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Persistent crude oil contamination poses a significant environmental challenge. In this study, the efficacy of Vigna unguiculata (L.) and associated rhizospheric microorganisms in remediating crude oil-contaminated soil within a microcosm setting was investigated. A randomized block design was employed, and soil samples were subjected to varying degrees of contamination: 0% (UR), 2.5% (CR2), 5.0% (CR5), 7.5% (CR7), and 10.0% (CR10) w/w crude oil. The investigation aimed to assess the potential of Vigna unguiculata (L.) in mitigating crude oil contamination across these defined contamination gradients. The plant growth and crude oil removal were monitored concurrently post-emergence. Plant emergence and growth were significantly affected due to contamination, especially among plants in CR5 and CR10. The bacterial population was higher in the rhizosphere, and the treatments with lower hydrocarbon contamination. It was shown that plant density encouraged the growth of bacterial communities. Significant reduction in soil TPH was observed in CR2 (76.61%) and CR7 (65.88%). There was a strong correlation between plant growth and oil-utilizing bacterial population (r2 = 0.966) and plant growth and hydrocarbon reduction (r2 = 0.956), signifying the role of plant-bacterial synergy. Saturate fractions (C30 – C32) were significantly degraded to lower molecular weight compounds (C11 – C14). Except in CR5 and CR10, the remediation within the cowpea rhizosphere was effective even at regulatory standards. Understanding the rhizosphere ecological dynamics would further highlight the role the bacteria played; hence, it is recommended. NOVELTY STATEMENT: The present study established a direct link between bacterial-plant interaction and biodegradation of crude oil. It extensively explored the nature of the degradation and also the fate of the residual oil. The present study achieved high rate of TPH removal within 12 weeks using cowpea alone as against the several previous reports that used other stimulants. [ABSTRACT FROM AUTHOR]

AbstractEvery year, a huge amount of lethal compounds, such as synthetic dyes, pesticides, pharmaceuticals, hydrocarbons, etc. are mass produced worldwide, which negatively affect soil, air, and water quality. At present, pesticides are used very frequently to meet the requirements of modernized agriculture. The Food and Agriculture Organization of the United Nations (FAO) estimates that food production will increase by 80% by 2050 to keep up with the growing population, consequently pesticides will continue to play a role in agriculture. However, improper handling of these highly persistent chemicals leads to pollution of the environment and accumulation in food chain. These effects necessitate the development of technologies to eliminate or degrade these pollutants. Degradation of these compounds by physical and chemical processes is expensive and usually results in secondary compounds with higher toxicity. The biological strategies proposed for the degradation of these compounds are both cost-effective and eco-friendly. Microbes play an imperative role in the degradation of xenobiotic compounds that have toxic effects on the environment. This review on the fate of xenobiotic compounds in the environment presents cutting-edge insights and novel contributions in different fields. Microbial community dynamics in water bodies, genetic modification for enhanced pesticide degradation and the use of fungi for pharmaceutical removal, white-rot fungi’s versatile ligninolytic enzymes and biodegradation potential are highlighted. Here we emphasize the factors influencing bioremediation, such as microbial interactions and carbon catabolism repression, along with a nuanced view of challenges and limitations. Overall, this review provides a comprehensive perspective on the bioremediation strategies. [ABSTRACT FROM AUTHOR]

The agricultural ecosystem is moderately contaminated with mercury due to industries, mining, and farming activities. Mercury concentrations in agrarian lands depend on pH, organic matter, soil texture, vegetation cover, and land usage. The legume-rhizobia symbiosis is an effective rhizoremediation tool to lessen mercury and recover soil nitrogen. Mercury-resistant rhizobia in the roots of legumes assist the host by alleviating the phytotoxicity of Hg by stabilizing Hg in the roots and producing plant growth-promoting substances. The mechanisms of Hg resistance in rhizobia include reducing mercury to a volatile form (Hg0) and sequestering in the cell wall. Legume roots can phytostabilize mercury due to their high biomass. Thus, the translocation of mercury to shoot is low, with less than one translocation and bioaccumulation factor. Sulfur compounds, enzymes, amino polycarboxylic acids, and low molecular weight organic acids can enhance mercury phytoremediation by improving plant biomass and mercury uptake. Mercury stress increases free radical scavenging in nodules. Therefore, legumes and the associated rhizobia are sustainable tools for the remediation of polluted soil. However, Hg toxicity affects nodulation by rhizobia, nodule number, morphology, weight, and micro-community structure. Contemplating the harmfulness of mercury on rhizobia, effective rhizoremediation strategies can be developed to reduce mercury in agroecosystems. [ABSTRACT FROM AUTHOR]

