Structure and function of the bacterial communities during rhizoremediation of hexachlorobenzene in constructed wetlands

Plant and microbial communities responded to copper and/or tetracyclines in mycorrhizal enhanced vertical flow constructed wetlands microcosms with Canna indica L

Arbuscular mycorrhizal fungi (AMF) play a significant role in pollutants removal in constructed wetlands (CWs). However, the purification effects of AMF on combined copper (Cu) and tetracycline (TC) pollution in CWs remains unknown. This study investigated the growth, physiological characteristics and AMF colonization of Canna indica L. living in vertical flow CWs (VFCWs) treated for Cu and/or TC pollution, the purification effects of AMF enhanced VFCWs on Cu and TC, and the microbial community structures. The results showed that (1) Cu and TC inhibited plant growth and decreased AMF colonization; (2) the removal rates of TC and Cu by VFCWs were 99.13-99.80% and 93.17-99.64%, respectively; (3) the growth, Cu and TC uptakes of C. indica and Cu removal rates were enhanced by AMF inoculation; (4) TC and Cu stresses reduced and AMF inoculation increased bacterial operational taxonomic units (OTUs) in the VFCWs, Proteobacteria, Bacteroidetes, Firmicutes and Acidobacteria were the dominant bacteria, and AMF inoculation decreased the relative abundance of Novosphingobium and Cupriavidus. Therefore, AMF could enhance the pollutants purification in VFCWs by promoting plant growth and altering the microbial community structures.

Possible Processes and Mechanisms of Hexachlorobenzene Decomposition by the Selected Comamonas testosteroni Bacterial Strains

Background: The bacterial destructing activity toward pesticides has been the focus of research in the last few decades. Hexachlorobenzene is included in the organochlorine pesticides group that are prohibited for use. However, large hexachlorobenzene amounts are still concentrated in the soil, stressing the relevance of research on hexachlorobenzene-destroying bacteria. Methods: The ability to destroy hexachlorobenzene by Comamonas testosteroni UCM B-400, B-401, B-213 strains was investigated and established. Bacteria were cultivated (7 days at 28 °C) in mineral Luria-Bertrani (LB) medium with three hexachlorobenzene doses: 10, 20, 50 mg/L. The hexachlorobenzene concentrations were recorded by a gas chromatography method. Results: The results showed that C. testosteroni UCM B-400, B-401 have high destructive activity toward hexachlorobenzene. The highest (50 mg/L) initial concentration decreased to 41.5 and 43.8%, respectively, for C. testosteroni UCM B-400, B-401. The unadapted C. testosteroni UCM B-213 was tolerant to hexachlorobenzene (cell titers after cultivating with 10.0, 20.0, 50.0 mg/mL were higher compared to initial titer), but had a low-destructing activity level (two times less than B-400 and B-401). Conclusions: Bacterial strains C. testosteroni UCM B-400, B-401 can be seen as a potential soil bioremediation from hexachlorobenzene pollution.

Molecular Research of Lipid Peroxidation and Antioxidant Enzyme Activity of Comamonas testosteroni Bacterial Cells under the Hexachlorobenzene Impact

The species of Comamonas testosteroni is the most common human pathogen of the genus, which can be associated with acute appendicitis, infections of the bloodstream, the peritoneal cavity, cerebrospinal fluid, inflammatory bowel disease, and in general, bacteremia. According to the literature, Comamonas testosteroni has destructive activity to a wide range of toxic chemical compounds, including chlorobenzenes. The specified strains were isolated from the soil of the organochlorine waste landfill, where hexachlorobenzene (HCB) was predominant. These strains were expected to be capable of degrading HCB. Microbiological (bacterial enrichment and cultivating, bacterial biomass obtaining), molecular biology, biochemical (enzymatic activities, malondialdehyde measuring, peroxidation lipid products measuring), and statistical methods were carried out in this research. The reaction of both strains (UCM B-400 and UCM B-401) to the hexachlorobenzene presence differed in the content of diene and triene conjugates and malondialdehyde, as well as different catalase and peroxidase activity levels. In terms of primary peroxidation products, diene conjugates were lower, except conditions with 20 mg/L HCB, where these were higher up to two times, than the pure control. Malondialdehyde in strain B-400 cells decreased up to five times, in B-401, but increased up to two times, compared to the pure control. Schiff bases in strain B-400 cells were 2–3 times lower than the pure control. However, in B-401 cells Schiff bases under higher HCB dose were in the same level with the pure control. Catalase activity was 1.5 times higher in all experimental variants, compared to the pure control (in the strain B-401 cells), but in the B-400 strain, cells were 2 times lower, compared to the pure control. The response of the two strains to hexachlorobenzene was similar only in peroxidase activity terms, which was slightly higher compared to the pure control. The physiological response of Comamonas testosteroni strains to hexachlorobenzene has a typical strain reaction. The physiological response level of these strains to hexachlorobenzene confirms its tolerance, and indirectly, the ability to destroy the specified toxic compound.

