Surface modification significantly changed the effects of nano-polystyrene on sediment microbial communities and nitrogen metabolism

Nanoplastics pre-exposure to microbial consortium influencing their ability to degrade pollutants: "Stagnation effect" and "Self-recovery"

Nanoplastics (NPs) coexist with microorganisms in global water environmental systems, showing spatial-temporal differentiation. Therefore, studying the behavior of microorganisms previously exposed to NPs is particularly important. With 2,4-dichlorophenol (DCP)-degrading microflora as model microorganisms, this study found that higher dose (10, 100 mg/L) of polystyrene NPs pre-exposure inhibited bacterial DCP degradation prolonging the stagnation period, while lower dose (1 mg/L) of NPs on the contrary stimulated their degradation ability. The degradation delay coefficients (μ) showed a significant positive correlation with the duration of pre-exposure. Specifically, the μ values observed after 1 day, 3 days, and 9 days of pre-exposure to 10 mg/L NPs were 2.5, 2.9, and 3.8, respectively, while those for 100 mg/L NPs were 3.2, 4.0, and 5.1. In contrast, the control group without NPs exhibited a μ value of only 1.9. Pre-exposure caused NPs to enter bacterial cells, leading to oxidative damage, membrane impairment, and potential DNA damage. This carry-over toxicity suppressed the consortium's degradation efficiency of DCP. During the stagnation period, microorganisms were striving to redeem themselves, recovering their abilities of biofilm formation, chemotaxis and motility by upregulating the expression of wspA, mcp, and pilJ gene families, thus reinforcing inter-population regulatory cooperation, thereby restarting the DCP degradation. With the duration of pre-exposure to PS NPs increased, the recovery time required for bacterial communities also lengthened. It is crucial to pay attention to the biological responses to subsequent pollutants triggered by pre-exposure.

Bacillus subtilis, a promising bacterial candidate for trapping nanoplastics during water treatment

As a probiotic, Bacillus subtilis (B. subtilis) has a wide range of application values. In this study, the trap by B. subtilis and the effect of NPs on its growth physiology were studied. Confocal laser scanning microscopy (LCSM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed that PS-NPs were trapped by B. subtilis when they were exposed to PS-NPs. At this point, most of the PS-NPs are clustered around B. subtilis. Flow cytometry showed that at 10 mg/L, 73.7 % of PS-NPs' environmental state changed. The complexity of 9.73 %, 23.77 %, 43.27 %, and 65.13 % of B. subtilis increased at PS-NP concentrations of 10, 20, 50, and 200 mg/L, respectively. The increase in overall EPS secretion ranged from 0.51 ∼ 7.13 μg/mL after adding different concentrations of PS-NPs. The effect of different concentrations of PS-NPs on NAR activity ranged from -11.38 ∼ 16.2 %, on NIR activity from -17.90 ∼ 7.22 %, on NOR activity from -15.10 ∼ 7.69 % and on NO2R activity from -14.01 ∼ 17.03 %. These results indicated that B. subtilis can process nitrogen compounds in water while capturing NPs in the environment. They have the potential to be candidate bacteria in the water treatment process, and specific applications are needed to research further.

Responses of SNEDPR-AGS system under long-term exposure of polyethylene terephthalate microplastics for treating low C/N wastewater: Granular effect and microbial structure

The removal of nutrients in sewage treatment plants can be significantly impacted by carbon limitations, especially for treating low carbon to nitrogen ratio (C/N) wastewater, which can markedly increase operational costs. Simultaneous nitrification, endogenous denitrification, and phosphorus removal combined with aerobic granular sludge (SNEDPR-AGS) has emerged as one of the optimal processes for treating low C/N wastewater owing to its high carbon utilization efficiency; however, the long-term effect of microplastics (MPs) on this system remains unclear. This study investigated the granular effect and microbial response of an SNEDPR-AGS system for treating low C/N wastewater under long-term exposure (180 d) to polyethylene terephthalate microplastics (PET-MPs). The results showed that the integrity of the AGS structure was disrupted significantly as the PET-MP concentration increased, with clear AGS cracks appearing on days 180, 124, and 74 after exposure to 1, 10, and 100 mg/L of PET-MPs, respectively. Additionally, the addition of PET-MPs also inhibited denitrification and phosphorus removal due to a decrease in the relative abundance of functional genes (napAB, nirK/nirS, ppk1, ppk2, and ppx). Notably, both chemometric and high-throughput sequencing results indicated that the metabolic form of the system would shift from a polyphosphate-accumulating metabolism to a glycogen-accumulating metabolism. The reason may be that PET-MP stress inhibited the relative abundance of functional genes related to carbon, glycogen, phosphorus, and energy metabolism pathways in Candidatus Accumulibacter and Dechloromonas, but promoted their relative abundance of Candidatus Competibacter. Flow cytometry and molecular docking simulations have also demonstrated the direct toxic effects of PET-MPs on the SNEDPR-AGS system. The biological enhancement and functional recovery of damaged SNEDPR-AGS systems must be further investigated in future studies.