The utilization of plant growth promoting rhizobacteria (PGPR) is a potential strategy to ameliorate the rhizoremediation effect in the heavy metals (HMs) contaminated soil. In this study, a new heavy metal tolerant PGPR, Sphingomonas sp. PbM2, was isolated from the rhizosphere of maize. The siderophore production and 1-aminocyclopropane-1-carboxylic acid deaminase activity of PbM2 were superior to that of Novosphingobium sp. CuT1, an HM-tolerant PGPR, while the indole-3-acetic acid productivity of PbM2 was inferior to that of CuT1. The inoculation effect of the PGPR (PbM2 alone or a mixture of PbM2 and CuT1) on the rhizoremediation performance of HM-contaminated soil planted with maize was compared. Cu bioavailability was enhanced with PGPR treatment, while the bioconcentration factor significantly increased or remained steady depending on the HM concentration (200, 500, or 1000 mg/kg-soil) and remediation period (20 or 60 d). PGPR inoculation significantly enhanced soil PGP activity except for siderophores but was not statistically associated with improved plant growth. The dynamics change in the bacterial communities during rhizoremediation was similar for all soil conditions regardless of PGPR inoculation. Network analysis revealed that both the inoculated PGPR and indigenous rhizobacteria contributed to Cu bioavailability and soil PGP activity. These results suggest that the inoculation of PGPR is effective in the remediation performance of contaminated soil in which autogenous PGPR is inhibited. [ABSTRACT FROM AUTHOR]

Here, a pot experiment was designed to evaluate the phytoremediation potential of ryegrass (Lolium perennne L.) for Pb- and Cd-polluted soils under various drought levels in the presence of farmyard manure (FYM). Three levels of Pb (0, 300, and 600 mg kg−1), Cd (0, 100, and 200 mg kg−1), and drought (field capacity 100, 50, and 30%) as well as two levels of FYM (0 and 1%) were used in this experiment. Results from this study showed a significant decrease (up to 84%) in the overall growth and physiology of ryegrass. A substantial increase in antioxidants (SOD, CAT, and POD) was observed under HMs and drought stress. By the application of FYM, antioxidant activities were significantly reduced. The ryegrass accumulated higher amounts of Pb (up to 150 mg kg−1 in shoots and 193 mg kg−1 in roots) and Cd (up to 71 mg kg−1 in shoots and 92 mg kg−1 in roots) in plant tissues; however, an FYM addition significantly reduced the accumulation of both metals. Furthermore, the results of this research indicated that ryegrass has a promising ability to phytoremediate Pb and Cd, and the addition of FYM may be helpful in enhancing metal stabilization and plant growth despite water constraints. [ABSTRACT FROM AUTHOR]

Hydrocarbonoclastic bacterial strains were isolated from rhizosphere of plants growing in crude oil-contaminated sites of Assam, India. These bacteria showed plant growth-promoting attributes, even when exposed to crude oil. Two independent pot trials were conducted to test the rhizodegradation ability of the bacterial consortium in combination of plants Azadirchta indica or Delonix regia in crude oil-contaminated soil. Field experiments were conducted at two crude oil-contaminated agricultural field at Assam (India), where plants (A. indica or D. regia) were grown with the selected bacterial consortium consisting of five hydrocarbonoclastic bacterial isolates (Gordonia amicalis BB-DAC, Pseudomonas aeruginosa BB-BE3, P. citronellolis BB-NA1, Rhodococcus ruber BB-VND, and Ochrobactrum anthropi BB-NM2), and NPK was added to the soil for biostimulation. The bacterial consortium-NPK biostimulation led to change in rhizosphere microbiome with enhanced degradation of petroleum hydrocarbons (PHs) in soils contaminated with crude oil. After 120 days of planting A. indica + consortium + NPK treatment, degradation of PHs was found to be up to 67%, which was 55% with D. regia with the same treatment. Significant changes in the activities of plant and soil enzymes were also noted. The shift is bacterial community was also apparent as with A. indica, the relative abundance of Proteobacteria, Actinobacteria, and Acidobacteria increased by 35.35%, 26.59%, and 20.98%, respectively. In the case of D. regia, the relative abundance of Proteobacteria, Actinobacteria, and Acidobacteria were increased by 39.28%, 35.79%, and 9.60%, respectively. The predicted gene functions shifted in favor of the breakdown of xenobiotic compounds. This study suggests that a combination of plant-bacterial consortium and NPK biostimulation could be a productive approach to bioengineering the rhizosphere microbiome for the purpose of commercial bioremediation of crude oil-contaminated sites, which is a major environmental issue faced globally. [ABSTRACT FROM AUTHOR]

Contamination of soil through hexavalent chromium Cr (VI) has increased rapidly during the last few decades. Cr (VI) is a bio-accumulative hazardous metal that can lead to harmful health effects on human being. Several treatment technologies have been used for the treatment of Cr, however, most of them are having some serious limitations. Biological Cr-removal can replace existing physicochemical approaches. The usefulness of phytoremediation in contaminated settings is limited by the sluggish growth rate of plants and low metal absorption. This situation could be mitigated and phytoremediation efficiency can be accelerated by introducing chromium-resistant plant growth-promoting bacterium (PGPB). PGPB inoculation may promote plant growth by producing growth-promoting chemicals and heavy metal remediation by secreting chelating agents, acidification, and redox alterations. Bacterial inoculation improved metal tolerance and absorption through modulating metal transporter, tolerant, and chelator genes. To decrease the harmful impacts brought about by high metal concentrations, PGPB application has shown great potential. The precise molecular mechanism of PGPR-mediated phytoremediation of heavy metals and the stimulation of plant development, however, is little understood. In addition to illuminating the mechanisms underlying plant metal accumulation, this review includes information on the characteristics and mechanisms that PGPB possesses to enhance plant metal tolerance and growth. We evaluated several recent studies of chromium phytoremediation, augmenting the phytoremediation of chromium through PGPB. Examining the possible contribution of bacteria that promote plant growth in microbe-assisted phytoremediation is the goal of this review. The molecular processes by which PGPB strains promote plant development and clean the soil contaminated with chromium are well described in the present review. [ABSTRACT FROM AUTHOR]