Biochemical and Metabolic Plant Responses toward Polycyclic Aromatic Hydrocarbons and Heavy Metals Present in Atmospheric Pollution

Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) are toxic components of atmospheric particles. These pollutants induce a wide variety of responses in plants, leading to tolerance or toxicity. Their effects on plants depend on many different environmental conditions, not only the type and concentration of contaminant, temperature or soil pH, but also on the physiological or genetic status of the plant. The main detoxification process in plants is the accumulation of the contaminant in vacuoles or cell walls. PAHs are normally transformed by enzymatic plant machinery prior to conjugation and immobilization; heavy metals are frequently chelated by some molecules, with glutathione, phytochelatins and metallothioneins being the main players in heavy metal detoxification. Besides these detoxification mechanisms, the presence of contaminants leads to the production of the reactive oxygen species (ROS) and the dynamic of ROS production and detoxification renders different outcomes in different scenarios, from cellular death to the induction of stress resistances. ROS responses have been extensively studied; the complexity of the ROS response and the subsequent cascade of effects on phytohormones and metabolic changes, which depend on local concentrations in different organelles and on the lifetime of each ROS species, allow the plant to modulate its responses to different environmental clues. Basic knowledge of plant responses toward pollutants is key to improving phytoremediation technologies.

Spatial-Temporal Changes in Removal of Fecal Indicators and Diversity of Bacterial Communities in a Constructed Wetland with Ornamental Plants

The present study was undertaken in a constructed wetland (CW), setup in a tourism house, for domestic wastewater treatment. The influence of season variations on the abundance of fecal indicator organisms (total coliforms and Escherichia coli) in the wastewater and in the substrate and the roots of plants inhabiting the inlet and outlet zones of the CW was evaluated along three consecutive years. The structure and diversity of bacterial communities associated to the CW’s substrate of inlet and outlet zones was also analyzed overtime. Wastewater was characterized for physicochemical and microbiological parameters and the bacterial communities colonizing the substrate surface, were analyzed by Denaturing Gradient Gel Electrophoresis (DGGE). The CW was effective in removing COD, BOD5, TSS, PO43−, NH4+, NO3−, and NO2−. It was also effective in removing fecal indicators, with a generalized decrease of total coliforms and E. coli in the substrate and in the wastewater from inlet to outlet of up to 2–3 log. The structure and composition of bacterial communities associated with the substrate was mainly influenced by the year rather than by the season or the CW zone.

Temporal Evolution of Bacterial Endophytes Associated to the Roots of Phragmites australis Exploited in Phytodepuration of Wastewater

Improvement of industrial productions through more environment-friendly processes is a hot topic. In particular, land and marine environment pollution is a main concern, considering that recalcitrant compounds can be spread and persist for a long time. In this context, an efficient and cost-effective treatment of wastewater derived from industrial applications is crucial. Phytodepuration has been considered as a possible solution and it is based on the use of plants and their associated microorganisms to remove and/or transform pollutants. In this work we investigated the culturable microbiota of Phragmites australis roots, sampled from the constructed wetlands (CWs) pilot plant in the G.I.D.A. SpA wastewater treatment plant (WWTP) of Calice (Prato, Tuscany, Italy) before and after the CW activation in order to check how the influx of wastewater might affect the resident bacterial community. P. australis specimens were sampled and a panel of 294 culturable bacteria were isolated and characterized. This allowed to identify the dynamics of the microbiota composition triggered by the presence of wastewater. 27 out of 37 bacterial genera detected were exclusively associated to wastewater, and Pseudomonas was constantly the most represented genus. Moreover, isolates were assayed for their resistance against eight different antibiotics and synthetic wastewater (SWW). Data obtained revealed the presence of resistant phenotypes, including multi-drug resistant bacteria, and a general trend regarding the temporal evolution of resistance patterns: indeed, a direct correlation linking the appearance of antibiotic- and SWW-resistance with the time of exposure to wastewater was observed. In particular, nine isolates showed an interesting behavior since their growth was positively affected by the highest concentrations of SWW. Noteworthy, this study is among the few investigating the P. australis microbiota prior to the plant activation.

