Phytoremediation of DEHP and heavy metals co-contaminated soil by rice assisted with a PGPR consortium: Insights into the regulation of ion homeostasis, improvement of photosynthesis and enrichment of beneficial bacteria in rhizosphere soil

Evaluation of electrokinetic-assisted phytoremediation efficiency of dibutyl phthalate contaminated soil by maize (Zea mays L.) under different electric field intensities

The excessive accumulation of dibutyl phthalate (DBP) in soil poses a serious threat to soil ecosystems and crop safety production. Electrokinetic-assisted phytoremediation (EKPR) has been considered as a potential technology for remediating organic contaminated soils. In order to investigate the effect of different electric fields on removal efficiency of DBP, three kinds of electric fields were set up in this study (1 V·cm-1, 2 V·cm-1 and 3 V·cm-1). The results showed that 59 % of DBP in soil was removed by maize (Zea mays L.) within 20 d in low-intensity electric field (1 V·cm-1), and the accumulation of DBP in maize tissues decreased significantly compared to the non-electrified treatment group. Interestingly, it could be observed that the low-intensity electric field could maintain ion homeostasis and improve the photosynthetic efficiency of the plant, thereby relieving the inhibition of DBP on plant growth and increasing the chlorophyll content (94.1 %) of maize. However, the removal efficiency of DBP by maize decreased significantly under the medium-intensity (2 V·cm-1) and high-intensity electric field (3 V·cm-1). Moreover, the important roles of soil enzyme and rhizosphere bacterial community in low-electric field were also investigated and discussed. This study provided a new perspective for exploring the mechanism of removing DBP through EKPR.

Drivers of the Sisrè berry plant [Synsepalum dulcificum (Schumach & Thonn.) Daniell] rhizosphere bacterial communities in Benin

Each plant species has its own rhizobacteriome, whose activities determine both soil biological quality and plant growth. Little knowledge exists of the rhizosphere bacterial communities associated with opportunity crops with high economic potential such as Synsepalum dulcificum. Native to West Africa, this shrub is famous for its red berries representing the only natural source of miraculin, a glycoprotein, with sweetening properties, but also playing a role in the treatment of cancer and diabetes. This study aimed to characterize the structure and diversity of rhizobacterial communities associated with S. dulcificum and to identify the parameters determining this diversity. An initial sampling stage allowed the collection of rhizosphere soils from 29 S. dulcificum accessions, belonging to three distinct phenotypes, from 16 municipalities of Benin, located either on farms or in home gardens. The bacterial diversity of these rhizosphere soils was assessed by Illumina sequencing of the 16S rRNA gene after DNA extraction from these soils. Furthermore, an analysis of the physicochemical properties of these soils was carried out. All accessions combined, the most represented phylum appeared to be Actinobacteriota, with an average relative abundance of 43.5 %, followed by Proteobacteria (14.8 %), Firmicutes (14.3 %) and Chloroflexi (12.2 %), yet the relative abundance of dominant phyla varied significantly among accessions (p < 0.05). Plant phenotype, habitat, climate and soil physicochemical properties affected the bacterial communities, but our study pointed out that soil physicochemical parameters were the main driver of rhizobacterial communities' structure and diversity. Among them, the assimilable phosphorus, lead, potassium, arsenic and manganese contents, texture and cation exchange capacity of rhizosphere soils were the major determinants of the composition and diversity of rhizosphere bacterial communities. These results suggested the possibility of improving the growth conditions and productivity of S. dulcificum, by harnessing its associated bacteria of interest and better managing soil physicochemical properties.