Rhizoremediation involves the use of plants and plant growth promoting rhizobacteria (PGPR) for remediation of contaminated soil. This study evaluated the use of Pseudomonas aeruginosa and Eleusine indica to remediate cadmium-polluted soil. Soil samples were collected around the roots of E. indica and PGPR were isolated and evaluated for their capacity for plant growth promotion. P. aeruginosa was selected for Cd remediation experiment which was based on treatments T1 (control soil), T2 (soil + cadmium), T3 (soil + plant + Cd + Pseudomonas applied 2x monthly) T4 (Soil + Plant + Cd + Pseudomonas applied once). T5 (soil + plant + Cd + Pseudomonas applied 1x monthly) T6 (soil + plant + Cd) and T7 (soil and plant). Cd concentration in soil treatments was equivalent to 8 mg/kg and treatments were monitored for 2 months. Bacterial count, physicochemical parameters, nutrient analyses, and Cd removal were subsequently evaluated. T3 had higher bacterial count and pH values (p < 0.05) relative to other treatments and this could be due to the inoculum addition. Conversely, reduction in electrical conductivity, organic carbon and organic matter observed in T3 could be attributed to improved rhizospheric activities. Again, rhizoremediation was highest (P < 0.05) in T3 (90 %) and this suggests P aeruginosa made bio-absorption of Cd easier for E. indica relative to treatments that do not have the inoculum. This study showed that E. indica together with P. aeruginosa are suitable candidates for phytoremediation of Cd contaminated soils. [ABSTRACT FROM AUTHOR]

Rhizoremediation involves the use of plants and plant growth promoting rhizobacteria (PGPR) for remediation of contaminated soil. This study evaluated the use of Pseudomonas aeruginosa and Eleusine indica to remediate cadmium-polluted soil. Soil samples were collected around the roots of E. indica and PGPR were isolated and evaluated for their capacity for plant growth promotion. P. aeruginosa was selected for Cd remediation experiment which was based on treatments T1 (control soil), T2 (soil + cadmium), T3 (soil + plant + Cd + Pseudomonas applied 2x monthly) T4 (Soil + Plant + Cd + Pseudomonas applied once). T5 (soil + plant + Cd + Pseudomonas applied 1x monthly) T6 (soil + plant + Cd) and T7 (soil and plant). Cd concentration in soil treatments was equivalent to 8 mg/kg and treatments were monitored for 2 months. Bacterial count, physicochemical parameters, nutrient analyses, and Cd removal were subsequently evaluated. T3 had higher bacterial count and pH values (p < 0.05) relative to other treatments and this could be due to the inoculum addition. Conversely, reduction in electrical conductivity, organic carbon and organic matter observed in T3 could be attributed to improved rhizospheric activities. Again, rhizoremediation was highest (P < 0.05) in T3 (90 %) and this suggests P aeruginosa made bio-absorption of Cd easier for E. indica relative to treatments that do not have the inoculum. This study showed that E. indica together with P. aeruginosa are suitable candidates for phytoremediation of Cd contaminated soils.

Polycyclic aromatic hydrocarbons (PAHs) are composed of a number of aromatic rings. They are produced because of the incomplete burning of many organic materials like gasoline, charcoal, burning biomass during forest fires, or oil. Consumption of products from sources contaminated by PAHs may be harmful to humans and other animals, as many of these compounds have been involved in causing tumors in animals and cancer in humans. Thus, degradation of these hazardous contaminants is of utmost importance to maintain a clean and healthy environment. While various physicochemical methods have been employed to eliminate these compounds from our surroundings, there are several limitations, like being costly and producing harmful end products. Micro-organisms have an enormous potential for bioremediation, given that they are capable of processing and degrading PAHs. Also, they provide an eco-friendly method of remediation. This review primarily focuses on different PAHs and relevant bioremediation techniques for PAH degradation, either directly or indirectly (rhizoremediation). Further, several genes encoding PAH-catabolic enzymes accountable for effective PAH degradation have also been discussed, along with strategies for utilization of bioremediation at the field level. [ABSTRACT FROM AUTHOR]

