Characteristics of bacterial community and extracellular enzymes in response to atrazine application in black soil.

The ecological functioning of black soil largely depends on the activities of various groups of microorganisms. However, little is known about how atrazine, a widely used herbicide with known harmful effects on the environment, influences the microbial ecology of black soil, and the extracellular enzymes related to the carbon, nitrogen and phosphorus cycles. Here, we evaluated the change in extracellular enzymes and bacterial community characteristics in black soil after exposure to various concentrations of atrazine. Low concentrations of applied atrazine (10 - 20 mg kg-1) were almost completely degraded after 120 days. At high concentrations (80 - 100 mg kg-1), about 95% of the applied atrazine was degraded over the same period. Additionally, linear fitting of data indicated that the total enzymatic activity index (TEI) and bacterial α-diversity index were negatively correlated with atrazine applied concentration. The atrazine had a greater effect on bacterial beta diversity after 120 days, which differentiated species clusters treated with low and high atrazine concentrations. Soil bacterial community structure and function were affected by atrazine, especially at high atrazine concentrations (80 - 100 mg kg-1). Key microorganisms such as Sphingomonas and Nocardioides were identified as biomarkers for atrazine dissipation. Functional prediction indicated that most metabolic pathways might be involved in atrazine dissipation. Overall, the findings enhance our understanding of the factors driving atrazine degradation in black soil and supports the use of biomarkers as indicators of atrazine dissipation.

Magnetic biochar/quaternary phosphonium salt reduced antibiotic resistome and pathobiome on pakchoi leaves.

Antibiotic resistance genes (ARGs) and human pathogenic bacteria (HPB) in leafy vegetable is a matter of concern as they can be transferred from soil, atmosphere, and foliar sprays, and poses a potential risk to public health. While traditional disinfection technologies are effective in reducing the presence of ARGs and HPB in soil. A new technology, foliar spraying with magnetic biochar/quaternary ammonium salt (MBQ), was demonstrated and applied to the leaf surface. High-throughput quantitative PCR targeting 96 valid ARGs and 16 S rRNA sequencing were used to assess its efficacy in reducing ARGs and HPB. The results showed that spraying MBQ reduced 97.0 ± 0.81% of "high-risk ARGs", associated with seven classes of antibiotic resistance in pakchoi leaves within two weeks. Water washing could further reduce "high-risk ARGs" from pakchoi leaves by 19.8%- 24.6%. The relative abundance of HPB closely related to numerous ARGs was reduced by 15.2 ± 0.23% with MBQ application. Overall, this study identified the potential risk of ARGs from leafy vegetables and clarified the significant implications of MBQ application for human health as it offers a promising strategy for reducing ARGs and HPB in leafy vegetables.

Gut microbiota research nexus: One Health relationship between human, animal, and environmental resistomes.

The emergence and rapid spread of antimicrobial resistance is of global public health concern. The gut microbiota harboring diverse commensal and opportunistic bacteria that can acquire resistance via horizontal and vertical gene transfers is considered an important reservoir and sink of antibiotic resistance genes (ARGs). In this review, we describe the reservoirs of gut ARGs and their dynamics in both animals and humans, use the One Health perspective to track the transmission of ARG-containing bacteria between humans, animals, and the environment, and assess the impact of antimicrobial resistance on human health and socioeconomic development. The gut resistome can evolve in an environment subject to various selective pressures, including antibiotic administration and environmental and lifestyle factors (e.g., diet, age, gender, and living conditions), and interventions through probiotics. Strategies to reduce the abundance of clinically relevant antibiotic-resistant bacteria and their resistance determinants in various environmental niches are needed to ensure the mitigation of acquired antibiotic resistance. With the help of effective measures taken at the national, local, personal, and intestinal management, it will also result in preventing or minimizing the spread of infectious diseases. This review aims to improve our understanding of the correlations between intestinal microbiota and antimicrobial resistance and provide a basis for the development of management strategies to mitigate the antimicrobial resistance crisis.

Development and validation of an eDNA protocol for monitoring endemic Asian spiny frogs in the Himalayan region of Pakistan.

