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Microbial consortia-mediated biodegradation of 1,4-dioxane (1,4-D), an emerging water contaminant, is always a superior choice over axenic cultures. Thus, better understanding of the functions of coexisting microbes and their interspecies interactions within the consortia is crucial for predicting biodegradation efficiency and designing efficient 1,4-D-degrading microbial consortia. This study evaluated how microbial community compositions and interspecies interactions govern the microbial consortia-mediated 1,4-D biodegradation by investigating the biodegradability and microbial community dynamics of both enriched (N112) and synthetic (SCDs and SCDNs) microbial consortia in the absence or presence of additional organic compound (AOC). In the absence of AOC, N112 exhibited 100% 1,4-D biodegradation efficiency at a rate of 12.5 mg/L/d, whereas the co-occurrence of AOC resulted in substrate-dependent biodegradation inhibition and thereby reduced the biodegradation efficiency and activity (2.0-10.0 mg/L/d). The coexistence and negative influence of certain low-abundant non-degraders on both 1,4-D-degraders and key non-degraders in N112 was identified as the prime cause behind such biodegradation inhibition. Comparing with N112, SCDN-1 composed of 1,4-D-degraders and key non-degraders significantly improved the 1,4-D biodegradation efficiency in the presence of AOC, confirming the absence of negative influence of low-abundant non-degraders and cooperative interactions between 1,4-D-degraders and key non-degraders in SCDN-1. On the contrary, both two-species and three-species SCDs comprised of only 1,4-D-degraders resulted in lower 1,4-D biodegradation efficiency as compared to SCDN-1 under all treatment conditions, while max. 91% 1,4-D biodegradation occurred by SCDs in the absence of AOC. These results were attributed to the negative interaction among 1,4-D-degraders and the absence of complementary roles of key non-degraders in SCDs. The findings improve our understanding of how interspecies interactions can regulate the intrinsic abilities and functions of coexisting microbes during biodegradation in complex environments and provide valuable guidelines for designing highly efficient and robust microbial consortia for practical bioremediation of 1,4-D like emerging organic contaminants.

Arabidopsis halleri ssp. gemmifera is classified as Cd and Zn hyperaccumulator plant, however, the disparity accumulation preferences in organs (root, stem and leaves) between cadmium and zinc seems less understandable. Therefore, this study aimed to portray accumulation behaviour toward the presence of Cd and Zn in the hydroponic method employing A. halleri ssp. gemmifera. The experiment was conducted by applying this plant using 2 and 300 µM of Cd, and 2 and 200 µM Zn, together with 20% Hoagland solution for 7 days, separately. The results showed that Zn in the medium was uptake faster than Cd. Furthermore, increasing Cd/Zn supply at the medium resulted in an increasing accumulation of Cd/Zn in the organs of the plant. In both Cd treatments, the accumulation followed the order of stem>root>leaves, indicating Cd transportation to the upper part has occurred during this period. The same accumulation preference pattern was also reported in the 200 µM Zn supply. However, at 2 µM Zn supply, Zn accumulation was mainly found in the leaves, followed by the root and stem. A. halleri ssp. gemmifera uptake Zn faster from the medium and translocate rapidly to the leaves at low-level Zn supply. Increasing Zn supply concentration might inhibit the translocation of Zn from stem to leaves. Meanwhile, regardless of Cd supply concentrations, this plant could only translocate Cd to the stem mostly within a short-time exposure period. Therefore, this study concluded that A. halleri ssp. gemmifera exhibited different accumulation responses when exposed to different Cd and Zn supply concentrations.

This study focuses on how to solve cadmium (Cd) contamination in soil because this contaminant decreases soil quality. Soil remediation using the hyperaccumulator plants is an optional process to solve soil contamination. Arabidopsis halleri ssp. gemmifera (hereinafter referred to as A. halleri), is one of the candidate plants expected to be used for phytoremediation of Cd contaminated soil. The A. halleri promote solubilization of Cd in the soil directly or indirectly using its secreted root exudate. However, the effect of the metabolites profile of this plant to Cd uptake from contaminated soil is still unclear. The purpose of this study is to examine the contribution of root exudates of A. halleri to extract Cd in the soil. Cd-contaminated soil used in this study was a farmland soil containing 5.8 mg kg-1 of Cd and 648 mg kg-1 of Zn taken from Tome City, Miyagi Prefecture, Japan. Soil leaching tests were conducted using the solution containing the root exudates from A. halleri plant. The accelerating effect of root exudates of A. halleri on solubilization of Cd is fundamental information to construct the benefit of phytoremediation.