Mechanisms of biochar assisted di-2-ethylhexyl phthalate (DEHP) biodegradation in tomato rhizosphere by metabolic and metagenomic analysis

The intensive accumulation of di-2-ethylhexyl phthalate (DEHP) in agricultural soils has resulted in severe environmental pollution that endangers ecosystem and human health. Biochar is an eco-friendly material that can help in accelerating organic pollutant degradation; nevertheless, its roles in enhancing DEHP removal in rhizosphere remain unclear. This work investigated the impacts of biochar dosage (0%-2.0%) on DEHP degradation performance in tomato rhizosphere by comprehensively exploring the change in DEHP metabolites, bacterial communities and DEHP-degrading genes. Our results showed a significant increase of rhizosphere pH, organic matter and humus by biochar amendment, which achieved a satisfactorily higher DEHP removal efficiency, maximally 77.53% in treatments with 1.0% of biochar. Biochar addition also remarkably changed rhizosphere bacterial communities by enriching some potential DEHP degraders of Nocardioides, Sphingomonas, Bradyrhizobium and Rhodanobacter. The abundance of genes encoding key enzymes (hydrolase, esterase and cytochrome P450) and DEHP-degrading genes (pht3, pht4, pht5, benC-xylZ and benD-xylL) were increased after biochar amendment, leading to the change in DEHP degradation metabolism, primarily from benzoic acid pathway to protocatechuic acid pathway. Our findings evidenced that biochar amendment could accelerate DEHP degradation by altering rhizosphere soil physicochemical variables, bacterial community composition and metabolic genes, providing clues for the mechanisms of biochar-assisted DEHP degradation in organic contaminated farmland soils.

Mitigation strategies for heavy metal toxicity and its negative effects on soil and plants

Heavy metal pollution threatens food security by accumulating in crops and soils, posing a significant challenge to modern agriculture due to its high toxicity. Urgent action is needed to restore affected agricultural fields. An efficient way to remove toxins is by bioremediation, which uses microorganisms. With the purpose of restoring soil in agriculture, this research attempts to assemble a consortium of microorganisms isolated from techno-genic soil. A number of promising strains, including Pseudomonas putida, Pantoea sp., Pseudomonas aeruginosa, Klebsiella oxytoca, and Agrobacterium tumefaciens were chosen based on their capacity to eliminate heavy metals from tests. Heavy metal removal (Cd, Hg, As, Pb, and Ni) and phytohormone production have been shown to be effective using consortiums (Pseudomonas aeruginosa, Klebsiella oxytoca, and Agrobacterium tumefaciens in a 1:1:2). In instances with mixed heavy-metal contamination, aeruginosa demonstrated efficacy because of its notable ability to absorb substantial quantities of heavy metals. The capacity of the cooperation to improve phytoremediation was investigated, with an emphasis on soil cleanup in agricultural areas. When combined with Sorghum bicolor L., it was able to remove roughly 16% As, 14% Hg, 32% Ni, 26% Cd, and 33% Pb from the soil.

The uptake and degradation of polychlorinated biphenyls in constructed wetlands planted with Myriophyllum aquaticum

The unregulated dismantling and improper disposal of electronic waste lead to severe soil contamination by polychlorinated biphenyls (PCBs). Constructed wetlands (CWs) play an important role in PCBs removal as a result of the co-existence of anaerobic and aerobic conditions. However, the effects and mechanisms of different PCBs concentrations in soils on plant uptake and PCBs degradation within CWs are unclear. We evaluated the uptake and degradation of PCBs at different concentrations by Myriophyllum aquaticum (Vell.) Verdc. Planting significantly increased PCBs removal by 8.70% (p < 0.05) in soils with 1500 and 2500 μg/kg PCBs, whereas no significant effect was observed at 500 and 1000 μg/kg. PCBs levels did not significantly affect plant growth and PCBs accumulation. The contribution of plant uptake to PCBs removal was only 0.10-0.12%, indicating that microbial degradation was the dominant pathway for PCBs removal after planting with M. aquaticum. In the treatments with PCBs ≥ 1500 μg/kg, M. aquaticum increased the microbial population, altered the microbial community structure and enriched PCB-degrading bacteria. Functional prediction revealed that microbes in M. aquaticum rhizosphere secreted more peroxidase and glycosyltransferase than non-plant control, which were likely involved in PCBs metabolism.

Sphingomonas panaciterrae PB20 increases growth, photosynthetic pigments, antioxidants, and mineral nutrient contents in spinach (Spinacia oleracea L.)