Wildlife monitoring programs are instrumental for the assessment of species, habitat status, and for the management of factors affecting them. This is particularly important for species found in freshwater ecosystems, such as amphibians, as they have higher estimated extinction rates than terrestrial species. We developed and validated two species-specific environmental DNA (eDNA) protocols and applied them in the field to detect the Hazara Torrent Frog (Allopaa hazarensis) and Murree Hills Frog (Nanorana vicina). Additionally, we compared eDNA surveys with visual encounter surveys and estimated site occupancy. eDNA surveys resulted in higher occurrence probabilities for both A. hazarensis and N. vicina than for visual encounter surveys. Detection probability using eDNA was greater for both species, particularly for A. hazarensis. The top-ranked detection model for visual encounter surveys included effects of both year and temperature on both species, and the top-ranked occupancy model included effects of elevation and year. The top-ranked detection model for eDNA data was the null model, and the top-ranked occupancy model included effects of elevation, year, and wetland type. To our knowledge, this is the first time an eDNA survey has been used to monitor amphibian species in the Himalayan region.

Bioaccumulation of Manure-borne antibiotic resistance genes in carrot and its exposure assessment.

The effect of manure application on the distribution and accumulation of antibiotic resistance genes (ARGs) in tissue of root vegetables remains unclear, which poses a bottleneck in assessing the health risks from root vegetables due to application of manure. Towards this goal, experiments were conducted in pots to investigate the distribution and bioaccumulation of ARGs in carrot tissues due to application of pig manure. The 144 ARGs targeting nine types of antibiotics were quantified by high throughput qPCR in the soil and plant samples. The rhizosphere was a hot spot for ARGs enrichment in the manured soil. The abundance, diversity, and bioaccumulation factors of ARGs in the phyllosphere were significantly higher than those of carrot root skin and tuber. Manure application increased bioaccumulation of 12 ARGs and 2 MGEs in carrot tuber with 124 the highest factor. The application of manure increased transfer of 10 ARGs and 3 MGEs from carrot skin to inner tuber by factors of 0.1-11.8. The average gene copy number of ARGs of per gram carrot root was about 4.8 × 104 and 1.1 × 106 in the control and the manured treatment, respectively. Children and adults may co-ingest 2.7 × 107 and 3.2 × 107 of ARGs copies/d from carrots grown with pig manure, using estimated human intake values. However, peeling may reduce the intake of ARGs by 28-91% and of MGEs by 46-59%. In conclusion, the application of pig manure increased the accumulation of ARGs in the skin of carrots, whereas peeling was an effective strategy to reduce the risk.

MicroRNA-based host response to toxicant exposure is influenced by the presence of gut microbial populations.

Segmented filamentous bacteria (SFB) and Bacteroides fragilis are known to interact with the host immune response through the aryl hydrocarbon receptor (Ahr). 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), an environmental toxicant and a high-affinity Ahr ligand has the potential to modify the effect of SFB and B. fragilis. MicroRNAs (miRNA) with their role in regulating gene expression post-transcriptionally, may potentially be used to observe such interactions between SFB, B. fragilis, and TCDD. However, little is known regarding the impact of gut microbial members on miRNA expression or its modulation in the presence of an environmental toxicant. This information is important in understanding toxicant-mediated dysbiosis in gut microbiome and the resulting human health impacts. In this study, C57BL/6 germ-free (GF) mice were colonized with SFB and B. fragilis and administered 30 µg/kg TCDD every 4 d for 28 d and miRNA were measured. Compared to GF mice, colonization with SFB resulted in an increase in up- and down-regulated Ileal miRNAs. TCDD treatment of this group decreased the number of upregulated miRNA and increased the number of down-regulated miRNAs. Association with SFB and B. fragilis together had a similar but less pronounced effect in response to TCDD treatment. TCDD treatment of GF mice had no miRNA expression response. Immune and inflammatory responses and T-cell differentiation were the key functions impacted by these miRNAs. Overall, these results reveal that the host response to toxicants may also depend on the presence of specific gut microbial populations.

Does anaerobic condition play a more positive role in dissipation of antibiotic resistance genes in soil?