Sub-Lethal Effects of Pesticides on the DNA of Soil Organisms as Early Ecotoxicological Biomarkers

This review describes the researches performed in the last years to assess the impact of pesticide sub-lethal doses on soil microorganisms and non-target organisms in agricultural soil ecosystems. The overview was developed through the careful description and a critical analysis of three methodologies based on culture-independent approaches involving DNA extraction and sequencing (denaturing gradient gel electrophoresis, DGGE; next-generation sequencing, NGS) to characterize the microbial population and DNA damage assessment (comet assay) to determine the effect on soil invertebrates. The examination of the related published articles showed a continuous improvement of the possibility to detect the detrimental effect of the pesticides on soil microorganisms and non-target organisms at sub-lethal doses, i.e., doses which have no lethal effect on the organisms. Considering the overall critical discussion on microbial soil monitoring in the function of pesticide treatments, we can confirm the usefulness of PCR-DGGE as a screening technique to assess the genetic diversity of microbial communities. Nowadays, DGGE remains a preliminary technique to highlight rapidly the main differences in microbial community composition, which is able to give further information if coupled with culture-dependent microbiological approaches, while thorough assessments must be gained by high-throughput techniques such as NGS. The comet assay represents an elective technique for assessing genotoxicity in environmental biomonitoring, being mature after decades of implementation and widely used worldwide for its direct, simple, and affordable implementation. Nonetheless, in order to promote the consistency and reliability of results, regulatory bodies should provide guidelines on the optimal use of this tool, strongly indicating the most reliable indicators of DNA damage. This review may help the European Regulation Authority in deriving new ecotoxicological endpoints to be included in the Registration Procedure of new pesticides.

Evaluation of the fate of nutrients, antibiotics, and antibiotic resistance genes in sludge treatment wetlands

The aim of this research was to analyze the elimination of nutrients, antibiotics as well as antibiotic resistance genes (ARGs) in different sludge treatment wetlands (STWs) with or without reeds and aeration tubes. Five antibiotics, including oxytetracycline, tetracycline, azithromycin, sulfamethoxazole, and sulfadiazine; five ARGs, including two tetracycline ARGs (tetC and tetA), one macrolide ARGs (ermB), and two sulfonamide ARGs (sul1 and sul2); and one integrase gene (intI1) were determined in the surface and bottom layers of three STWs, respectively. The removal efficiencies of antibiotics in the bottom layer were lower than that in the surface layer, while the elimination efficiencies of ARGs showed opposite trend. Strong correlations were observed among the contents of antibiotics as well as related ARGs, and the abundance of ARGs had a strong correlation with intI1. The results demonstrated that the contents of these pollutants decreased during the resting period in all the STWs, while the wetland had reeds and aeration tubes performed the best.

Rhizodegradation of Petroleum Oily Sludge-contaminated Soil Using Cajanus cajan Increases the Diversity of Soil Microbial Community

Most components of petroleum oily sludge (POS) are toxic, mutagenic and cancer-causing. Often bioremediation using microorganisms is hindered by the toxicity of POS. Under this circumstance, phytoremediation is the main option as it can overcome the toxicity of POS. Cajanus cajan a legume plant, was evaluated as a phyto-remediating agent for petroleum oily sludge-spiked soil. Culture dependent and independent methods were used to determine the rhizosphere microorganisms' composition. Degradation rates were estimated gravimetrically. The population of total heterotrophic bacteria (THRB) was significantly higher in the uncontaminated soil compared to the contaminated rhizosphere soil with C. cajan, but the population of hydrocarbon-utilizing bacteria (HUB) was higher in the contaminated rhizosphere soil. The results show that for 1 to 3% oily sludge concentrations, an increase in microbial counts for all treatments from day 0 to 90 d was observed with the contaminated rhizosphere CR showing the highest significant increase (p  < 0.05) in microbial counts compared to other treatments. The metagenomic study focused on the POS of 3% (w/w) and based on the calculated bacterial community abundance indices showed an increase in the values for Ace, Cho, Shannon (Shannon-Weaver) and the Simpson's (measured as InvSimpson) indices in CR3 compared to CN3. Both the Simpson's and the Shannon values for CR3 were higher than CN3 indicating an increase in diversity upon the introduction of C. cajan into the contaminated soil. The PCoA plot revealed community-level differences between the contaminated non-rhizosphere control and contaminated rhizosphere microbiota. The PCoA differentiated the two treatments based on the presence or absence of plant. The composition and taxonomic analysis of microbiota-amplified sequences were categorized into eight phyla for the contaminated non-rhizosphere and ten phyla for the contaminated rhizosphere. The overall bacterial composition of the two treatments varied, as the distribution shows a similar variation between the two treatments in the phylum distribution. The percentage removal of total petroleum hydrocarbon (TPH) after 90 days of treatments with 1, 2, 3, 4, and 5% (w/w) of POS were 92, 90, 89, 68.3 and 47.3%, respectively, indicating removal inhibition at higher POS concentrations. As the search for more eco-friendly and sustainable remediating green plant continues, C. cajan shows great potential in reclaiming POS contaminated soil. Our findings will provide solutions to POS polluted soils and subsequent re-vegetation.