In this study, the phytoremediation potential of tropical and subtropical arsenic (As) hyperaccumulating fern Pteris vittata in an As contaminated farmland field near an abandoned goldmine was investigated. The tested field is located in a subarctic area of northeast Japan. This study was aimed at decreasing the risk of As in the soil (water-soluble As) with nurturing the soil and respecting the plant life cycle for the sustainable phytoremediation for 8 years. The field was tilled and planted with new seedlings of the fern every spring and the grown fern was harvested every autumn. The biomass and As concentration in fronds, rhizomes and roots of the fern were analyzed separately after harvesting each year. The biomass of the fronds of P. vittata was significantly affected by the yearly change of the weather condition, but As concentration in fronds was kept at 100-150 mg/kg dry weight. The accumulated As in P. vittata was higher than that of As-hyperaccumulator fern Pteris cretica, the native fern in the field trial area. Harvested biomass of P. vittata per plant was also higher than that of P. cretica. More than 43.5 g As/154 m

Grasses are advantageous in the removal of polycyclic aromatic hydrocarbons (PAHs) in soil because of their fibrous root, high tolerance to environmental stress, and low nutritional requirements. In this study, a pot experiment was conducted to test the ability of four grasses to remove PAHs in the soil, and to investigate the corresponding bacterial community shift in the rhizosphere of each. Sudangrass achieved the maximum removal of PAHs at 98% dissipation rate after 20 days. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and next-generation sequencing revealed that sudangrass specially enriched the growth of a known PAHs degrader, Sphingomonadales, regardless of the presence or absence of PAHs in the soil. Moreover, the gene copy numbers of PAHs catabolic genes, PAH-RHDα and nidA, as measured by real time-PCR (RT-PCR) were highest in the soil planted with sudangrass. Overall, this study suggested that sudangrass further enhanced the dissipation of PAHs by enriching Sphingomonadales in its rhizosphere.

Phytoremediation is a promising inexpensive method of detoxifying arsenic (As) contaminated soils using plants and associated soil microorganisms. The potential of Pteris vittata to hyperaccumulate As contamination has been investigated widely. Since As(V) is efficiently taken up by P. vittata than As(III), As speciation by associated rhizobacteria could offer enormous possibility to enhance As phytoremediation. Specifically, increased rhizobacteria mediated As(III) to As(V) conversion appeared to be a crucial step in As mobilization and translocation. In this study, Pseudomonasvancouverensis strain m318 with the potential to improve As phytoremediation was inoculated to P. vittata in a field trial for three years to evaluate its long-term efficacy and stability for enhancing As phytoextraction. The biomass, As concentration, and As accumulation of ferns showed to be increased by inoculation treatment. Although this trend occasionally declined which may be accounted to lower As concentration in soil and amount of precipitation during experiments, the potential of inoculation was observed in increased enrichment coefficients. Further, the arsenite oxidase (aioA-like) genes in the rhizosphere were detected to evaluate the influence of inoculation on As phytoremediation. The findings of this study suggested the potential application of rhizosphere regulation to improve phytoremediation technologies for As contaminated soils. However, the conditions which set the efficacy of this method could be further optimized.

The increasing contamination of the environment with microplastic requires efficient methods for the separation and detection of these plastic particles. In this work, we present a protocol that uses Fenton oxidation to remove biological material, centrifugation to separate microplastics from soil, and Nile Red staining, fluorescence microscopy, and image processing to detect and quantify of microplastic. The main component of this work was the separation process using centrifugation. All the main polymers used in this work, polyethylene, polypropylene, polystyrene, poly (vinyl chloride), and poly (ethylene terephthalate), were efficiently recovered at more than 94 wt% from heat-altered soil using CaCl2 solution with a density of 1.4 g ml−1. The hydrophilicity of the polymer had a greater effect on the recovery than density. The protocol was then tested on agricultural soil sampled near a contaminated site. The number of microplastic particles was quantified, and the weight of microplastic in the soil was estimated. The highest contamination was observed near the hotspot at a distance of 1 m with 75✕103 particles kg−1, corresponding to a weight between 20 and 6 mg kg−1. The number of particles decreased logarithmically to 30✕103 particles kg−1 or 5 to 2 mg kg−1.