Plant growth promoting rhizobacteria (PGPR) have been intensively investigated in agricultural crops for decades. Nevertheless, little information is available on the application of Sphingomonas spp. as a PGPR particularly in vegetables, despite of potential plant growth promoting traits of this group. This study investigated the role of Sphingomonas panaciterrae (PB20) on growth and nutritional profile of spinach applied through seed priming (SP), soil drenching (SD), foliar application (FA), and bacterial culture filtrate foliar (BCF) applications. The results showed that, depending on different methods of application, PB20 significantly increased plant height (19.57-65.65 %), fresh weight (7.26-37.41 %), total chlorophyll (71.14-192.54 %), carotenoid (67.10-211.67 %) antioxidant (55.99-207.04), vitamin C (8.1-94.6 %) and protein content (6.7-21.5 %) compared to control in the edible part of spinach. Among the mineral nutrients, root nitrogen (N) showed greater response to bacterial application (18.65%-46.15 % increase over control) than shoot nitrogen (6.70%-21.52 % increased over control). Likewise, in all methods of application, phosphorus (P) content showed significant increase over control both in root (42.79-78.48 %) and in shoot (3.57-27.0 %). Seed priming and foliar application of PB20 increased the shoot calcium (Ca) content compared to control. BCF foliar application yielded maximum magnesium (Mg), iron (Fe) and zinc (Zn) in shoot. However, seed priming resulted in maximum Fe in root. Overall, seed priming outperformed in growth, vitamin C, antioxidants, N and P uptake, while BCF foliar application resulted in better uptake of several nutrients. Multivariate analysis validated the positive association of most of the growth parameters with SP while several nutrients with FA and BCF. Based on the findings it is evident that this rhizobacteria PB20 has the potentiality to be applied as a biofertilizer to produce nutrient-enriched spinach with an improved yield. Farmers can conveniently incorporate PR20 through seed priming before planting of spinach, with additional benefits through foliar spray.

Combining microbiome and pseudotargeted metabolomics revealed the alleviative mechanism of Cupriavidus sp. WS2 on the cadmium toxicity in Vicia unijuga A.Br

Cadmium (Cd) pollution is one of the most severe toxic metals pollution in grassland. Vicia unijuga (V. unijuga) A.Br. planted nearby the grassland farming are facing the risk of high Cd contamination. Here, we investigated the beneficial effects of a highly Cd tolerant rhizosphere bacterium, Cupriavidus sp. WS2, on Cd contaminated V. unijuga. Through plot experiments, we set up four groups of treatments: the control group (without WS2 or Cd), the Cd group (with only Cd addition), the WS2 group (with only WS2 addition), and the WS2/Cd group (with WS2 and Cd addition), and analyzed the changes in physiological indicators, rhizosphere microorganisms, and stem and leaf metabolites of V. unijuga. Results of physiological indicators indicated that Cupriavidus sp. WS2 had strong absorption and accumulation capacity of Cd, exogenous addition of strain WS2 remarkably decreased the Cd concentrations, and increased the plant heights, the biomass, the total protein concentrations, the chlorophyll contents and the photosynthetic rate in stems and leaves of V. unijuga under Cd stress. Cd treatment increased the abundance of Cd tolerant bacterial genera in rhizosphere microbiome, but these genera were down-regulated in the WS2/Cd group. Pseudotargeted metabolomic results showed that six common differential metabolites associated with antioxidant stress were increased after co-culture with WS2. In addition, WS2 activated the antioxidant system including glutathione (GSH) and catalase (CAT), reduced the contents of oxidative stress markers including malondialdehyde (MDA) and hydrogen peroxide (H2O2) in V. unijuga under Cd stress. Taken together, this study revealed that Cupriavidus sp.WS2 alleviated the toxicity of V. unijuga under Cd exposure by activating the antioxidant system, increasing the antioxidant metabolites, and reducing the oxidative stress markers.