Rhizoremediation is a promising method based on the synergism between plant and rhizobacteria to remediate soil co-contaminated with heavy metals and total petroleum hydrocarbons (TPHs). A plant growth–promoting (PGP) rhizobacterium with diesel-degrading capacity and heavy metal tolerance was isolated from the rhizosphere of tall fescue (Festuca arundinacea L.), after which the effects of its inoculation on rhizoremediation performance were evaluated in heavy metal– and diesel-contaminated soil planted with tall fescue. The bacterial isolate (Novosphingobium sp. CuT1) was characterized by its indole-3-acetic acid (IAA) production, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, and siderophore productivity as PGP traits. CuT1 was able to grow on 1/10 LB-agar plates containing 5 mM of Cu or 5 mM of Pb. To evaluate the remediation effect of heavy metal– and diesel-contaminated soil by CuT1 inoculation, the experimental conditions were prepared as follows. The soil was artificially contaminated with heavy metals (Cu and Pb) at a final concentration of 500 ppm. The soil was then further contaminated with diesel at final concentrations of 0, 10,000, and 30,000 ppm. Finally, all plots were planted with tall fescue, a representative hyperaccumulating plant. Compared to the rhizoremediation performance of the co-contaminated soil (Cu + Pb + diesel) without inoculation, the bioavailable Cu concentrations in the soil and the tall fescue biomass were significantly increased in CuT1 inoculation. Additionally, the root growth of tall fescue was also promoted in CuT1 inoculation. Correlation analysis showed that Cu bioavailability and bioconcentration factor were positively correlated with CuT1 inoculation. The diesel removal efficiency showed a positive correlation with CuT1 inoculation, although the diesel removal was below 30%. CuT1 inoculation was positively correlated with IAA and dehydrogenase activity in the soil. Moreover, the dry biomass of the tall fescue's roots was highly associated with CuT1 inoculation. Collectively, our findings suggest that Novosphingobium sp. CuT1 can be utilized as an applicable bioresource to enhance rhizoremediation performance in heavy metal– and TPH-contaminated soils. [ABSTRACT FROM AUTHOR]

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Aim: Tomato‐associated plant‐growth‐promoting rhizosphere bacteria were screened for effective antagonistic activity against the fungal vascular wilt pathogens; tolerance to heavy metals; and enhancing the bioavailability of iron for tomato plants through in vitro and in vivo approaches. Methods and Results: Among the 121 rhizobacteria screened for siderophores, 25 isolates were observed to be siderophore producers and out of these, seven isolates chelate copper and iron thus exhibiting in vitro antagonism against the virulent strains of Fusarium oxysporum f. sp. lycopersici MTCC10270 (Fol), Fusarium equiseti MFol and Sarocladium sp. SWL isolated from infected tomatoes. Pseudomonas stutzeri KRP8 was identified to be the most potent strain among the siderophore producers and its siderophores were chemically characterized by mass spectra as metal bound and metal‐free forms. Upon bio‐inoculation of fortified bacterial consortium (siderozote) into the rhizosphere of vermiculite pot cultured tomatoes supplied with varying concentrations of iron and copper ions, we observed in planta growth improvements, antagonism, enhancement of bioavailability of iron and heavy metal tolerance using Inductively Coupled Plasma‐Optical Emission Spectrometry. Conclusion and Significance of the Study: Our rhizobacterial consortium provides an opportunity for soil reclamation through an ecofriendly method for a heavy metal‐free agricultural landscape. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are introduced to the environment from anthropogenic and natural sources. The most significant natural source of PAH are wildfires and volcanic eruptions. The PAHs occurring in the soil mostly bind to the root system of plants. Phytodegradation, specifically rhizospheric degradation, can reduce the PAH levels in soil with the help of plants roots. A pot experiment was conducted to study the effect of application of soil amendments on the PAHs level in the burnt soil (BS). The aim of this study was to assess the effect of application of soil amendments (compost, biochar, and bentonite) on the PAHs level after performing experiment with two grass species (Lolium perenne, Festuca rubra). Biochar and compost turned out to be the most effective amendments, regardless of the used grass species. Phytomanaged BS without added amendments also demonstrated the potential for PAH dissipation, but only in the case of Festuca rubra. It has been proven that the application of soil amendments together with the test grass species induced important changes in the BS properties (alteration of soil pH with related change of Kow of individual PAHs; root system on which soil microorganisms thrive) which evoked an increased bioavailability of PAHs.