The main threats to the environment from heavy metals are associated with arsenic (As), lead (Pb) and cadmium (Cd). In this study, the potential of Pteris multifida for removing As, Pb and Cd from hydroponic solution and pot soil was evaluated for the first time. Short-term (5 day) experiments were conducted to assess phytofiltration efficiency of temperate zone fern P. multifida and to compare it with mostly studied tropical zone fern P. vittata. Within 5 days, P. multifida accumulated 33% of As(III), whereas P. vittata could not accumulate that most toxic arsenic species As(III) at all. Long-term hydroponic results showed that 90% of Pb, 50% of As and 36% of Cd were removed by P. multifida. Concentration of As in the frond (22 mg/kg dw) was comparatively higher than other parts of plant and significantly higher concentration of Cd and Pb were stored in root and rhizome. Pot soil experiment of P multifida confirmed the comparative uptake and translocation of As(V), Pb and Cd from soil. Therefore, from the assessment of heavy metal accumulation capacity, translocation and healthy survival for long time, P. multifida was identified as an excellent species for the treatment of multi-metal contaminated water and soil.

Estuaries in the areas prone to anthropogenic activities are exposed to multifarious pollutants. Toxic concentrations of heavy metals do exist with persistent organic compounds in such estuaries prolonging the recalcitrance and ecotoxicological consequences of the chemicals, which impact on the health of the brackish water and by extension, the oceans. The quest for high aesthetic quality of the estuarine environment is gaining attention from global campaign, which requires effective remedial strategies to replace the physical and chemical methods in use that are costly and often leave behind toxic residues in the environment. Contrary to physico-chemical remedial processes, bioremediation strategies are projected as a promising green technology to remove pollutants from the estuarine environment. The concept of bioremediation involves the use of competent biological elements such as microorganisms and plants, along with or without the biomolecules they produced, to ameliorate pollution. Therefore, this paper reviews the various bioremediation technologies that would be applicable to decommissioning estuarine environments polluted with toxic metals and persistent organic compounds.

Rhizodegradation of polycyclic aromatic hydrocarbons (PAHs) is a product of complex interactions between plant and bacteria. In this study, hydroponic culture of sudangrass was established in order to investigate the effects of the plant on PAHs degradation and vice versa through changes in rhizosphere bacterial community. Results showed a plant-induced variability in PAHs degradation dependent on a characteristic shift in bacterial community, with pH and plant age as driving factors. Moreover, bacterial communities with high diversity seemed to abate the phytotoxic effects of PAHs degradation as observed in the plant’s gross health. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and next-generation sequencing revealed that regardless of plant age and culture conditions, the increase or decrease of Sphingobium sp. could dictate the PAHs degradation potential of the bacterial consortium. Overall, this study utilized hydroponic culture of sudangrass to show that plant even of same species can suppress, support, or enhance PAHs degradation of bacteria depending on specific factors.

Pteris vittata and Pteris multifida are widely studied As hyperaccumulators that absorb As mainly via roots. Hence, rhizobacteria exhibit promising potential in phytoextraction owing to their immense microbial diversity and interactions with plants. Pseudomonas vancouverensis strain m318 that contains aioA-like genes was screened from P. multifida’s rhizosphere through the high As resistance (minimum inhibitory concentrations (MICs) against As(III): 16 mM; MICs against As(V): 320 mM), rapid As oxidation (98% oxidation by bacterial cultures (OD600nm = 1) from 200 μL of 0.1 mM As(III) within 24 h), predominant secretion of IAA (12.45 mg L−1) and siderophores (siderophore unit: 88%). Strain m318 showed significant chemotactic response and high colonization efficiency to P. vittata roots, which suggested its wide host affinity. Interestingly, inoculation with strain m318 enhanced the proportion of aioA-like genes in the rhizosphere. And in field trials, inoculation with strain m318 increased As accumulation in P. vittata by 48–146% and in P. multifida by 42–233%. Post-transplantation inoculations also increased As accumulation in both ferns. The abilities of the isolated multifunctional strain m318 and the increase in the rhizosphere microbial aioA-like genes are thus speculated to be involved in As transformation in the rhizospheres and roots of P. vittata and P. multifida.