Pretreatment of marine sediment for the removal of di-(2-ethylhexyl) phthalate by sulfite in the presence of sorghum distillery residue-derived biochar and its effect on microbiota response

This study investigates the mechanism behind the oxidation di-(2-ethylhexyl) phthalate (DEHP) in marine sediment by coupling sulfite using biochar prepared from sorghum distillery residue (SDRBC). The rationale for this investigation stems from the need to seek effective methods for DEHP-laden marine sediment remediation. The aim is to assess the feasibility of sulfite-based advanced oxidation processes for treating hazardous materials such as DEHP containing sediment. To this end, the sediment in question was treated with 2.5 × 10-5 M of sulfite and 1.7 g L-1 of SDRBC700 at acidic pH. Additionally, the study demonstrated that the combination of SDRBC/sulfite with a bacterial system enhances DEHP removal. Thermostilla bacteria were enriched, highlighting their role in sediment treatment. This study concludes that sulfite-associated sulfate radicals-driven carbon advanced oxidation process (SR-CAOP) offers sustainable sediment pretreatment through the SDRBC/sulfite-mediated microbial consortium, in which the SO3•- and 1O2 were responsible for DEHP degradation. SDRBC/sulfite offers an effective and environmentally friendly method for removing DEHP. Further, these results can be targeted at addressing industry problems related to sediment treatment.

Metagenomic and proteomic insights into the self-adaptive cell surface hydrophobicity of Sphingomonas sp. strain PAH02 reducing the migration of cadmium-phenanthrene co-pollutant in rice

Cell surface hydrophobicity (CSH) dominates the interactions between rhizobacteria and pollutants at the soil-water interface, which is critical for understanding the dissipation of pollutants in the rhizosphere microzone of rice. Herein, we explored the effects of self-adaptive CSH of Sphingomonas sp. strain PAH02 on the translocation and biotransformation behaviour of cadmium-phenanthrene (Cd-Phe) co-pollutant in rice and rhizosphere microbiome. We evidenced that strain PAH02 reduced the adsorption of Cd-Phe co-pollutant on the rice root surface while enhancing the degradation of Phe and adsorption of Cd via its self-adaptive CSH in the hydroponic experiment. The significant upregulation of key protein expression levels such as MerR, ARHDs and enoyl-CoA hydratase/isomerase, ensures self-adaptive CSH to cope with the stress of Cd-Phe co-pollutant. Consistently, the bioaugmentation of strain PAH02 promoted the formation of core microbiota in the rhizosphere soil of rice (Oryza sativa L.), such as Bradyrhizobium and Streptomyces and induced gene enrichment of CusA and PobA that are strongly associated with pollutant transformation. Consequently, the contents of Cd and Phe in rice grains at maturity decreased by 17.2% ± 0.2% and 65.7% ± 0.3%, respectively, after the bioaugmentation of strain PAH02. These findings present new opportunities for the implementation of rhizosphere bioremediation strategies of co-contaminants in paddy fields.

Microbial interactions within beneficial consortia promote soil health

By ecologically interacting with various biotic and abiotic agents acting in soil ecosystems, highly diverse soil microorganisms establish complex and stable assemblages and survive in a community context in natural settings. Besides facilitating soil microbiome to maintain great levels of population homeostasis, such microbial interactions drive soil microbes to function as the major engine of terrestrial biogeochemical cycling. It is verified that the regulative effect of microbe-microbe interplay plays an instrumental role in microbial-mediated promotion of soil health, including bioremediation of soil pollutants and biocontrol of soil-borne phytopathogens, which is considered an environmentally friendly strategy for ensuring the healthy condition of soils. Specifically, in microbial consortia, it has been proven that microorganism-microorganism interactions are involved in enhancing the soil health-promoting effectiveness (i.e., efficacies of pollution reduction and disease inhibition) of the beneficial microbes, here defined as soil health-promoting agents. These microbial interactions can positively regulate the soil health-enhancing effect by supporting those soil health-promoting agents utilized in combination, as multi-strain soil health-promoting agents, to overcome three main obstacles: inadequate soil colonization, insufficient soil contaminant eradication and inefficient soil-borne pathogen suppression, all of which can restrict their probiotic functionality. Yet the mechanisms underlying such beneficial interaction-related adjustments and how to efficiently assemble soil health-enhancing consortia with the guidance of microbe-microbe communications remain incompletely understood. In this review, we focus on bacterial and fungal soil health-promoting agents to summarize current research progress on the utilization of multi-strain soil health-promoting agents in the control of soil pollution and soil-borne plant diseases. We discuss potential microbial interaction-relevant mechanisms deployed by the probiotic microorganisms to upgrade their functions in managing soil health. We emphasize the interplay-related factors that should be taken into account when building soil health-promoting consortia, and propose a workflow for assembling them by employing a reductionist synthetic community approach.

