Metabolic biotransformation of copper-benzo[a]pyrene combined pollutant on the cellular interface of Stenotrophomonas maltophilia

Effects of arsenic and trace metals on bacterial denitrification process from estuarine sediments and associated nitrous oxide emission

Coastal ecosystems currently face significant challenges due to nutrient enrichment and trace metal contamination. However, the effects of arsenic (As) and other trace metals (copper, lead, zinc, cadmium, mercury) on denitrification processes and nitrous oxide (N2O) emissions in estuarine sediments remain poorly understood. Here, we examined the influence of As and other trace metals on denitrification and N2O emissions in a single denitrifying strain, Marinobacter sp. MSD-1, isolated from metal-contaminated estuarine sediments based on its As(III)-oxidizing and denitrifying abilities and functional microbial composition. The results showed that As did not significantly affect the denitrification or N2O emission of MSD-1. However, Cd(II) at concentrations of 5-10 mg/L significantly induced the accumulation of N2O, while not significantly affecting the reduction of nitrate (NO3-) and nitrite (NO2-). The presence of As(III) further inhibited the N2O reduction under Cd exposure, but it had no significant effect on the N2O reduction after exposure to other trace metals. A negative correlation was observed between N2O reductase (NO2R) activity and N2O emissions, indicating that Cd(II) inhibits the reduction process of N2O mainly by suppressing the activity of NO2R. This study highlights the detrimental effects of cadmium on microbial denitrification and subsequent emissions of the greenhouse gas N2O, thereby improving our understanding of how estuarine and coastal ecosystems respond and adapt to trace metal pollution.

Biomolecular insights into the inhibition of heavy metals on reductive dechlorination of 2,4,6-trichlorophenol in Pseudomonas sp. CP-1

Influences of heavy metal exposure to the organohalide respiration process and the related molecular mechanism remain poorly understood. In this study, a non-obligate organohalide respiring bacterium, Pseudomonas sp. strain CP-1, was isolated and its molecular response to the five types of commonly existed heavy metal ions were thoroughly investigated. All types of heavy metal ions posed inhibitory effects on 2,4,6-trichlorophenol dechlorination activity and cell growth with the varied degree. Exposure to Cu (II) showed the most serious inhibitive effects on dechlorination even at the lowest concentration of 0.05 mg/L, while the inhibition by As (V) was the least with the removal kinetic constant k decreased to 0.05 under 50 mg/L. Further, multi-omics analysis found compared with Cu (II), As (V) exposure led to the insignificant downregulation of a variety of biosynthesis processes, which would be one possible account for the less inhibited activity. More importantly, the inhibited mechanisms on the organohalide respiration catabolism of strain CP-1 were firstly revealed. Cu (II) stress severely downregulated NADH generation during TCA cycle and electron donation of organohalide respiration process, which might decrease the reducing power required for organohalide respiration. While both Cu (II) and As (Ⅴ) inhibited substrate level phosphorylation during TCA cycle, as well as electron transfer and ATP generation during organohalide respiration. Meanwhile, CprA-2 was confirmed as the responsible reductive dehalogenase in charge of 2,4,6-TCP dechlorination, and transcriptional and proteomic studies confirmed the directly inhibited gene transcription and expression of CprA-2. The in-depth reveal of inhibitory effects and mechanism gave theoretical supports for alleviating heavy metal inhibition on organohalide respiration activity in groundwater co-contaminated with organohalides and heavy metals.

Exploring the bioremediation capability of petroleum-contaminated soils for enhanced environmental sustainability and minimization of ecotoxicological concerns

The bioremediation of soils contaminated with petroleum hydrocarbons (PHCs) has emerged as a promising approach, with its effectiveness contingent upon various types of PHCs, i.e., crude oil, diesel, gasoline, and other petroleum products. Strategies like genetically modified microorganisms, nanotechnology, and bioaugmentation hold potential for enhancing remediation of polycyclic aromatic hydrocarbon (PAH) contamination. The effectiveness of bioremediation relies on factors such as metabolite toxicity, microbial competition, and environmental conditions. Aerobic degradation involves enzymatic oxidative reactions, while bacterial anaerobic degradation employs reductive reactions with alternative electron acceptors. Algae employ monooxygenase and dioxygenase enzymes, breaking down PAHs through biodegradation and bioaccumulation, yielding hydroxylated and dihydroxylated intermediates. Fungi contribute via mycoremediation, using co-metabolism and monooxygenase enzymes to produce CO2 and oxidized products. Ligninolytic fungi transform PAHs into water-soluble compounds, while non-ligninolytic fungi oxidize PAHs into arene oxides and phenols. Certain fungi produce biosurfactants enhancing degradation of less soluble, high molecular-weight PAHs. Successful bioremediation offers sustainable solutions to mitigate petroleum spills and environmental impacts. Monitoring and assessing strategy effectiveness are vital for optimizing biodegradation in petroleum-contaminated soils. This review presents insights and challenges in bioremediation, focusing on arable land safety and ecotoxicological concerns.