Pseudomonas Stutzeri may alter the environmental fate of polystyrene nanoplastics by trapping them with increasing extracellular polymers

Pseudomonas Stutzeri (P. stutzeri) is a denitrifying bacterium that is essential in biological nitrogen removal. To study the interaction between P. stutzeri and polystyrene nanoplastics (PS-NPs), the effects of PS-NPs posed on P. stutzeri were evaluated in terms of bacterial growth, physiology, denitrification function and extracellular polymers (EPS) secretion. Results of confocal laser scanning microscopy (LCSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and flow cytometry confirmed that PS-NPs were trapped by P. stutzeri. Exposure to PS-NPs inhibited bacterial growth and expression of denitrification-related genes, but unaffected the denitrifying enzyme activities. The enhanced secretion of EPS caused PS-NPs and bacterial aggregation. And the enzyme activity of SOD in P. stutzeri was increased while that of CAT was decreased. The results of flow cytometry showed that high concentrations of PS-NPs increased the complexity of P. stutzeri cells. These results reveal that P. stutzeri may be affected after trapping PS-NPs and alter their environmental fate as well. SYNOPSIS: This study contributes to the understanding of the possible effect of P. stutzeri on the distribution of PS-NPs and illustrates the potential impact of PS-NPs on P. stutzeri.

Nanoplastics enhance the denitrification process and microbial interaction network in wetland soils

With the widespread presence of plastic waste in ecosystems, it is imperative to understand the response of natural processes to micro- and nanoplastic pollution pressures. However, the effects of nanoplastics on biogeochemical cycles are still overlooked and controversial. This study investigated the effects of three particle sizes (100 μm, 7 μm, and 80 nm) of polystyrene (PS) micro/nanoplastics (0.08 % of mass concentration) on denitrification processes and nirS/nirK denitrifying bacterial communities in wetland soils. The results indicated that PS nanoplastics were found to significantly enhance denitrification rates from 21.30 to 54.73 μmol N2·h-1·kg-1, increasing by 1.57 times compared to the control. Exposure to nanoplastics caused shifts in the composition and structure of the nirS-type denitrifier community. LEfSe analysis, random forest, and Mantel tests revealed that nirS denitrifying bacteria, especially Sideroxydans, played a pivotal role in driving denitrification rates (Mantel's R = 0.24, p = 0.002), likely due to the faster release of organic substrates from nanoplastics. Microbial co-occurrence networks demonstrated that nanoplastic amendments fostered a denser denitrifier network and led to shifts in keystone species. Sideroxydans appeared more likely to cooperate with other bacteria, such as Burkholderiales, to complete denitrification processes. This study suggests that nanoplastics are a potentially stronger driver of denitrification than microplastics, providing insight into the impact of plastic pollutants on biogeochemical cycling in natural wetland ecosystems. Given the widespread distribution of wetlands, the potential increase in gaseous nitrogen emissions due to nanoplastics pollution warrants attention.

Comparison of Transgenerational Neurotoxicity between Pristine and Amino-Modified Nanoplastics in C. elegans

Increasing evidence has suggested that nanoplastic pollution has become a global concern. More importantly, transgenerational toxicity can be induced by nanoplastics at predicted environmentally relevant doses (ERDs). Considering that amino modification could increase nanoplastic toxicity, we compared transgenerational neurotoxicity between pristine polystyrene nanoparticle (PS-NP) and amino-modified PS-NP (NH2-PS-NP) in Caenorhabditis elegans. At 0.1-10 μg/L, NH2-PS-NP caused more severe transgenerational toxicity on locomotion and neuronal development. Accompanied with a difference in transgenerational neuronal damage, compared to PS-NP (10 μg/L), NH2-PS-NP (10 μg/L) induced more severe transgenerational activation of mec-4, crt-1, itr-1, and tra-3, which are required for the induction of neurodegeneration. Moreover, NH2-PS-NP (10 μg/L) caused more severe transgenerational inhibition in expressions of mpk-1, jnk-1, dbl-1, and daf-7 than PS-NP (10 μg/L), and RNA interference (RNAi) of these genes conferred susceptibility to the toxicity of PS-NP and NH2-PS-NP on locomotion and neuronal development. NH2-PS-NP (10 μg/L) further caused more severe transgenerational activation of germline ligand genes (ins-3, ins-39, daf-28, lin-44, egl-17, efn-3, and lag-2) than PS-NP (10 μg/L), and RNAi of these ligand genes caused resistance to the toxicity of PS-NP and NH2-PS-NP on locomotion and neuronal development. Our results highlighted more severe exposure risk of amino-modified nanoplastics at ERDs in causing transgenerational neurotoxicity in organisms.

Exposure to polystyrene nanoplastics induces abnormal activation of innate immunity via the cGAS-STING pathway

Endogenous immune defenses provide an intrinsic barrier against external entity invasion. Microplastics in the environment, especially those at the nanoscale (nanoplastics or NPs), may pose latent health risks through direct exposure. While links between nanoplastics and inflammatory processes have been established, detailed insights into how they may perturb the innate immune mechanisms remain uncharted. Employing murine and macrophage (RAW264.7) cellular models subjected to polystyrene nanoplastics (PS-NPs), our investigative approach encompassed an array of techniques: Cell Counting Kit-8 assays, flow cytometric analysis, acridine orange/ethidium bromide (AO/EB) fluorescence staining, cell transfection, cell cycle scrutiny, genetic manipulation, messenger RNA expression profiling via quantitative real-time PCR, and protein expression evaluation through western blotting. The results showed that PS-NPs caused RAW264.7 cell apoptosis, leading to cell cycle arrest, and activated the cGAS-STING pathway. This resulted in NF-κB signaling activation and increased pro-inflammatory mediator expression. Importantly, PS-NPs-induced activation of NF-κB and its downstream inflammatory cascade were markedly diminished after the silencing of the STING gene. Our findings highlight the critical role of the cGAS-STING pathway in the immunotoxic effects induced by PS-NPs. We outline a new mechanism whereby nanoplastics may trigger dysregulated innate immune and inflammatory responses via the cGAS/STING pathway.