Rhizoremediation and bioaugmentation have proven effective in promoting benzo[a]pyrene (BaP) degradation in contaminated soils. However, the mechanism underlying bioaugmented rhizospheric BaP degradation with native microbes is poorly understood. In this study, an indigenous BaP degrader (Stenotrophomonas BaP-1) isolated from petroleum-contaminated soil was introduced into ryegrass rhizosphere to investigate the relationship between indigenous degraders and rhizospheric BaP degradation. Stable isotope probing and 16S rRNA gene amplicon sequencing subsequently revealed 15 BaP degraders, 8 of which were directly associated with BaP degradation including Bradyrhizobium and Streptomyces. Bioaugmentation with strain BaP-1 significantly enhanced rhizospheric BaP degradation and shaped the microbial community structure. A correlation of BaP degraders, BaP degradation efficiency, and functional genes identified active degraders and genes encoding polycyclic aromatic hydrocarbon-ring hydroxylating dioxygenase (PAH-RHD) genes as the primary drivers of rhizospheric BaP degradation. Furthermore, strain BaP-1 was shown to not only engage in BaP metabolism but also to increase the abundance of other BaP degraders and PAH-RHD genes, resulting in enhanced rhizospheric BaP degradation. Metagenomic and correlation analyses indicated a significant positive relationship between glyoxylate and dicarboxylate metabolism and BaP degradation, suggesting a role for these pathways in rhizospheric BaP biodegradation. By identifying BaP degraders and characterizing their metabolic characteristics within intricate microbial communities, our study offers valuable insights into the mechanisms of bioaugmented rhizoremediation with indigenous bacteria for high-molecular-weight PAHs in petroleum-contaminated soils. [Display omitted] • Introduced strain boosts benzo[a]pyrene (BaP) degraders & functional gene abundance. • Introduced strain enhances rhizospheric BaP degradation, shapes microbial community. • First stable isotope probing-metagenomics for BaP bioaugmentation in rhizosphere. • Glyoxylate and dicarboxylate drive rhizospheric BaP biodegradation. • Novel identification of degraders linked to BaP degradation. [ABSTRACT FROM AUTHOR]

Environmental contamination with heavy metals is one of the major problems caused by human activity. The plant–microorganism interaction is one approach for the remediation of heavy metals contaminated soils. The current research was conducted to study the effect of Bacillus subtilis on the phytoremediation potential of Ocimum basilicum L. in lead-contaminated soil. A pot experiment was conducted to investigate the influence of Bacillus subtilis addition on the phytoremediation potential of Ocimum basilicum in lead-contaminated soil. Quantities of Pb from soil and plant samples (roots, stems and leaves) were analyzed by atomic absorption spectrophotometer using a SHIMADZU AA-7000 spectrometer. Heavy metal translocation ability of Ocimum basilicum plants from roots to the shoot was evaluated using the translocation factor while metal translocation from soil to shoot was determined by the bioaccumulation factor. The Pb concentration was reported as mg/kg dry weight. The results obtained from this study showed that Bacillus subtilis inoculated plants accumulated lead in higher concentrations compared to the treatment without the addition of microorganisms. Lead concentrations in different tissues occurred in the following order: root > stem > leaf. Inoculation of B. subtilis improved the phytoextraction efficiency of Ocimum basilicum in lead-contaminated soil. This study suggested that the application of microorganisms could greatly enhance the rhizoremediation of plants for heavy metals. [ABSTRACT FROM AUTHOR]

Crude oil/petroleum hydrocarbons (PHs) are major pollutants worldwide. In the present study, three bacterial isolates -Pseudomonas aeruginosa BB-BE3, P. aeruginosa BBBJ, and Gordonia amicalis BB-DAC were selected for their efficient hydrocarbon degradation and plant growth promotion (PGP) abilities. All three isolates were positive for siderophore production, phosphate solubilization, and IAA production, even in the presence of crude oil. The rhizoremediation ability was validated through pot trials where all three isolates promoted the growth of the Azadirachta indica plant in crude oil-contaminated soils. Treatment with the combination of the plant (A. indica) and bacteria, i.e., Pseudomonas aeruginosa BB-BE3; P. aeruginosa BBBJ; Gordonia amicalis BB-DAC showed 95.71, 93.28, and 89.88% removal of TPHs respectively, while the treatment with the plant (only) resulted in 13.44% removal of TPHs whereas, in the control (Sterile bulk soil + Crude oil), the hydrocarbon removal percentage was only 5.87%. The plant tissues were analyzed for catalase (CAT) and peroxidase (POX) activities, and the plants augmented with bacterial strains had significantly low CAT and POX activities as compared to uninoculated control. Therefore, the results suggest that the A. indica plant, in symbiotic association with these hydrocarbonoclastic rhizobacteria, could be used for bioremediation of crude oil-polluted soil. The main objective of the present study is to evaluate the potential of plant–microbe associations, also including Gordonia amicalis with the Azadirachta indica, for the rhizoremediation of petroleum hydrocarbon (PHs) polluted soil. For rhizoremediation strategy, a stable plant-bacteria partnership is important, along with effective remediation, and the Gordonia amicalis–Azadirachta indica pair is being described here for the first time, for this purpose. This plant-microbe pair was highly effective as also validated through pot trials. The hydrocarbonoclastic rhizobacteria (G. amicalis BB-DAC), in symbiotic association with the A. indica plant, has significantly degraded TPHs. [ABSTRACT FROM AUTHOR]