Speciation and transformation of nitrogen for swine manure thermochemical liquefaction

The nitrogen conversion mechanism of swine manure by thermochemical liquefaction with ethanol as solvent was investigated at a lower temperature range (180–300 °C). The fate of nitrogen in liquid phase products, bio-oil and biochar was evaluated by XPS, GC–MS and other methods. After thermochemical liquefaction, most of the nitrogen in swine manure was transferred to biochar (63.75%). As the temperature increased to 220 °C, the biochar-N yields decreased to 43.29%, accompanied by an increase in bio-oil-N and liquid phase product-N by 7.99% and 1.26% respectively. The results indicated that increasing the temperature could facilitate solid nitrogen structure cracking into bio-oil-N. Amines and heterocyclic nitrogen from protein peptide bond cracking and Maillard reactions made up the main nitrogen compounds in bio-oil, and high temperatures favored the further cyclization and condensation of heterocyclic nitrogen (e.g., indole, quinoline). In the case of biochar, the inorganic nitrogen disappeared at 260 °C and was obviously transformed into liquid phase products. The rising temperature promoted the polymerization of pyridine nitrogen and pyrrole nitrogen, which formed more stabilized nitrogen formation (such as quaternary nitrogen). Nitrogen conversion and possible reaction schematics during swine manure thermochemical liquefaction were explored in this study.

Study on the Bacterial Communities of the Biofilms on Titanium, Aluminum, and Copper Alloys at 5,772 m Undersea in Yap Trench

Biofilms formed on metal surfaces strongly affect metallic instruments serving in marine environments. However, due to sampling difficulty, less has been known about the bacterial communities of the biofilm on metallic surfaces in hadal environments, so the failure process of these deep-sea metallic instruments influenced by microbial communities could be hardly predicted. In this research, seven alloys, including titanium, aluminum, and copper alloys, were exposed in Yap Trench hadal environment for 1 year. Thus, the communities of the biofilms formed on metallic surfaces at 5,772 m undersea in Yap Trench were initially reported in previous studies. Then, 16S rRNA gene sequencing was performed to visualize the in situ bacterial communities of the biofilms formed on titanium, aluminum, and copper alloys at 5,772 m undersea in Yap Trench. It was found that Proteobacteria was the dominant phylum in all samples, but distinct genera were discovered on various alloys. The titanium alloy provided a suitable substrate for a mutualistic symbiotic biofilm with abundant bacterial richness. Aluminum alloys without copper components showed the least bacterial richness and formed a cold-adapted and oligotrophic-adapted biofilm containing the genera Sulfurimonas and PS1 Clade, while copper-present alloys showed relatively high bacterial richness with copper-resistant or even copper-utilizing biofilms constituting the genera Stenotrophomonas, Burkholderia-Caballeronia-Paraburkholderia, and Achromobacter on the surfaces. Furthermore, among all the element components contained in alloys investigated in this research, copper element showed the strongest influences on the composition and function of microbial communities in the biofilms formed on various metallic surfaces.

Removal of sulfamethazine and Cu2+ by Sakaguchia cladiensis A5: Performance and transcriptome analysis

To reduce the potential risks of contamination of antibiotics and heavy metals to ecological environment and human safety, biological removal of these composite pollutants is the focus of much study. One previously identified isolate, Sakaguchia cladiensis A5, was used to decompose sulfamethazine (SMZ) and adsorb Cu²⁺. The ability of A5 to remove SMZ was enhanced by pre-induced culture, which reached 49.8% on day 9. The removal of SMZ could be also increased to 37.6% on day 3 in the presence of Cu²⁺, but only to 12.2% in the system without Cu²⁺. The biosorption of Cu²⁺ mainly occurred on the cell walls, while the biodegradation of SMZ was inside the cells. By comparative transcriptome analysis for A5, 1270 and 2220 differentially expressed genes (DEGs) were identified after treating single SMZ and SMZ/Cu²⁺, respectively. The Gene expression pattern analysis suggested a suppression of transcriptional changes in A5 responding to SMZ/Cu²⁺ as compared to under the sole stress of SMZ. The DEGs functional enrichment analysis suggested that the antioxidant and sulfate assimilation pathways played a key role on SMZ biodegradation and Cu²⁺ biosorption. The DEGs of proteins CAT, PRDX5, SAT, and CYSC were up-regulated to facilitate the resistance of A5 against oxidative toxicity of Cu²⁺. Moreover, the protein MET30 activated by Cu²⁺ was also overexpressed to promote the transmembrane transport of SMZ, such that A5 could decompose SMZ more effectively in SMZ/Cu²⁺ system. The results of this study would provide new insights into the mechanism of biodegradation and biosorption of SMZ/Cu²⁺.