Fe-loaded biochar thin-layer capping for the remediation of sediment polluted with nitrate and bisphenol A: Insight into interdomain microbial interactions

The information on the collaborative removal of nitrate and trace organic contaminants in the thin-layer capping system covered with Fe-loaded biochar (FeBC) is limited. The community changes of bacteria, archaea and fungi, and their co-occurrence patterns during the remediation processes are also unknown. In this study, the optimized biochar (BC) and FeBC were selected as the capping materials in a batch experiment for the remediation of overlying water and sediment polluted with nitrate and bisphenol A (BPA). The community structure and metabolic activities of bacteria, archaea and fungi were investigated. During the incubation (28 d), the nitrate in overlying water decreased from 29.6 to 11.0 mg L-1 in the FeBC group, 2.9 and 1.8 times higher than the removal efficiencies in Control and BC group. The nitrate in the sediment declined from 5.03 to 0.75 mg kg-1 in the FeBC group, 1.3 and 1.1 times higher than those in Control and BC group. The BPA content in the overlying water in BC group and FeBC group maintained below 0.4 mg L-1 during incubation, signally lower than in the Control group. After capping with FeBC, a series of species in bacteria, archaea and fungi could collaboratively contribute to the removal of nitrate and BPA. In the FeBC group, more metabolism pathways related to nitrogen metabolism (KO00910) and Bisphenol degradation (KO00363) were generated. The co-occurrence network analysis manifested a more intense interaction within bacteria communities than archaea and fungi. Proteobacteria, Firmicutes, Actinobacteria in bacteria, and Crenarchaeota in archaea are verified keystone species in co-occurrence network construction. The information demonstrated the improved pollutant attenuation by optimizing biochar properties, improving microbial diversity and upgrading microbial metabolic activities. Our results are of significance in providing theoretical guidance on the remediation of sediments polluted with nitrate and trace organic contaminants.

The impact of main Areca Catechu root exudates on soil microbial community structure and function in coffee plantation soils

Coffee is an important cash crop worldwide, but it has been plagued by serious continuous planting obstacles. Intercropping with Areca catechu could alleviate the continuous planting obstacle of coffee due to the diverse root secretions of Areca catechu. However, the mechanism of Areca catechu root secretion in alleviating coffee continuous planting obstacle is still unclear. The changes of coffee rhizosphere soil microbial compositions and functions were explored by adding simulated root secretions of Areca catechu, the primary intercropping plant species (i.e., amino acids, plant hormone, organic acids, phenolic acids, flavonoids and sugars) in current study. The results showed that the addition of coffee root exudates altered soil physicochemical properties, with significantly increasing the availability of potassium and organic matter contents as well as promoting soil enzyme activity. However, the addition of plant hormone, organic acids, or phenolic acids led to a decrease in the Shannon index of bacterial communities in continuously planted coffee rhizosphere soil (RS-CP). The inclusion of phenolic acids specifically caused the decrease of fungal Shannon index. Plant hormone, flavonoids, phenolic acids, and sugars increased the relative abundance of beneficial bacteria with reduced bacterial pathogens. Flavonoids and organic acids increased the relative abundance of potential fungal pathogen Fusarium. The polyphenol oxidase, dehydrogenase, urease, catalase, and pH were highly linked with bacterial community structure. Moreover, catalase, pH, and soil-available potassium were the main determinants of fungal communities. In conclusion, this study highlight that the addition of plant hormone, phenolic acids, and sugars could enhance enzyme activity, and promote synergistic interactions among microorganisms by enhancing the physicochemical properties of RS-CP, maintaining the soil functions in coffee continuous planting soil, which contribute to alleviate the obstacles associated with continuous coffee cultivation.

