Cellulose diacetate (CDA) is a biobased plastic that is used widely in consumer products. CDA is considered a promising alternative to conventional thermoplastics due to its susceptibility to biodegradation in a wide range of environmental compartments. Despite widespread evidence for the degradation of CDA, relatively little is known about the microbial communities that drive degradation, particularly in the ocean. Here, we studied the biodegradation of CDA-based materials (i.e., fabric, film, and foam) and positive and negative controls in a continuous-flow natural seawater mesocosm and investigated the responses of native microbial communities. Rapid degradation of CDA-based materials and positive controls occurred, with more than 65% of the initial mass degraded within three months. Microbial community analysis based on the 16S rRNA amplicon sequencing revealed that material type (i.e., CDA vs. controls), incubation time, material morphology (i.e., fabric vs. film), and plasticizer content controlled the structure of microbial communities. Bacterial taxa affiliated with the orders of Arenicellales, Cytophagales, Micavibrionales, Pseudomonadales, Rhizobiales, and Thermoanaerobaculales potentially initiated the degradation (i.e., deacetylation) of CDA film and fabric. These taxa were notably distinct from CDA-degrading microbes reported in other environmental compartments. Collectively, the findings lend further support for CDA as a promising next-generation, high-utility, and low-persistence plastic material. Future research should prioritize a more detailed understanding of the microbial species and enzymes that drive CDA degradation in marine environments, potentially leading to the design of CDA materials with even lower environmental persistence or novel biotechnologies for accelerated degradation of CDA waste in engineered systems.

Although studies exploring per- and polyfluoroalkyl substances (PFAS) biotransformation have been increasing in number, nearly all reported to-date have been limited to batch reactors. Thus, the potential effects of dynamic flow conditions on PFAS biotransformation and associated soil microbial community dynamics in water-saturated soil are unknown. In this study, PFAS biotransformation was investigated in one-dimensional columns packed with an aqueous film-forming foam (AFFF)-impacted soil. A common constituent in AFFFs, 6:2 fluorotelomer sulfonate (6:2 FTS) was selected for investigation. The 305-day column experiments demonstrated that 6:2 FTS biotransformation was rate-limited under tested flow conditions (i.e., pore-water velocity of 2.4-3.7 cm/day). Biotransformation increased 22-26% when hydraulic residence time increased from 4.1 to 6.3 days. Flow interruptions (2-7 days) were found to have a similar benefit that persisted over the 6-7 pore volumes following flow resumption. Additionally, under flowing conditions, less time was required for a similar extent of 6:2 FTS biotransformation compared to that measured in microcosm studies (e.g., 6.3 vs. 28-56 days). Throughout the experiments, distinctions between planktonic (PL) and porous media-attached (PMA) microbial community composition and dynamics were observed, which was attributed to oxygen availability, toxicity of 6:2 FTS and byproducts, and distinct microbial roles in transformation. Genus Pseudomonas dominated in PL microbial communities, however, in PMA microbial community, Rhodococcus decreased and Pelotomaculum increased along the flow path, suggesting their involvement in early- and late-stage 6:2 FTS biotransformation, respectively. Overall, these findings demonstrate that dynamic flow conditions can affect the rate and extent of PFAS biotransformation in water-saturated soil.