Effects of benzo [a] pyrene (BaP) on the composting and microbial community of sewage sludge

Benzo [a] pyrene (BaP), the most ubiquitous polycyclic aromatic hydrocarbons (PAHs) found in sludge, can impact the composting processes of sewage sludge as well as the quality of compost produced. In the present study, we investigated the effects of BaP at various concentrations on physicochemical characteristics, heavy metal passivation, and microbial community during the composting processes. The removal efficiency of BaP at 5 and 20 mg kg^-1 after composting was 51.1% and 74.2%, respectively. In comparison with the control, the content of residual Cu, Pb, Cr and Ni in 5 mg kg^-1 BaP contained system declined dramatically on the second day of composting, while such content in 20 mg kg^-1 BaP system significantly decreased on the 8th day. Regardless of the presence of BaP in the sludge, composting process had a positive passivation effect on Cu, Pb, Cr and Ni. A stronger inhibitory effect of BaP at higher concentration was observed on microorganism, which reduced microbial abundance and species in the composting, and influenced microbial diversity. Besides, microbial communities in BaP-containing composting would improve the transformation of silicates and minerals, increase the concentration of humus and extend the passivation time of heavy metals. As these results verified, composting process could remove BaP from the sludge effectively, and BaP had a significant impact on heavy metal passivation and abundance and composition of microbial community during the composting process.

Aerobic denitrification by Paracoccus sp. YF1 in the presence of Cu(II)

This study of Cu(II)'s impact on aerobic denitrification of Paracoccus sp. YF1 revealed that the denitrification rate decreased markedly from 99.8%, 98.0%, 68.7% to 16.3% when the concentrations of Cu(II) rose from 0, 0.01 mM, 0.05 mM to 0.1 mM, respectively. This outcome was confirmed by the successful test of OD₆₀₀, total protein and enzyme activities. As the concentration of Cu(II) increased from 0 to 0.1 mM, the total protein contents declined over a period of 48 h, and the activities of nitrate reductase (NR) and nitrite reductase (NIR) decreased remarkably during the first 24 h in a NO₃^- sufficient state. Meanwhile, the reduction of NO₃^- and NO₂^- was positively correlated with the expression level of NR and NIR. The removal rate of nitrate in the control treatment and different concentration of Cu(II) treatment fitted approximately to the zero-order model. Scanning electron microscopy (SEM) confirmed that the cell surfaces of Paracoccus sp. YF1 were disrupted when exposed to 0.1 mM Cu(II). The adsorption of Cu(II) onto the cells' surface was confirmed by Energy dispersive spectrometer (EDS), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy analysis (XPS). The insights obtained here regarding the influence of Cu(II) on aerobic denitrification will be of great significance for the treatment of heavy metals and nitrite co-existing sewage.

UV-B radiation induces DEHP degradation and their combined toxicological effects on Scenedesmus acuminatus

The co-contamination discharge of Phthalate esters (PAEs) by human activities and the increased UV radiation is increasing in aquatic ecosystems. However, little information is available about the combined detrimental effects of UV and PAEs on phytoplankton. In this study, the combined effects of UV-B irradiation and di-(2-ethylhexyl) phthalate (DEHP) on photosynthesis and antioxidant system of Scenedesmus acuminatus, and the DEHP degradation were investigated. Results showed that UV-B radiation decreased the chlorophyll a fluorescence yield, photosynthetic activity (Fv/Fm), pigment content and superoxide dismutase activity. This radiation also increased the reactive oxygen species (ROS) production and soluble protein and malondialdehyde contents. UV-B radiation with 10 mg L^-1 DEHP improved the Fv/Fm and alleviated the cell damage of S. acuminatus, and the addition of high DEHP concentration (≥50 mg L^-1) aggravated cell damage. The ROS generation also decreased with the increased DEHP concentration. UV-B radiation can effectively promote the DEHP degradation, with the highest degradation rate of 89.9% at an initial DEHP concentration of 10 mg L^-1 within 6 h. This result may be attributed to that UV-B irradiance induced DEHP degradation under the regulation of ROS generated by S. acuminatus. Our findings will contribute to the understanding of the combined toxic mechanisms of UV-B and DEHP and in the evaluation of ecological environment risks for primary producers in aquatic ecosystems.