The persistence of antibiotic resistance genes (ARGs) under the aerobic vs. anaerobic conditions is unknown, especially under different fertilization. Towards this goal, a microcosm experiment was carried out with chemical fertilized and manured soil under aerobic and anaerobic conditions. High throughput qPCR was used to analyze ARGs with 144 primer sets and sequencing for microorganisms. Completely different dynamics of ARGs were observed in soil under aerobic and anaerobic conditions, regardless of the fertilization type. ARGs had different half-lives, even though they confer resistance to the same type of antibiotics. Aminoglycoside, chloramphenicol, macrolide - lincosamide - streptogramin B (MLSB) and tetracycline resistance genes were significantly accumulated in the aerobic soils. Anaerobic soil possessed a higher harboring capacity for exogenous microorganisms and ARGs than aerobic soil. The interaction between ARGs and mobile genetic elements (MGEs) in manured soil under aerobic condition was more pronounced than the anaerobic condition. These findings unveil that anaerobic soil could play a more positive role in reducing potential risk of ARGs in the farmland environment.

Alterations in the Endophyte-Enriched Root-Associated Microbiome of Rice Receiving Growth-Promoting Treatments of Urea Fertilizer and Rhizobium Biofertilizer.

We examined the bacterial endophyte-enriched root-associated microbiome within rice (Oryza sativa) 55 days after growth in soil with and without urea fertilizer and/or biofertilization with a growth-promotive bacterial strain (Rhizobium leguminosarum bv. trifolii E11). After treatment to deplete rhizosphere/rhizoplane communities, washed roots were macerated and their endophyte-enriched communities were analyzed by 16S ribosomal DNA 454 amplicon pyrosequencing. This analysis clustered 99,990 valid sequence reads into 1105 operational taxonomic units (OTUs) with 97% sequence identity, 133 of which represented a consolidated core assemblage representing 12.04% of the fully detected OTU richness. Taxonomic affiliations indicated Proteobacteria as the most abundant phylum (especially α- and γ-Proteobacteria classes), followed by Firmicutes, Bacteroidetes, Verrucomicrobia, Actinobacteria, and several other phyla. Dominant genera included Rheinheimera, unclassified Rhodospirillaceae, Pseudomonas, Asticcacaulis, Sphingomonas, and Rhizobium. Several OTUs had close taxonomic affiliation to genera of diazotrophic rhizobacteria, including Rhizobium, unclassified Rhizobiales, Azospirillum, Azoarcus, unclassified Rhizobiaceae, Bradyrhizobium, Azonexus, Mesorhizobium, Devosia, Azovibrio, Azospira, Azomonas, and Azotobacter. The endophyte-enriched microbiome was restructured within roots receiving growth-promoting treatments. Compared to the untreated control, endophyte-enriched communities receiving urea and/or biofertilizer treatments were significantly reduced in OTU richness and relative read abundances. Several unique OTUs were enriched in each of the treatment communities. These alterations in structure of root-associated communities suggest dynamic interactions in the host plant microbiome, some of which may influence the well-documented positive synergistic impact of rhizobial biofertilizer inoculation plus low doses of urea-N fertilizer on growth promotion of rice, considered as one of the world's most important food crops.

Composting increased persistence of manure-borne antibiotic resistance genes in soils with different fertilization history.

Different long-term fertilization regimes may change indigenous microorganism diversity in the arable soil and thus might influence the persistence and transmission of manure-born antibiotic resistance genes (ARGs). Different manure origins and composting techniques might affect the fate of introduced ARGs in farmland. A four-month microcosm experiment was performed using two soils, which originated from the same field and applied with the same chemical fertilizer or swine manure for 26 years, to investigate the dynamics of ARGs in soil amended with manure or compost from the farm and an agro-technology company. High throughput qPCR and sequencing were applied to quantify ARGs using 144 primer sets and microorganism in soil. Fertilization history had little effect on dynamics of manure-borne ARGs in soil regardless of manure origin or composting. Very different half-lives of ARGs and mobile genetic elements from farm manure and commercial manure were observed in both soils. Composting decreased abundance of most ARGs in manure, but increased the persistence of manure-introduced ARGs in soil irrespective of fertilization history, especially for those from farm manure. These findings help understanding the fate of ARGs in manured soil and may inform techniques to mitigate ARGs transmission.

Direct or DNA Extraction-Free Amplification and Quantification of Foodborne Pathogens.

The use of direct nucleic acid amplification of pathogens from food matrices has the potential to reduce time to results over DNA extraction-based approaches as well as traditional culture-based approaches. Here we describe protocols for assay design and experiments for direct amplification of foodborne pathogens in food sample matrices using loop-mediated isothermal amplification (LAMP) and polymerase chain reaction (PCR). The examples provided include the detection Escherichia coli in milk samples and Salmonella in pork meat samples. This protocol includes relevant reagents and methods including obtaining target sequences, assay design, sample processing, and amplification. These methods, though used for specific example matrices, could be applied to many other foodborne pathogens and sample types.

