Gut microbial populations influence immune homeostasis and are associated with a number of diseases including obesity, diabetes, inflammation and inflammatory bowel disease. A review of the current literature reveals that both gut microbiota and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) influence immune responses and host diseases. Clostridia species, Bacteroides and segmented filamentous bacteria (SFB) are important members of the intestinal microbial population that participate towards initiating immune responses and maintaining immune homeostasis. Exposure to the environmental contaminant, TCDD is associated with disruption of immune balance and immunosuppression in the host. Although several studies have pinpointed the effect of both TCDD and gut microbiota separately on host health and diseases, little or no research has been done to study their interaction with each other. Knowledge of the impact of TCDD exposure on key intestinal microbial members is important to understand their role in immune regulation and metabolic disorders. The aim of this study is to investigate the changes in abundance of specific gut microbial populations including SFB, Bacteroides, Clostridium cluster IV, Clostridium cluster XIVa, Lactobacillus and their functional genes with exposure to TCDD. Fecal samples taken from mice exposed to varying doses of TCDD over 12, 30 and 90-day time periods were analyzed using qPCR assays targeting these key microorganisms or their functional groups. The abundance of both 16S rRNA gene and flagellin gene of intestinal SFB increases with exposure to TCDD in a dose-dependent manner, with up to 10-fold increase in SFB observed in mice exposed to 1-30 μg/kg TCDD. A relative decrease in abundance of members of Clostridium IV and XIVa, and Bacteroides is found in TCDD-dosed mice groups in the short term high dose study. This work determined that TCDD exposure influences changes in abundance within key members of the intestinal microbial population, retarding healthy commensalism and thereby allowing overgrowth of pathobionts. Therefore, specific members of the gut microbial population may influence host immunity and metabolism in hosts affected by environmental toxicants such as TCDD. This work highlights that TCDD is responsible for microbial dysbiosis in the mice intestinal tract; this dysbiosis might be partially responsible for TCDD-related diseases including diabetes, inflammatory bowel disease, and autoimmune diseases observed in humans.
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