In this contribution, we present recent findings associating pharmaceutical biotransformations with putative microbial clades and enzymes responsible for curbing methane emissions and removing nitrate in shallow, open-water constructed wetlands. Using field-scale geochemical and metatranscriptomic profiles to inform a series of bench-scale inhibition microcosms, we arrived at two primary conclusions. First, aerobic methane-oxidizing activity stimulates the biotransformation of the antibiotic sulfamethoxazole. Second, nitrate-reducing activity putatively catalyzed by membrane-bound nitrate reductase enzymes regulates the biotransformation of the antiviral emtricitabine under anoxic conditions. Field-scale evidence for these associations includes in-situ microbial transcription of methane-oxidizing (pmoCAB) and nitrate-reducing (narGHI) genes in parallel with greenhouse gas fluxes, nitrate porewater profiles, and detection of parent and daughter biotransformation products. In-situ observations informed laboratory inhibition assays targeting methane monooxygenase (via acetylene and allylthiourea) and the membrane-bound nitrate reductase (via chlorate) which successfully suppressed aerobic methane oxidation and anoxic nitrate reduction in tandem with the transformations of sulfamethoxazole and emtricitabine, respectively. Although the molecular mechanism requires further validation, our integrated lines of evidence point toward particulate methane monooxygenase cometabolism as the likely pathway of sulfamethoxazole biotransformation. Given transformation product evidence for an oxidative pathway with emtricitabine, we hypothesize that enzymes or abiotic reactions associated with membrane-bound nitrate reductase activity may regulate biotransformation under anoxic conditions. Our findings have implications for the fate and transport of these and other trace organic contaminants, with possible opportunities to promote the synergistic attenuation of pharmaceuticals, methane, and nitrogen in nature-based and perhaps conventional wastewater treatment systems.

Widespread environmental contamination by heavy metals, perfluorinated compounds, and a host of other toxic organics—paired with the rapidly progressing climate crisis—necessitates sustainable soil and groundwater remediation schemes. The use of plants for phytoremediation is a carbon-negative, self-sustaining, and inexpensive approach to remove and transform nonpoint sources of environmental contamination. Despite these attractive features, phytoremediation is exceedingly time consuming due to slow kinetics or low levels of biomass production, limiting their practical application to low-value lands. Herein, we quantitatively evaluate the potential for nanotechnology to enable the next generation of phytoremediators by conferring non-native functions to plants via introduced nanomaterials. We first model contaminant accumulation in plants as fluidic resistors-in-series, comparing common, hypertolerant, and hyperaccumulating plants to elucidate the bottleneck for rapid sequestration. This approach for contaminant transport is then extended to nanoparticle (NP) uptake itself to parameterize the predicted outcome of using nanotechnologies to enhance the rate of contaminant uptake in plants. We apply a thermodynamic lipid-NP interaction model to quantify design parameters for increasing NP root-to-shoot translocation in plants. Our findings suggest an order-of-magnitude increase in contaminant uptake rate is possible with NP-mediated schemes. Plant nanobionics thus lends itself as an exciting technique to engineer high biomass, non-hyperaccumulating plants as fit-for-purpose, next-generation phytoremediators.

Nitrate-dependent iron oxidation (NDFO) is a novel mechanism for microbial bioremediation of metal and metalloid contaminants due to their propensity for sorption to iron minerals produced during NDFO, and, for some contaminants, the possibility of concurrent bioreduction. This is the first work to investigate NDFO for selenium removal. Typically, when both nitrate and selenium are present, nitrate is reduced first followed by bioreduction of selenate and selenite to elemental selenium. The iron (oxy)hydroxides produced by NDFO could aid selenium removal by sorbing selenite, and to a lesser extent selenate; coprecipitating with selenium; and catalyzing reduction of selenite to Se(0). This research characterized the effects of NDFO on selenium and nickel remediation in terms of contaminant removal rates, extents, and mechanisms. Sediment and influent water from a subsurface bioreactor treating mining wastewater were used to construct batch bioreactors, which were amended with either Fe(II) or methanol to test contaminant removal in NDFO vs. heterotrophic microbial communities. Both Fe(II) and methanol reactors removed total selenium to below the quantification limit, but Fe(II) reactors removed it more rapidly, likely due to sorption of selenite. For nickel, removal to below the detection limit was achieved with methanol amendment, while Fe(II) amendment resulted in 42-95% removal. This was likely due to precipitation of nickel sulfide during sulfate reduction in methanol-amended reactors. NDFO could improve selenium bioremediation efficiency, but its interactions with other contaminants must also be considered. Better understanding of the biogeochemical conditions that stimulate NDFO is also needed for practical application.