Abundance of Chlorinated Solvent and 1,4-Dioxane Degrading Microorganisms at Five Chlorinated Solvent Contaminated Sites Determined via Shotgun Sequencing.

Shotgun sequencing was used for the quantification of taxonomic and functional biomarkers associated with chlorinated solvent bioremediation in 20 groundwater samples (five sites), following bioaugmentation with SDC-9. The analysis determined the abundance of (1) genera associated with chlorinated solvent degradation, (2) reductive dehalogenase (RDases) genes, (3) genes associated with 1,4-dioxane removal, (4) genes associated with aerobic chlorinated solvent degradation, and (5) D. mccartyi genes associated with hydrogen and corrinoid metabolism. The taxonomic analysis revealed numerous genera previously linked to chlorinated solvent degradation, including Dehalococcoides, Desulfitobacterium, and Dehalogenimonas. The functional gene analysis indicated vcrA and tceA from D. mccartyi were the RDases with the highest relative abundance. Reads aligning with both aerobic and anaerobic biomarkers were observed across all sites. Aerobic solvent degradation genes, etnC or etnE, were detected in at least one sample from each site, as were pmoA and mmoX. The most abundant 1,4-dioxane biomarker detected was Methylosinus trichosporium OB3b mmoX. Reads aligning to thmA or Pseudonocardia were not found. The work illustrates the importance of shotgun sequencing to provide a more complete picture of the functional abilities of microbial communities. The approach is advantageous over current methods because an unlimited number of functional genes can be quantified.

Long-Term Effect of Different Fertilization and Cropping Systems on the Soil Antibiotic Resistome.

Different fertilization and cropping systems may influence short- and long-term residues of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in soil. Soils from dryland (peanut) and paddy (rice) fields, which originated from the same nonagricultural land (forested), were treated with either chemical fertilizer, composted manure, or no fertilizer for 26 years before sampling, which occurred one year after the last applications. ARGs and MGEs were investigated using highly parallel qPCR and high-throughput sequencing. Six of the 11 antibiotics measured by LC-MS/MS were detected in the manure applied soil, but not in the nonmanured soils, indicating their source was from previous manure applications. Compared to the unfertilized control, manure application did not show a large accumulation of ARGs in either cropping system but there were some minor effects of soil management on indigenous ARGs. Paddy soil showed higher accumulation of these ARGs, which corresponded to higher microbial biomass than the dryland soil. Chemical fertilizer increased relative abundance of these ARGs in dryland soil but decreased their relative abundance in paddy soil. These results show how long-term common soil management practices affect the abundance and type of ARGs and MGEs in two very different soil environments, one aerobic and the other primarily anaerobic.

Antimicrobial Resistance in the Environment.

This review su mmarizes selected publications from 2017 highlighting the occurrence of antimicrobial resistance (AMR) genes in the environment with emphasis on the aquatic environment. The review also covers different treatment technologies being developed for AMR genes as an environmental contaminant. The progress made in the area of AMR gene databases and tools is also reviewed. Besides a brief introduction, the content is categorized into three main sections: i) Occurrence of AMR in the Environment, ii) Treatment technologies for AMR, and iii) AMR databases and tools.

Primer set 2.0 for highly parallel qPCR array targeting antibiotic resistance genes and mobile genetic elements.

The high-throughput antibiotic resistance gene (ARG) qPCR array, initially published in 2012, is increasingly used to quantify resistance and mobile determinants in environmental matrices. Continued utility of the array; however, necessitates improvements such as removing or redesigning questionable primer sets, updating targeted genes and coverage of available sequences. Towards this goal, a new primer design tool (EcoFunPrimer) was used to aid in identification of conserved regions of diverse genes. The total number of assays used for diverse genes was reduced from 91 old primer sets to 52 new primer sets, with only a 10% loss in sequence coverage. While the old and new array both contain 384 primer sets, a reduction in old primer sets permitted 147 additional ARGs and mobile genetic elements to be targeted. Results of validating the updated array with a mock community of strains resulted in over 98% of tested instances incurring true positive/negative calls. Common queries related to sensitivity, quantification and conventional data analysis (e.g. Ct cutoff value, and estimated genomic copies without standard curves) were also explored. A combined list of new and previously used primer sets is provided with a recommended set based on redesign of primer sets and results of validation.

