Microplastics (MPs) have been widely detected in the soil environment. The Weishan Irrigation District is the largest irrigation area in the lower reaches of the Yellow River. However, little is known about MP pollution levels in the soils of this area. Forty-two soil samples, two water samples, and two organic fertilizer samples were collected to study the occurrence and sources of MP in the soils of four land use types. Different characteristics of MP were integrated to trace the sources of MP in soils and ecological risks associated with specific MP characteristics were evaluated. The average abundances of MPs in the soils of vegetable fields, crop fields, orchard fields, and woodlands were 900, 512, 615, and 633 items/kg, respectively. MPs were predominantly 0.2-1 mm in size (> 78 %), primarily blue/purple and transparent in color (> 60 %), mainly film, fiber, and fragment in shape (> 78 %), and mostly polyethylene in polymer type (> 36 %). Irrigation water, organic fertilizers, and plastic inputs are the major sources. Ecological risks based on MPs with specific characteristics were higher than those based on total MP. The source-based strategies developed are helpful to the prevention and control of MP pollution in irrigation districts.

Chemical modification can greatly improve the adsorption performance of materials. In this study, pristine pine bark (PB) was modified by phosphoric acid (PA-PB), dodecyl trimethylammonium bromide (DTAB-PB) and cetyl trimethylammonium bromide (CTAB-PB) to test their influence on remediating hexavalent chromium [Cr(IV)] contamination in water and soil systems. Under the optimal experimental conditions in solution, the reduction/adsorption capacities and removal rates of Cr(IV) follow the order of CTAB-PB > PA-PB > DTAB-PB > PB, with CTAB-PB showing the highest capacity of 88.1 mg g(-1). Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) indicated that adsorption coupled with reduction were the responsible mechanisms for Cr(IV) removal by pristine and modified PB, and modification with CTAB greatly improved Cr(IV) removal, especially the reduction of Cr(IV). When CTAB-PB and PB were applied in soil for a 30-day microcosm experiment, more than 93 % of Cr(IV) was converted into Cr(III) at four different addition levels (2, 5, 10, and 15 wt%) with CTAB-PB exhibiting a faster immobilization rate than PB. In conclusion, CTAB-PB showed better performance than PB and is a promising material for the remediation of Cr(IV) contamination in water and soil.

Many deep soil environments are anoxic due to the scarcity of O2, wherein NO3-, SO42-, Fe3+, Mn4+, and HCO3- (CO2) can function as terminal electron acceptors (TEAs). Anoxic biodegradation of PAHs using NO3- and SO42- as TEAs has been the subject of extensive research. However, information related to the degradation of PAHs under methanogenic conditions using CO2 as TEA is poorly understood, although it is a critical pathway in elimination of PAHs from anoxic soils. However, the low degradation rate of PAHs under anoxic conditions is the primary bottleneck restricting the promotion and application of this technology. Therefore, in this study, a low -temperature (< 50 degrees C) thermal enhanced biodegradation microcosm experiment was conducted using three temperatures (15 degrees C, 30 degrees C, and 45 degrees C) under methanogenic conditions. The results revealed that the limited PAH removal was somewhat compensated for by elevated temperature (e.g., 45 degrees C) compared to lower temperature (e.g., 15 degrees C or 30 degrees C), and removal efficiency of 2-, 3-and 4-ring PAHs (except for benz(a)anthracene (BaA)) obeyed the order of 45 degrees C > 30 degrees C > 15 degrees C. Kinetic analysis and t-test confirmed this and indicated that the promotion of PAH removal is more significant when temperature is raised from 30 degrees C to 45 degrees C than from 15 degrees C to 30 degrees C. Soil microbial communities were significantly affected by both the incubation time and temperature, and the changes in bacterial and archaeal communities were enhanced with increasing temperature. Network analysis demonstrated that soil microbes tended to cooccur rather than coexclude. The bacterial and archaeal cooccurrence network became less complex after incubation. The numbers of nodes, edges, and modules declined after 250 days of incubation, indicating that microbial function tends to be simple with prolonged incubation time. These results provide new insights and a scientific basis for the bioremediation of PAH-contaminated sites.

