption of glucose tolerance in host with POPs exposure.…”

“…Another prominent finding in this study was the integrated and detailed characterization of the altered metabolic pathways using metatranscriptomics data combined with metabolomics data. Oral POP treatment modulated the microbial community, 13,20 which was not fully consistent with what we observed in the in vitro study. The differences could be due to intervention duration and/or the lack of host-mediated processes in in vitro systems.…”

“…40 It will be interesting to see whether POPs cause varied responses in protein transport to Grampositive and Gram-positive bacteria in the future work. Notably, our results also emphasized many distinct transcriptional responses of PCB 153 on the cecal bacteria, including the induction of bacterial membrane biogenesis, 41 stress response pathways, 20 and defense of DNA damage. 42 Exposure to (non-coplanar) PCB-153 resulted in a more dramatic metabolic and transcriptional response to bacteria relative to (coplanar) PCB-126.…”

“…10,12,18 Mounting laboratory animal studies report that POP exposure might alter the microbial community structure and/or the metabolic activities, leading to host disorders. 13,20,29 In this study, we investigated the direct impact of four POPs on the gut microbiota at the physiological, metabolic, and transcriptional levels using in vitro systems. The four POPs used in this work: (i) TCDF, considerable shorter half-life in rodents; 13 (ii) TCDD, the most potent aryl hydrocarbon receptor agonist; 30 and (iii) two PCBs (coplanar PCB 126 and noncoplanar PCB 153), are known to have a different degree of toxicity.…”

“…13,19 Moreover, our lab investigated the functional and structural changes imparted by dietary TCDF to the gut microbiota and host using 16S rRNA gene sequencing, metabolomics, and bacterial metatranscriptomics. 20 However, most studies to date have assessed host toxicity, while the direct effect of POPs on the gut microbiota have been explored by relatively few studies. Here, we combined flow cytometry, 16S rRNA gene sequencing, metatranscriptomics, and metabolomics to determine the responses of the gut microbiome to four POPs including TCDF, TCDD, and two PCBs (Figure 1).…”