The cultivation and consumption of transgenic crops continues to be a widely debated topic, as the potential ecological impacts are not fully understood. In particular, because antibiotic resistance genes (ARGs) have historically been used as selectable markers in the genetic engineering of transgenic crops, it is important to determine if the genetic constructs found in decomposing transgenic crops persist long enough in the environment and if they can be transferred horizontally to indigenous microorganisms. In the present study, we address the question of persistence. Others have also estimated the DNA adsorption capacity of various clays, but have done so by manipulating the surface charge and size of particles tested which may overestimate sorption and underestimate the DNA available for horizontal transfer. In the present study, isotherms were generated using model Calf Thymus DNA and transgenic maize DNA without surface modification. Montmorillonite, kaolinite, and 3 soil mixtures with varying clay content were used in this study. The adsorption capacity of pure montmorillonite and kaolinite minerals was found to be one to two orders of magnitude less than previously estimated likely due to the distribution of clay particle sizes and heteroionic particle surface charge. However, it appears that a substantial amount of DNA is still able to adsorb onto these matrices (up to 200 mg DNA per gram of clay) suggesting the potential availability of free transgenic DNA in the environment may still be significant. Future studies should be conducted to determine the fate of these genes in agricultural soils.

The increasing occurrence of tetrabromobisphenol A (TBBPA) in the environment is raising questions about its potential environmental health impacts as it has been shown to cause various deleterious effects in humans. The fact that the highest concentrations of TBBPA have been reported in wastewater sludge is concerning as effluent discharge and biosolids land application are likely a route by which TBBPA can be further disbursed to the environment. Our objectives in this study were to evaluate the effect of biochar (BC) and activated carbon (AC) in promoting the biodegradation of TBBPA, and characterize the response of anaerobic sludge microbial communities following amendments. Both carbonaceous amendments were found to promote the reductive debromination of TBBPA. Nearly complete transformation of TBBPA to BPA was observed in the amended reactors ~20 days earlier than in the control reactors. In particular, the transformation of diBBPA to monoBBPA, which appears to be the rate-limiting step, was accelerated in the presence of either amendment. Overall, microbial taxa responding to the amendments, i.e., ‘sensitive responders’, represented a small proportion of the community (i.e., 7.2%), and responded positively. However, although both amendments had a similar effect on TBBPA degradation, the taxonomic profile of the sensitive responders differed greatly from one amendment to the other. BC had a taxonomically broader and slightly more pronounced effect than AC. This work suggests that BC and AC show great potential to promote the biodegradation of TBBPA in anaerobic sludge, and their integration into wastewater treatment processes may be helpful for removing TBBPA and possibly other emerging hydrophobic contaminants.

Due to the sequence homology between the bacterial 16S rRNA gene and plant chloroplast and mitochondrial DNA, the taxonomic characterization of plant microbiome using amplicon-based high throughput sequencing often results in the overwhelming presence of plant-affiliated reads, preventing the thorough description of plant-associated microbial communities. In this work we developed a PCR blocking primer assay targeting the taxonomically informative V5-V6 region of the 16S rRNA gene in order to reduce plant DNA co-amplification, and increase diversity coverage of associated prokaryotic communities. Evaluation of our assay on the characterization of the prokaryotic endophytic communities of Zea mays, Pinus taeda and Spartina alternifora leaves led to significantly reducing the proportion of plant reads, yielded 20 times more prokaryotic reads and tripled the number of detected OTUs compared to a commonly used V5-V6 PCR protocol. To expand the application of our PCR-clamping assay across a wider taxonomic spectrum of plant hosts, we additionally provide an alignment of chloroplast and mitochondrial DNA sequences encompassing more than 200 terrestrial plant families as a supporting tool for customizing our blocking primers.

High concentrations of pesticides enter surface waters following agricultural application, raising environmental and human health concerns. The use of photoreactive nanoparticles has shown promise for contaminant degradation and surface water remediation. However, it remains uncertain how the complexity of natural waters will impact the photodegradation process. Here, we investigate the photoreactivity of titanium dioxide nanoparticles, the capability to degrade the pesticide chlorpyrifos, and the effect of and impact on bacteria during the photodegradation process. Loss of chlorpyrifos in solution resulted solely from photocatalytic oxidation, with 80% degradation observed after 24 h in our reactor, either in the presence or absence of bacteria. Degradation of chlorpyrifos to chlorpyrifos oxon and 3,5,6-trichloro-2-pyridinol was observed via LC/MS-MS and effectively modeled for the given reactor conditions. Bacterial inactivation occurred over 60 min and was not impacted by the presence of chlorpyrifos. The relative affinity of bacteria and chlorpyrifos for the nanoparticle surface decreased the amount of Reactive Oxygen Species (ROS) detected in the bulk by up to 94%, suggesting that ROS measurements in simplified systems may overestimate the reactivity of photoreactive nanoparticles in complex environments.

Semivolatile organic compounds (SVOCs) are widely detected in many indoor environments due to their frequent use in building materials, textiles, furniture, electronics, and other consumer products. Biomarkers of SVOC exposures have been consistently measured in biological samples across the globe, presenting uncertainty about their potential impacts on sensitive populations. To begin unravelling the dynamics between gut microbiome maturation and chronic exposure to complex chemical mixtures, this study characterized the prokaryotic and fungal gut microbiomes of children (ages 3− 6) in a North Carolina cohort and examined their relationships with SVOC exposures. SVOC biomarkers were detected ubiquitously in pooled urine samples, with 29 compounds detected in >95% of samples. In total, 61 bacterial taxon−biomarker and 24 fungal taxon−biomarker pairs displayed statistically significant relationships (i.e., minimum positive r s ≥ 0.2 or minimum negative r s ≤ −0.2; p < 0.05), with disparate trends noted for bacteria and fungi. Sm-PFOS was associated with declines in several bacterial taxa (r s ≤ −0.21; p ≤ 0.05), while phthalate metabolites like MHiBP were negatively associated with fungi (r s ≤ −0.45). Finally, 10 genera historically capable of reductive dehalogenation displayed significant positive associations with halogenated SVOCs (e.g., biomarkes of chlorobenzenes such as 2,4-DCP), suggesting these compounds may act as a selective pressure within developing gut microbiomes.