Electrochemical and microbial community responses of electrochemically active biofilms to copper ions in bioelectrochemical systems

Heavy metals play an important role in the conductivity of solution, power generation and activity of microorganisms in bioelectrochemical systems (BESs). However, effect of heavy metal on the process of exoelectrogenesis metabolism and extracellular electron transfer of electrochemically active biofilms (EABs) was poorly understood. Herein, we investigated the impact of Cu²⁺ at gradually increasing concentration on the morphological and electrochemical performance and bacterial communities of anodic biofilms in mixed-culture BESs. The voltage output decreased continuously and dropped to zero at 10 mg L^-1, which was attributed to the toxic inhibition that cased anodic biofilm damage and decreased secretion of outer membrane cytochromes. When stopping the introduction of Cu²⁺ to anodic chamber, the maximum voltage production recovered 75.1% of the voltage produced from BES and coulombic efficiency was higher but acetate removal rate was lower than that before Cu²⁺ addition, demonstrating the recovery capability of EABs was higher compared to nonelectroactive bacteria. Moreover, SEM-EDS and XPS suggested that most of Cu²⁺ was adsorbed by the anode electrode and reduced by EABs on anode. Compared to the open-circuit BES, the flow of electrons through a circuit could improve the reduction of copper. Community analysis showed a decrease in Geobacter accompanied by an increase in Stenotrophomonas in response to Cu²⁺ shock in anodic chamber.

Anaerobic biodegradation of benzo(a)pyrene by a novel Cellulosimicrobium cellulans CWS2 isolated from polycyclic aromatic hydrocarbon-contaminated soil

Cellulosimicrobium cellulans CWS2, a novel strain capable of utilizing benzo(a)pyrene (BaP) as the sole carbon and energy source under nitrate-reducing conditions, was isolated from PAH-contaminated soil. Temperature and pH significantly affected BaP biodegradation, and the strain exhibited enhanced biodegradation ability at temperatures above 30 °C and between pH 7 and 10. The highest BaP removal rate (78.8%) was observed in 13 days when the initial BaP concentration was 10 mg/L, and the strain degraded BaP at constant rate even at a higher concentration (50 mg/L). Metal exposure experimental results illustrated that Cd(II) was the only metal ion that significantly inhibited biodegradation of BaP. The addition of 0.5 and 1.0 g/L glucose enhanced BaP biodegradation, while the addition of low-molecular-weight organic acids with stronger acidity reduced BaP removal rates during co-metabolic biodegradation. The addition of phenanthrene and pyrene, which were degraded to some extent by the strain, showed no distinct effect on BaP biodegradation. Gas chromatography–mass spectrometry (GC-MS) analysis revealed that the five rings of BaP opened, producing compounds with one to four rings which were more bioavailable. Thus, the strain exhibited strong BaP degradation capability and has great potential in the remediation of BaP-/PAH-contaminated environments.

Biodegradation of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) by Phanerochaete chrysosporium in the presence of Cd2

Aerobic biodegradation of 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47) by Phanerochaete chrysosporium in the presence of Cd²⁺ was investigated in this study. The results showed that P. chrysosporium could effectively degrade BDE-47, and its extracellular enzyme played an important role in the process of decomposition. BDE-47 biodegradation by fungi was more tolerant than extracellular enzyme in the presence of Cd²⁺. Also, both of the activity of two typical enzymes, MnP and LiP, descended with ascended Cd²⁺ concentration. Based on the four mono-hydroxylated PBDEs (5-OH-BDE-47, 4'-OH-BDE-17, 6-OH-BDE-47, and 2'-OH-BDE-28) and two bromophenols (2,4-DBP, 4-BP) detected, three possible degradation pathways were proposed, inferring that BDE-47 was more easily to transform via hydroxylation. With addition of Cd²⁺, the types of degradation products did not change, merely a variation of the content of these products observed. Meanwhile, the major metabolites of BDE-47, bromophenol compounds, have been found to be transformed or even mineralized by P. chrysosporium quickly, which also helped better explain why the amounts of BDE-47 decomposed did not match with that of the metabolites detected.

Physiology and bioprocess of single cell of Stenotrophomonas maltophilia in bioremediation of co-existed benzo[a]pyrene and copper

Polycyclic aromatic hydrocarbons (PAHs) and heavy metals are generally present in mixtures in the e-waste dismantling areas, posing serious health risk to the local people. Bioremediation has been considered as a promising approach for PAHs and heavy metals removal. In this study, we applied flow cytometry to obtain a better understanding of membrane potential (MP), apoptosis and cell cycle of Stenotrophomonas maltophilia affected by combined pollutants of benzo[a]pyrene(BaP) and Cu(II). The results showed that BaP was the main factor damaging the cell membrane and influencing the MP. S. maltophilia could even protect against upsetting situation by encouraging early apoptosis, whereby compromised cells committed suicide, as a result, which, in turn, facilitated the metabolism of the bacteria with high-vitality. Furthermore, even if the bacterial cell division was blocked and stopped reproduction, a large number of key enzymes inside cells could still be used for degradation of BaP. The expression of protein related to the transport and metabolism of BaP, regulation of redox reactions and phosphorylation in bacterial cell during bioprocess were evident different.