Cadmium is a highly toxic environmental pollutant that is known to show lethal effects on the macro- and microorganisms. The current study is aimed at the isolation and screening of cadmium-resistant bacteria from contaminated soil samples collected from the rhizosphere region wet land paddy fields near Katpadi, Vellore. Cadmium concentration in the rhizosphere soil samples was estimated by atomic absorption spectroscopy (AAS) and was found to be 2.59 mg/kg. A total of four morphologically distinct bacterial colonies were isolated and named VITATJM1, VITATJM2, VITATJM3 and VITATJM4. Maximum tolerable concentration (MTC) studies were also performed to establish the maximum concentration of Cd at which the bacteria can survive. The cultures were able to tolerate a maximum cadmium concentration of up to 500 ppm. PGPR tests such as ammonia production, phosphate solubilization, hydrogen cyanide (HCN) production and indole-3-acetic acid (IAA) were performed, and cultures VITATJM1 and VITATJM4 were found to be strongly effective. Similarly, isolates were also capable of forming biofilms. Pot culture studies were performed using Pennisetum purpureum plants, with different concentrations of cadmium in combination with bacterial culture (VITATJM1 and VITATJM4) for 30 days. From the current study, it can be concluded that application of P. purpureum augmented with bacteria in the rhizosphere could be an effective strategy for the removal of cadmium. [ABSTRACT FROM AUTHOR]

The use of plant growth-promoting rhizobacteria (PGPR) as a bioremediation enhancer in plant-assisted phytoremediation requires several steps, consisting of the screening, selection, and characterization of isolates. A subset of 50 bacterial isolates representing a wide phylogenetic range were selected from 438 morphologically different bacteria that were originally isolated from a petroleum hydrocarbon (PHC)-polluted site of a former petrochemical plant. Selected candidate bacteria were screened using six conventional plant growth-promoting (PGP) traits, complemented with the genetic characterization of genes involved in alkane degradation, as well as other pertinent functions. Finally, the bacterial isolates were subjected to plant growth promotion tests using a gnotobiotic approach under normal and stressed conditions. Our results indicated that 35 bacterial isolates (70%) possessed at least four PGP traits. Twenty-nine isolates (58%) were able to utilize n -hexadecane as a sole carbon source, whereas 43 isolates (86%) were able to utilize diesel as the sole carbon source. The presence of catabolic genes related to hydrocarbon degradation was assessed using endpoint PCR, with the alkane monooxygenase (alkB) gene found in 34 isolates, the cytochrome P450 hydroxylase (CYP153) gene found in 24 isolates, and the naphthalene dioxygenase (nah1) gene found to be present in 33 isolates. Thirty-six strains (72%) promoted canola root elongation in the growth pouch assay. After several rounds of screening, seven bacterial candidates (individually or combined in a consortium) were tested for canola root and shoot growth promotion in substrates amended by different concentrations of n -hexadecane (0%, 1%, 2%, and 3%) under gnotobiotic conditions. Our results showed that Nocardia sp. (WB46), Pseudomonas plecoglossicida (ET27), Stenotrophomonas pavanii (EB31), and Gordonia amicalis (WT12) significantly increased the root length of canola grown in 3% n -hexadecane compared with the control treatment, whereas Nocardia sp. (WB46) and Bacillus megaterium (WT10) significantly increased shoot length compared to control treatment at the same concentration of n -hexadecane. The consortium had a significant enhancement effect on root length compared to all isolates inoculated individually or to the control. This study demonstrates that the combination of PGPR traits and the PHC degradation potential of bacteria can result in an enhanced beneficial effect in phytoremediation management, which could lead to the development of innovative bacterial inoculants for plants to remediate PHC-contaminated soils. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are introduced to the environment from anthropogenic and natural sources. The most significant natural source of PAH are wildfires and volcanic eruptions. The PAHs occurring in the soil mostly bind to the root system of plants. Phytodegradation, specifically rhizospheric degradation, can reduce the PAH levels in soil with the help of plants roots. A pot experiment was conducted to study the effect of application of soil amendments on the PAHs level in the burnt soil (BS). The aim of this study was to assess the effect of application of soil amendments (compost, biochar, and bentonite) on the PAHs level after performing experiment with two grass species (Lolium perenne, Festuca rubra). Biochar and compost turned out to be the most effective amendments, regardless of the used grass species. Phytomanaged BS without added amendments also demonstrated the potential for PAH dissipation, but only in the case of Festuca rubra. It has been proven that the application of soil amendments together with the test grass species induced important changes in the BS properties (alteration of soil pH with related change of Kow of individual PAHs; root system on which soil microorganisms thrive) which evoked an increased bioavailability of PAHs. [ABSTRACT FROM AUTHOR]