Variance of soil bacterial community and metabolic profile in the rhizosphere vs. non-rhizosphere of native plant Rumex acetosa L. from a Sb/As co-contaminated area in China

Heavy metals (HMs) contamination poses a serious threat to soil health. However, the rhizosphere effect of native pioneer plants on the soil ecosystem remains unclear. Herein, how the rhizosphere (Rumex acetosa L.) influenced the process of HMs threatening soil micro-ecology was investigated by coupling various fractions of HMs, soil microorganisms and soil metabolism. The rhizosphere effect alleviated the HMs' stress by absorbing and reducing HMs' direct bioavailability, and the accumulation of ammonium nitrogen increased in the rhizosphere soil. Meanwhile, severe HMs contamination covered the rhizosphere effect on the richness, diversity, structure and predicted function pathways of soil bacterial community, but the relative abundance of Gemmatimonadota decreased and Verrucomicrobiota increased. The content of total HMs and physicochemical properties played a more important role than rhizosphere effect in shaping soil bacterial community. Furthermore, As was observed to have a more significant impact compared to Sb. Moreover, plant roots improved the stability of bacterial co-occurrence network, and significantly changed the critical genera. The process influenced bacterial life activity and nutrient cycling in soil, and the conclusion was further supported by the significant difference in metabolic profiles. This study illustrated that in Sb/As co-contaminated area, rhizosphere effect significantly changed soil HMs content and fraction, soil properties, and microbial community and metabolic profiles.

Endophytic Phthalate-degrading Bacillus subtilis N-1-gfp colonizing in soil-crop system shifted indigenous bacterial community to remove di-n-butyl phthalate

Endophytic bacteria can degrade toxic phthalate (PAEs). Nevertheless, the colonization and function of endophytic PAE-degrader in soil-crop system and their association mechanism with indigenous bacteria in PAE removal remain unknown. Here, endophytic PAE-degrader Bacillus subtilis N-1 was marked with green fluorescent protein gene. Inoculated strain N-1-gfp could well colonize in soil and rice plant exposed to di-n-butyl phthalate (DBP) as directly confirmed by confocal laser scanning microscopy and realtime PCR. Illumina high-throughput sequencing demonstrated that inoculated N-1-gfp shifted indigenous bacterial community in rhizosphere and endosphere of rice plants with significant increasing relative abundance of its affiliating genus Bacillus than non-inoculation. Strain N-1-gfp exhibited efficient DBP degradation with 99.7% removal in culture solutions, and significantly promoted DBP removal in soil-plant system. Strain N-1-gfp colonization help plant enrich specific functional bacteria (e.g., pollutant-degrading bacteria) with significant higher relative abundances and stimulated bacterial activities (e.g., pollutant degradation) compared with non-inoculation. Furthermore, strain N-1-gfp displayed strong interaction with indigenous bacteria for accelerating DBP degradation in soil, decreasing DBP accumulation in plants and promoting plant growth. This is the first report on well colonization of endophytic DBP-degrader Bacillus subtilis in soil-plant system and its bioaugmentation with indigenous bacteria for promoting DBP removal.