MicroRNAs-Based Inter-Domain Communication between the Host and Members of the Gut Microbiome.

The gut microbiome is an important modulator of host gene expression, impacting important functions such as the innate immune response. Recent evidence suggests that the inter-domain communication between the gut microbiome and host may in part occur via microRNAs (small, non-coding RNA molecules) which are often differentially expressed in the presence of bacteria and can even be released and taken up by bacteria. The role of microRNAs in microbiome-host communication in intestinal diseases is not fully understood, particularly in diseases impacted by exposure to environmental toxicants. Here, we review the present knowledge in the areas of microbiome and microRNA expression-based communication, microbiome and intestinal disease relationships, and microRNA expression responses to intestinal diseases. We also examine potential links between host microRNA-microbiota communication and exposure to environmental toxicants by reviewing connections between (i) toxicants and microRNA expression, (ii) toxicants and gut diseases, and (iii) toxicants and the gut microbiome. Future multidisciplinary research in this area is needed to uncover these interactions with the potential to impact how gut-microbiome associated diseases [e.g., inflammatory bowel disease (IBD) and many others] are managed.

Isothermal amplification of environmental DNA (eDNA) for direct field-based monitoring and laboratory confirmation of Dreissena sp.

Loop-mediated isothermal amplification (LAMP) of aquatic invasive species environmental DNA (AIS eDNA) was used for rapid, sensitive, and specific detection of Dreissena sp. relevant to the Great Lakes (USA) basin. The method was validated for two uses including i) direct amplification of eDNA using a hand filtration system and ii) confirmation of the results after DNA extraction using a conventional thermal cycler run at isothermal temperatures. Direct amplification eliminated the need for DNA extraction and purification and allowed detection of target invasive species in grab or concentrated surface water samples, containing both free DNA as well as larger cells and particulates, such as veligers, eggs, or seeds. The direct amplification method validation was conducted using Dreissena polymorpha and Dreissena bugensis and uses up to 1 L grab water samples for high target abundance (e.g., greater than 10 veligers (larval mussels) per L for Dreissena sp.) or 20 L samples concentrated through 35 µm nylon screens for low target abundance, at less than 10 veligers per liter water. Surface water concentrate samples were collected over a period of three years, mostly from inland lakes in Michigan with the help of a network of volunteers. Field samples collected from 318 surface water locations included i) filtered concentrate for direct amplification validation and ii) 1 L grab water sample for eDNA extraction and confirmation. Though the extraction-based protocol was more sensitive (resulting in more positive detections than direct amplification), direct amplification could be used for rapid screening, allowing for quicker action times. For samples collected between May and August, results of eDNA direct amplification were consistent with known presence/absence of selected invasive species. A cross-platform smartphone application was also developed to disseminate the analyzed results to volunteers. Field tests of the direct amplification protocol using a portable device (Gene-Z) showed the method could be used in the field to obtain results within one hr (from sample to result). Overall, the direct amplification has the potential to simplify the eDNA-based monitoring of multiple aquatic invasive species. Additional studies are warranted to establish quantitative correlation between eDNA copy number, veliger, biomass or organismal abundance in the field.

Most probable number with visual based LAMP for the quantification of reductive dehalogenase genes in groundwater samples.

The remediation of chlorinated solvent contaminated sites frequently involves bioaugmentation with mixed cultures containing Dehalococcoides mccartyi. Their activity is then examined by quantifying reductive dehalogenase (RDase) genes. Recently, we described a rapid, low cost approach, based on loop mediated isothermal amplification (LAMP), which allowed for the visual detection of RDase genes from groundwater. In that study, samples were concentrated (without DNA extraction), incubated in a water bath (avoiding the use of a thermal cycler) and amplification was visualized by the addition of SYBR green (post incubation). Despite having a detection limit less than the threshold recommended for effective remediation, the application of the assay was limited because of the semi-quantitative nature of the data. Moreover, the assay was prone to false positives due to the aerosolization of amplicons. In this study, deoxyuridine triphosphate (dUTP) and uracil DNA glycosylase (UNG) were incorporated into the assay to reduce the probability of false positives. Optimization experiments revealed a UNG concentration of 0.2units per reaction was adequate for degrading trace levels of AUGC based contamination (~1.4×104 gene copies/reaction) without significant changes to the detection limit (~100 gene copies/reaction). Additionally, the optimized assay was used with the most probable number (MPN) method to quantify RDase genes (vcrA and tceA) in multiple groundwater samples from a chlorinated solvent contaminated site. Using this approach, gene concentrations were significantly correlated to concentrations obtained using traditional methods (qPCR and DNA templates). Although the assay underestimated RDase genes concentrations, a strong correlation (R2=0.78 and 0.94) was observed between the two data sets. The regression equations obtained will be valuable to determine gene copies in groundwater using the newly developed, low cost and time saving method.