The use of plant growth-promoting rhizobacteria (PGPR) as a bioremediation enhancer in plant-assisted phytoremediation requires several steps, consisting of the screening, selection, and characterization of isolates. A subset of 50 bacterial isolates representing a wide phylogenetic range were selected from 438 morphologically different bacteria that were originally isolated from a petroleum hydrocarbon (PHC)-polluted site of a former petrochemical plant. Selected candidate bacteria were screened using six conventional plant growth-promoting (PGP) traits, complemented with the genetic characterization of genes involved in alkane degradation, as well as other pertinent functions. Finally, the bacterial isolates were subjected to plant growth promotion tests using a gnotobiotic approach under normal and stressed conditions. Our results indicated that 35 bacterial isolates (70%) possessed at least four PGP traits. Twenty-nine isolates (58%) were able to utilize n-hexadecane as a sole carbon source, whereas 43 isolates (86%) were able to utilize diesel as the sole carbon source. The presence of catabolic genes related to hydrocarbon degradation was assessed using endpoint PCR, with the alkane monooxygenase (alkB) gene found in 34 isolates, the cytochrome P450 hydroxylase (CYP153) gene found in 24 isolates, and the naphthalene dioxygenase (nah1) gene found to be present in 33 isolates. Thirty-six strains (72%) promoted canola root elongation in the growth pouch assay. After several rounds of screening, seven bacterial candidates (individually or combined in a consortium) were tested for canola root and shoot growth promotion in substrates amended by different concentrations of n-hexadecane (0%, 1%, 2%, and 3%) under gnotobiotic conditions. Our results showed that Nocardia sp. (WB46), Pseudomonas plecoglossicida (ET27), Stenotrophomonas pavanii (EB31), and Gordonia amicalis (WT12) significantly increased the root length of canola grown in 3% n-hexadecane compared with the control treatment, whereas Nocardia sp. (WB46) and Bacillus megaterium (WT10) significantly increased shoot length compared to control treatment at the same concentration of n-hexadecane. The consortium had a significant enhancement effect on root length compared to all isolates inoculated individually or to the control. This study demonstrates that the combination of PGPR traits and the PHC degradation potential of bacteria can result in an enhanced beneficial effect in phytoremediation management, which could lead to the development of innovative bacterial inoculants for plants to remediate PHC-contaminated soils.

During rhizoremediation process, plant roots secrete the specific exudates which enhance or stimulate growth and activity of microbial community in the rhizosphere resulting in effective degradation of pollutants. The present study characterized cowpea (CP) and mung bean (MB) root exudates and examined their influences on the degradation of total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs) by the two oil degraders Micrococcus luteus WN01 and Bacillus cereus W2301. The effects of root exudates on soil microbial population dynamic and their enzymes dehydrogenase (DHA), and catechol 2,3 dioxygenase (C23O) activities were assessed. Both root exudates enhanced the degradation by both oil degraders. Cowpea root exudates maximized the removal of TPHs and PAHs by M. luteus WN01. Both bacterial population and DHA increased significantly in the presence of both root exudates. However, the C23O activities were significantly higher in WN01 treated. No significant influence of root exudates was observed on the C23O activities of W2301 treated. By using gas chromatography -mass spectroscopy, the dominant compounds found in cowpea and mung bean root exudates were 4-methoxy-cinnamic acid and terephthalic acid. Found in lower amount were propionic, malonic acid, and citric acid which were associated with enhanced PAHs desorption from soil and subsequent degradation. Novelty statement This is the first study to characterize the low molecular weight organic acids from root exudates of cowpea and mung bean and their influences on hydrocarbon desorption and hence enhancing the biodegradation process. The findings of the present study will greatly contribute to a better understanding of plant-microbe interaction in total petroleum hydrocarbons contaminated soil. [ABSTRACT FROM AUTHOR]

The potentials of Luffa aegyptiaca and its rhizospheric, non-mycorrhizal fungi in biodegrading and bio-remediating hydrocarbon contaminated soil were investigated in-vitro and in-situ. Biodegradation study was done in two stages: preliminary study using hydrocarbon treated filter paper and in-vitro with Mineral Salt Media (MSM) read on Spectrophotometer at two photo synthetically active wavelengths (530 nm and 620 nm) while rhizoremediation study was done in-situ in contaminated plot of land. Hydrocarbon utilization ability of the fungi and plant were confirmed using total petroleum hydrocarbon (TPH) analysis and gas chromatography mass spectroscopy (GC-MS). Results show differing rates of hydrocarbon utilization by isolated fungi. In-vitro biodegradation study showed that Aspergillus niger, Fusarium solani, Curvularia lunata and Trichoderma harzianum were best in degrading kerosene (78%), diesel (70%), spent engine oil (83%) and crude oil (77%) respectively. Rhizoremediation study using L. aegyptiaca and C. lunata show that remediation was enhanced to 72.15% as against 32.32% and 14% when only the plant or fungus is used respectively. Hydrocarbon accumulation by L. aegyptiaca also decreased in the presence of the fungus. Curvularia lunata is shown in this study to enhance the germination, survival, growth and bioremediation efficiency of L. aegyptiaca in polluted environment. Novelty statement The potentials of Curvularia lunata, a non-mycorrhizal fungi associated with L. aegyptiaca in survival, growth and phytoremediation of petroleum hydrocarbon polluted soil by L. aegyptiaca is highlighted in this study. Luffa aegyptiaca and its associated fungi is shown to bio-remediate petroleum hydrocarbon through phyto-accumulation and rhizosphere effect. [ABSTRACT FROM AUTHOR]