Microorganisms for Bioremediation of Soils Contaminated with Heavy Metals

Heavy-metal contaminants are one of the most relevant problems of contemporary agriculture. High toxicity and the ability to accumulate in soils and crops pose a serious threat to food security. To solve this problem, it is necessary to accelerate the pace of restoration of disturbed agricultural lands. Bioremediation is an effective treatment for agricultural soil pollution. It relies on the ability of microorganisms to remove pollutants. The purpose of this study is to create a consortium based on microorganisms isolated from technogenic sites for further development in the field of soil restoration in agriculture. In the study, promising strains that can remove heavy metals from experimental media were selected: Pantoea sp., Achromobacter denitrificans, Klebsiella oxytoca, Rhizobium radiobacter, and Pseudomonas fluorescens. On their basis, consortiums were compiled, which were investigated for the ability to remove heavy metals from nutrient media, as well as to produce phytohormones. The most effective was Consortium D, which included Achromobacter denitrificans, Klebsiella oxytoca, and Rhizobium radiobacter in a ratio of 1:1:2, respectively. The ability of this consortium to produce indole-3-acetic acid and indole-3-butyric acid was 18.03 μg/L and 2.02 μg/L, respectively; the absorption capacity for heavy metals from the experimental media was Cd (56.39 mg/L), Hg (58.03 mg/L), As (61.17 mg/L), Pb (91.13 mg/L), and Ni (98.22 mg/L). Consortium D has also been found to be effective in conditions of mixed heavy-metal contamination. Due to the fact that the further use of the consortium will be focused on the soil of agricultural land cleanup, its ability to intensify the process of phytoremediation has been studied. The combined use of Trifolium pratense L. and the developed consortium ensured the removal of about 32% Pb, 15% As, 13% Hg, 31% Ni, and 25% Cd from the soil. Further research will be aimed at developing a biological product to improve the efficiency of remediation of lands withdrawn from agricultural use.

Current Trends in Bioaugmentation Tools for Bioremediation: A Critical Review of Advances and Knowledge Gaps

Bioaugmentation is widely used in soil bioremediation, wastewater treatment, and air biofiltration. The addition of microbial biomass to contaminated areas can considerably improve their biodegradation performance. Nevertheless, analyses of large data sets on the topic available in literature do not provide a comprehensive view of the mechanisms responsible for inoculum-assisted stimulation. On the one hand, there is no universal mechanism of bioaugmentation for a broad spectrum of environmental conditions, contaminants, and technology operation concepts. On the other hand, further analyses of bioaugmentation outcomes under laboratory conditions and in the field will strengthen the theoretical basis for a better prediction of bioremediation processes under certain conditions. This review focuses on the following aspects: (i) choosing the source of microorganisms and the isolation procedure; (ii) preparation of the inoculum, e.g., cultivation of single strains or consortia, adaptation; (iii) application of immobilised cells; (iv) application schemes for soil, water bodies, bioreactors, and hydroponics; and (v) microbial succession and biodiversity. Reviews of recent scientific papers dating mostly from 2022–2023, as well as our own long-term studies, are provided here.

Combined application of allantoin and strain JIT1 synergistically or additively promotes the growth of rice under 2, 4-DCP stress by enhancing the phosphate solubility, improving soil enzyme activities and photosynthesis

Environmental pollution by 2, 4 dichlorophenol (2, 4-DCP) has become a widespread concern due to its detrimental influence on human and natural ecosystem. With the increasing accumulation of 2, 4-DCP in soil, it is of great significance to explore some appropriate approaches for enhancing plant tolerance to 2, 4-DCP stress. In the current study, a strain resistant to 2, 4-DCP was obtained from the tall fescue rhizosphere soil and named as Pseudomonas sp. JIT1. The strain JIT1 exhibited several remarkable plant growth-promoting traits, including the production of IAA, fixation of biological nitrogen and solubilization of phosphate. The inoculation of strain JIT1 significantly increased biomass, photosynthesis, antioxidant levels, chlorophyll contents and the osmotic substance contents in rice seedlings exposed to 2, 4-DCP. Meanwhile, inoculation of strain JIT1 also enhanced activities of soil alkaline phosphatase, urease, sucrase and cellulase. Moreover, under 2, 4-DCP stress, the content of allantoin in seedlings significantly increased and the pretreatment of exogenous allantoin noticeably ameliorated the negative effects caused by 2, 4-DCP stress in rice seedlings. Interesting, allantoin treatment also enhanced phosphate solubilization properties of strain JIT1. The chlorophyll contents, photosynthesis and osmotic substance further increased by combination use of strain JIT1 and allantoin, which improved the growth of seedlings, most likely to be attributed to the synergistic or additive effect between allantoin and strain JIT1. The results of this study highlight the important roles of combined use of strain JIT1 and allantoin for improving the tolerance of rice to 2, 4-DCP to stress.