Fate of antibiotics in three distinct sludge treatment wetlands under different operating conditions

Sludge treatment wetlands (STWs) have recently been used to treat surplus sludge. However, the distribution of antibiotics involved in the process has not been comprehensively investigated. This study aimed to evaluate the fate of two antibiotics, i.e., ciprofloxacin (CIP) and azithromycin (AZM) in STWs during the treatment of surplus sludge. Three pilot-scale STWs units-S1 with aeration tubes, S2 with aeration tubes and reed planting, and S3 with reed planting-were constructed and operated under feeding followed by resting periods. The results showed that antibiotic content in residual sludge decreased over time and unit S2 performed the best in terms of antibiotic removal. Planting reed considerably improved the antibiotic removal performance of the STWs. Biodegradation and absorption resulted in removal of most of the antibiotics in the test units. Less than 2% of the antibiotics was taken up by plants, whereas <5% of the influent antibiotics left the STW units through the drainage discharge. Overall, STW units contributed to effectively decrease CIP and AZM to 41-72% and 49-84%, respectively.

Seasonal dynamics of bacterial communities associated with antibiotic removal and sludge stabilization in three different sludge treatment wetlands

In this study, antibiotics removal, sludge stabilization and the change in the bacterial community in sludge treatment wetlands (STWs) were investigated in different seasons. Pilot-scale STWs were characterized for sludge stabilization and the fate of antibiotics in surplus sludge applied during different seasons in three different configurations. The three configurations were unit S1 with ventilation, unit S2 with ventilation and reed plantings and unit S3 with reed plantings. The antibiotics used were ciprofloxacin, azithromycin and oxytetracycline and their degradation, degree of sludge stabilization and bacterial community dynamics were monitored. The results showed that the removal of antibiotics and reduction in the amount of organics in the planted units S2 and S3 were higher than those in the unplanted unit S1, especially in summer. The antibiotic removal efficiency in the planted unit S2, which was equipped with aeration tubes, was the highest over the entire test period. Bacterial community was analyzed by IlluminaMiSeq sequencing of the 16SrRNA gene, showed that the presence of plants in STWs enhanced microbial diversity and richness which promote the removal of antibiotics and sludge stabilization. Proteobacteria, Bacteroidetes and Firmicutes were dominant in the bacterial communities, with Thiobacillus, Dechloromonas and Pseudomonas occurring as dominant genera.

Application of common duckweed (Lemna minor) in phytoremediation of chemicals in the environment: State and future perspective

Over the past 50 years, different strategies have been developed for the remediation of polluted air, land and water. Driven by public opinion and regulatory bottlenecks, ecological based strategies are preferable than conventional methods in the treatments of chemical effluents. Ecological systems with the application of microbes, fungi, earthworms, plants, enzymes, electrode and nanoparticles have been applied to varying degrees in different media for the remediation of various categories of pollutants. Aquatic macrophytes have been used extensively for the remediation of pollutants in wastewater effluents and aquatic environment over the past 30 years with the common duckweed (L. minor) as one of the most effective macrophytes that have been applied for remediation studies. Duckweed has shown strong potentials for the phytoremediation of organic pollutants, heavy metals, agrochemicals, pharmaceuticals and personal care products, radioactive waste, nanomaterials, petroleum hydrocarbons, dyes, toxins, and related pollutants. This review covers the state of duckweed application for the remediation of diverse aquatic pollutants and identifies gaps that are necessary for further studies as we find pragmatic and sound ecological solutions for the remediation of polluted environment for sustainable development.