Antimicrobial Resistance in the Environment.

This review summarizes selected publications of 2016 with emphasis on occurrence and treatment of antibiotic resistance genes and bacteria in the aquatic environment and wastewater and drinking water treatment plants. The review is conducted with emphasis on fate, modeling, risk assessment and data analysis methodologies for characterizing abundance. After providing a brief introduction, the review is divided into the following four sections: i) Occurrence of AMR in the Environment, ii) Treatment Technologies for AMR, iii) Modeling of Fate, Risk, and Environmental Impact of AMR, and iv) ARG Databases and Pipelines.

Modulatory Influence of Segmented Filamentous Bacteria on Transcriptomic Response of Gnotobiotic Mice Exposed to TCDD.

Environmental toxicants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), an aryl hydrocarbon receptor (AhR), are known to induce host toxicity and structural shifts in the gut microbiota. Key bacterial populations with similar or opposing functional responses to AhR ligand exposure may potentially help regulate expression of genes associated with immune dysfunction. To examine this question and the mechanisms for AhR ligand-induced bacterial shifts, C57BL/6 gnotobiotic mice were colonized with and without segmented filamentous bacteria (SFB) - an immune activator. Mice were also colonized with polysaccharide A producing Bacteroides fragilis - an immune suppressor to serve as a commensal background. Following colonization, mice were administered TCDD (30 µg/kg) every 4 days for 28 days by oral gavage. Quantified with the nCounter® mouse immunology panel, opposing responses in ileal gene expression (e.g., genes associated with T-cell differentiation via the class II major histocompatibility complex) as a result of TCDD dosing and SFB colonization were observed. Genes that responded to TCDD in the presence of SFB did not show a significant response in the absence of SFB, and vice versa. Regulatory T-cells examined in the mesenteric lymph-nodes, spleen, and blood were also less impacted by TCDD in mice colonized with SFB. TCDD-induced shifts in abundance of SFB and B. fragilis compared with previous studies in mice with a traditional gut microbiome. With regard to the mouse model colonized with individual populations, results indicate that TCDD-induced host response was significantly modulated by the presence of SFB in the gut microbiome, providing insight into therapeutic potential between AhR ligands and key commensals.

TCDD administered on activated carbon eliminates bioavailability and subsequent shifts to a key murine gut commensal.

Activated carbon (AC) is an increasingly attractive remediation alternative for the sequestration of dioxins at contaminated sites globally. However, the potential for AC to reduce the bioavailability of dioxins in mammals and the residing gut microbiota has received less attention. This question was partially answered in a recent study examining 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced hallmark toxic responses in mice administered with TCDD sequestered by AC or freely available in corn oil by oral gavage. Results from that study support the use of AC to significantly reduce the bioavailability of TCDD to the host. Herein, we examined the bioavailability of TCDD sequestered to AC on a key murine gut commensal and the influence of AC on the community structure of the gut microbiota. The analysis included qPCR to quantify the expression of segmented filamentous bacteria (SFB) in the mouse ileum, which has responded to TCDD-induced host toxicity in previous studies and community structure via sequencing the 16S ribosomal RNA (rRNA) gene. The expression of SFB 16S rRNA gene and functional genes significantly increased with TCDD administered with corn oil vehicle. Such a response was absent when TCDD was sequestered by AC. In addition, AC appeared to have a minimal influence on murine gut community structure and diversity, affecting only the relative abundance of Lactobacillaceae and two other groups. Results of this study further support the remedial use of AC for eliminating bioavailability of TCDD to host and subsequent influence on the gut microbiome.