Phenanthrene (PHE) is widely distributed, and it can cause genotoxicity in humans by interacting with enzymes in the body. A current challenge for PHE bioremediation is the inhibitory effect of biotoxic intermediates on bacterial growth. Notably, the aerobic biotransformation processes for PHE in the presence of sophorolipids have been poorly studied. Here, a PHE-degrading strain was isolated from sediments and identified as Pseudomonas stutzeri and named LSH-PAH1. It was observed that 1-naphthol (a biotoxic substance that can inhibit strain growth) was produced during the PHE metabolism process of LSH-PAH1. The biodegradation ratio increased from 21.4% to 91.7% within 48 h after the addition of sophorolipids. Unexpectedly, this addition accelerated the metabolic process for 1-naphthol rather than causing its accumulation. The cometabolism of 1-naphthol and sophorolipids alleviated the biotoxic effects for the strain, which was verified by gene expression analysis. We identified a new PHE-degrading strain and provided a mechanism for PHE biodegradation using LSH-PAH1 with the addition of sophorolipids, which provides a reference for practical applications of the bioremediation of PHE and study of the cometabolism of biotoxic intermediates.

Mycobacterium sp. 16 F can degrade 94% of pyrene (20 ppm) in 4 days. To investigate its pyrene degradation mechanism, proteomic changes were analyzed using two-dimensional differential gel electrophoresis (2DE-DIGE). Comparative analysis of differential proteins revealed 91 differentially expressed protein spots after pyrene exposure. Among these, 65 spots were identified as 57 proteins. Further analysis revealed that 13 spots were involved in the pyrene degradation pathway, and most of these were dioxygenases and dehydrogenases. Further, 16 up-regulated expression protein spots were associated with four pathways that may be related to pyrene degradation. Bioinformatics analysis further revealed that the pentose phosphate and glycolytic pathways led to the production of amino acids and nucleotide precursors in pyrene-induced cells. The metabolites from these processes then entered the shikimate pathway via the beta-ketoadipate pathway in conjunction with the pyrene degradation pathway. This study provides a new model for the pyrene degradation pathway in Mycobacteria.

In situ anoxic bioremediation is an easy-to-use technology to remediate polycyclic aromatic hydrocarbon (PAH)-contaminated soil. Degradation of PAHs mediated by soil bacteria and archaea using CO2 as the electron acceptor is an important process for eliminating PAHs under methanogenic conditions; however, knowledge of the per-formance and mechanisms involved is poorly unveiled. In this study, the effectiveness and efficiency of NaHCO3 (CO2) as an electron acceptor to stimulate the degradation of PAHs by bacteria and archaea in highly contam-inated soil were investigated. The results showed that CO2 addition (EC2000) promoted PAH degradation compared to soil without added CO2 (EC0), with 4.18%, 9.01%-8.05%, and 6.19%-12.45% increases for 2-, 3 -and 4-ring PAHs after 250 days of incubation, respectively. Soil bacterial abundances increased with increasing incubation time, especially for EC2000 (2.90 x 108 g(-1) soil higher than EC0, p < 0.05). Different succession patterns of the soil bacterial and archaeal communities during PAH degradation were observed. According to the PCoA and ANOSIM results, the soil bacterial communities were greatly (ANOSIM: R = 0.7232, P = 0.001) impacted by electron acceptors, whereas significant differences in the archaeal communities were not observed (ANOSIM: R = 0.553, P = 0.001). Soil bacterial and archaeal co-occurrence network analyses showed that positive correlations outnumbered the negative correlations throughout the incubation period for both treat-ments (e.g., EC0 and EC2000), suggesting the prevalence of coexistence/cooperation within and between these two domains rather than competition. The higher complexity, connectance, edge, and node numbers in EC2000 revealed stronger linkage and a more stable co-occurrence network compared to EC0. The results of this study could improve the knowledge on the removal of PAHs and the responses of soil bacteria and archaea to CO2 application, as well as a scientific basis for the in situ anoxic bioremediation of PAH-contaminated industrial sites.