As a toxic and carcinogenic metalloid, arsenic has posed serious threat to human health. Phytoremediation has emerged as a promising approach to circumvent this problem. Arsenic uptake by Pteris vittata is largely determined by arsenic speciation and mainly occurs via roots; thus, rhizospheric microbial activities may play a key role in arsenic accumulation. The aim of this study was to investigate the potential of arsenic resistant rhizobacteria to enhance arsenic phytoextraction. A total of 49 cultivable rhizobacteria were isolated from the arsenic hyperaccumulating fern, Pteris vittata, and subjected to an initial analysis to identify potentially useful traits for arsenic phytoextraction, such as arsenic resistance and the presence of aioA(aroA)-like (arsenite oxidase-like) gene. Isolated strain r507, named as Cupriavidus basilensis strain r507, was a selected candidate for its outstanding arsenic tolerance, rapid arsenite oxidation ability, and strong colonization to P. vittata. Strain r507 was used in co-cultivation trials with P. vittata in the field for six months. Results showed that the inoculation with strain r507 potentiated As accumulation of P. vittata up to 171%. Molecular analysis confirmed that the inoculation increased the abundance of aioA-like genes in the rhizosphere, which might have facilitated arsenite oxidation and absorption. The findings of this study suggested the feasibility of co-cultivating hyperaccumulators with facilitator bacteria for practical arsenic phytoremediation.

Toxic metals/metalloid contaminations of estuarine sediments due to compromised tributaries arouse significant interest in studying bacterial community that triggers natural attenuation processes. Geo-accumulation index (Igeo), contamination factor (CF), pollution load index (PLI), and Hakanson potential ecological risk index (RI) as a sum of risk factors (Er) were used to quantify toxic metal/metalloid-pollution status of Lagos Lagoon (2W) and ‘Iya-Alaro’ tributary (4W) sediments in comparison with pristine ‘Lekki Conservation Centre’ sediment (L1-B). Bacteriology of the ecosystems was based on culture-independent analyses using pyrosequencing. 2W and 4W were extremely contaminated with mercury (Igeo > 7), whereas, cadmium contamination was only observed in 4W. The two ecosystems were polluted with toxic metal based on PLI, where mercury (Er = 2900 and 1900 for 4W and 2W, respectively) posed very high ecological risks. Molecular fingerprinting revealed that Proteobacteria, Firmicutes, and Acidobacteria predominately contributed the 20 most abundant genera in the two ecosystems. The 240 and 310 species present in 2W and 4W, respectively, but absent in L1-B, thrive under the metal concentrations in the polluted hydrosphere. Whereas, the 58,000 species missing in 2W and 4W but found in L1-B would serve as indicators for systems impacted with metal eco-toxicity. Despite toxic metal pollution of the ecosystems understudied, bacterial communities play vital roles in self-recovery processes occurring in the hydrosphere.

While phytoremediation has been considered as an in situ bioprocess to remediate environmental contaminants, the application of functional endophytic bacteria within plants remains a potential strategy that could enhance the plants’ efficiency in phytoremediation. In this study, 219 endophytes were isolated from plants that are predominantly located in a constructed wetland, including reed (Phragmites australis) and water spinach (Ipomoea aquatica). Twenty-five strains of the isolated endophytes utilize aromatic compounds as sole carbon source; Achromobacter xylosoxidans strain F3B was chosen for the in planta studies using the model plant Arabidopsis thaliana. Phylogenetic analysis indicated that those endophytic isolates of A. xylosoxidans formed a cluster within its species, and a specific real-time PCR detection method was developed for confirming the stability of the isolates in plants. In the presence of either catechol or phenol, inoculation of A. thaliana with F3B could extend into the root lengths and fresh weights to promote pollutants removal rates. These results demonstrate the potential of the endophytic F3B strain for helping plants to tolerate stress from aromatic compounds and to improve phytoremediation of phenolic pollutants.