In order to explore the microbial communities and functions of activated sludge in an Anaerobic-anoxic-oxic (A²/O) process under the start-up of Actinic reaction enzyme system (ARES) system and to understand the impact of the ARES system in domestic sewage treatment process, the activated sludge microbial community structure in the A²/O process system before and after ARES system start-up was analyzed by Illumina-HiSeq 2000 high-throughput sequencing platform. By combining with the main parameters related to the effect of sewage treatment, we analyzed the environmental functions of the microbial communities. The microbial community structure of activated sludge was significantly different before and after the ARES system start-up. There were 9 main bacterial phyla in the system (average relative abundance ≥1%), accounting for 96%-98% of the total bacteria sequenced. After the ARES system was started, the relative abundance of Betaproteobacteria and Chlorobi increased by 3.45%-3.85% and 0.45%-2.61%, respectively. In the anaerobic unit, the relative abundance of Bacteroidetes increased by 12.97%, while the Actinobacteria and Firmicutes decreased by 9.60% and 1.45%, respectively. At the genus level of bacteria, the relative abundance of Denitratisoma increased by 0.80%-3.27%, while the Haliangium and Arcobacter decreased by 3.36%-4.52% and 1.48%-3.45%, respectively. The relative abundance of bacteria was significantly different before and after the ARES system start-up. There were 7 abundant fungi phyla (average relative abundance ≥1%) in the system. After the ARES system was started, the relative abundance of Rozellomycota decreased by 42.71%-46.77%. In the anaerobic unit, the relative abundance of Ascomycota decreased by 13.39%, while the relative abundance of Glomeromycota increased by 13.86%. At the genus level of fungi. The relative abundance of Entomophthoraceae sp. and Glomcromycota sp. increased by 31.35%-36.50% and 6.27%-13.84%, respectively, while the Rozellomycota sp. and Xylochrysis lucida decreased by 42.71%-46.77% and 3.67%-5.54%, respectively. Our results showed that the application of ARES system caused the response of the microbial community to environmental changes, especially for the fungi communities, in the meanwhile, improved the effluent quality, especially the removal rate of total nitrogen.

To reveal the molecular mechanism at the level of regulation of proteins in Rhodococcus sp. BAP-1 induced by fluoranthene comparative proteomic analysis was performed on proteins extracted from fluoranthene-exposed cells on 1 d, 3 d, 6 d and 8 d compared with control cells using isobaric tags for relative and absolute quantization (iTRAQ) labeling and LC-MS/MS analysis to access differentially expressed proteins. As a result, we detected a total of 897 significantly differentially expressed proteins, including 30 shared proteins in four comparison clusters. We were able to short-list 190, 329, 101 and 90 proteins that were over-represented, and 394, 234, 65 and 49 under-represented proteins, in 1d/control, 3d/control, 6d/control and 8d/control comparisons, respectively. Functional analysis relied on Clusters of Orthologous Groups (COG), gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed that fluoranthene significantly altered the expression of proteins involved in metabolic and biosynthesis processes. Furthermore, BAP-1 up-regulates aldehyde dehydrogenase, cytochrome c oxidase, and oligopeptide transport ATP-binding protein, while down-regulates several other proteins in order to adapt to fluoranthene exposure. These findings provide important clues to reveal fluoranthene degradation mechanism in BAP-1 and promote its bioremediation applications.

The pseudosolubilized medium-chain-length n-alkanes during biodegradation process, and optimization of medium composition and culture conditions for rhamnolipid production by Pseudomonas sp. DG17 using Plackett–Burman design and Box–Behnken design, were examined in this study. The results showed that pseudosolubilized concentration of C14 to C20 n-alkanes was higher than that of C24 to C26. After incubation for 120 h, pseudosolubilized C16H34 increased to 2.63 ± 0.21 mg. Meanwhile, biodegradation rates of n-alkanes decreased along with the increase of carbon chain length. Carbon-14 assay suggested that nonlabeled C14H30, C16H34, and C20H42 inhibited the biodegradation of 14C n-octadecane, and Pseudomonas sp. DG17 utilized different alkanes simultaneously. Three significant variables (substrate concentration, salinity, and C/N) that could influence rhamnolipid production were screened by Plackett–Burman design. Results of Box–Behnken design suggested that rhamnolipid concentration could be achieved at 91.24 mg L−1 (observed value) or 87.92 mg L−1 (predicted value) with the optimal levels of concentration, salinity, and C/N of 400 mg L−1, 1.5 %, and 45, respectively.