The objective of this study was to characterize the effects of organic soil amendment (compost) on bacterial populations associated with petroleum hydrocarbon (PH) degradation and nitrous oxide (N2O) dynamics via pot experiments. Soil was artificially contaminated with diesel oil at total petroleum hydrocarbon (TPH) concentration of 30,000 mg·kg-soil−1 and compost was mixed with the contaminated soil at a 1:9 ratio (w/w). Maize seedlings were planted in each pot and a total of ten pots with two treatments (compost-amended and unamended) were prepared. The pot experiment was conducted for 85 days. The compost-amended soil had a significantly higher TPH removal efficiency (51.1%) than unamended soil (21.4%). Additionally, the relative abundance of the alkB gene, which is associated with PH degradation, was higher in the compost-amended soil than in the unamended soil. Similarly, cnorB and nosZ (which are associated with nitric oxide (NO) and N2O reduction, respectively) were also highly upregulated in the compost-amended soil. Moreover, the compost-amended soil exhibited higher richness and evenness indices, indicating that bacterial diversity was higher in the amended soil than in the unamended soil. Therefore, our findings may contribute to the development of strategies to enhance remediation efficiency and greenhouse gas mitigation during the rhizoremediation of diesel-contaminated soils. [ABSTRACT FROM AUTHOR]

Abstract Trees occurring on the margins of agricultural areas can mitigate damage from residual herbicides. Rhizospheric microbial activity associated with trees is one of the main remedial capacity indicators. The objective of this study was to evaluate the rhizospheric microbiological activity in tree species subjected to the herbicides atrazine and sulfentrazone via the rhizosphere. The experiment was designed in four blocks and a 6 × 3 factorial scheme. The first factor consisted of six tree species from Brazil and the second of atrazine, sulfentrazone, and water solutions. Four herbicide applications were performed via irrigation. The total dry mass of the plants, mycorrhizal colonization, number of spores, basal respiration of the rhizospheric soil, and survival rate of bioindicator plants after phytoremediation were determined. Trichilia hirta had higher biomass when treated with atrazine and sulfentrazone. Herbicides decreased the microbial activity in Triplaris americana and did not affect the microbiological indicators of Myrsine gardneriana, Schizolobium parahyba, and Toona ciliata. Fewer bioindicator plants survived in soil with Triplaris americana and sulfentrazone. Microbiological indicators were influenced in different ways between species by the presence of herbicides in the rhizosphere.

This study aimed to evaluate the potential of a salt marsh plant and its rhizosphere microorganisms for the removal of two pharmaceutical compounds, bezafibrate and paroxetine, from estuarine environment. Plants were exposed for 7 days to a simplified estuarine medium, elutriate solution with or without sediment, doped with bezafibrate or paroxetine. Tests were done in absence and presence of nutrients or copper. Phragmites australis (Cav.) Trin. Ex Steud, alone or with the sediment microbial communities, contributed for pharmaceuticals removal. In the presence of P. australis, for paroxetine a 65% removal was observed. Removal increased up to 90% when sediment was present. For bezafibrate, removals reached ca. 47% in P. australis presence, increasing to ca. 70% when nutrients were added to the medium, indicating a good nutritional state can contribute for a higher compound removal. When Cu was added, 75% removal for bezafibrate and 95% removal for paroxetine were observed indicating the metal might influence the removal of the pharmaceuticals. Overall, the plant and its rhizosediments and associated microorganisms showed potential for pharmaceuticals removal from estuaries, eventually degrading the selected compounds, a feature requiring more research. Results indicate that phytoremediation could be a viable option for eliminating/diminishing the environmental impact of pharmaceutical compounds in estuarine areas. [ABSTRACT FROM AUTHOR]

Background: Environmental approaches for minimizing wheat grain Cd are urgently in need in many parts of the world. While metal-removing strategies like phytoextraction or soil-washing are not suitable to the scenario of farmland Cd pollution, rhizoremediation which aims to reduce crops' Cd uptake by using microbial technology has shown great potentials. Methods and results: In this study, a filamentous fungus strain YZ1 was isolated from wheat farmland soil, which is affiliated to Purpureocillium sp. based on morphological and phylogenetical evidence. The strain YZ1 had a minimum inhibitory concentration of 1 mM Cd and was able to survive at 100 mM Cd, with maximum biomass at 0.4 mM Cd. Comparative transcriptomics showed that little changes in cellular transcriptional patterns occurred at 0.4 mM Cd relative to the control, and substantial transcriptional changes could be detected mainly in substance metabolism/transport genes at 2 mM Cd. Pot culture experiments showed that YZ1 rhizo-inoculation ameliorated Cd stress to wheat substantially, leading to a significant reduction by 23.3% to 26.0% in Cd concentration of wheat seedlings. Further, molecular evidence indicated that YZ1 may colonize the wheat root and impact wheat Cd response by modulating wheat's Cd-associated genes, mainly TaEXPA2, TaVP1, TaMRP3, TaPCS1 and TaTM20, while no effect of YZ1 on culture medium pH or Cd bioavailability was observed. Conclusions: A fungal strain YZ1 showing Cd-loving nature was isolated. The strain YZ1 can be a promising candidate for rhizoremediation of Cd-contaminated farmland in wheat-production areas. [ABSTRACT FROM AUTHOR]

Over the past few decades, the exponential growth of the human population, along with the indiscriminate use of pesticides, polycyclic aromatic hydrocarbons, and the discharge of toxic heavy metals and dyes, has had a detrimental impact on the environment. Traditional pollutant mitigation methods pose environmental risks and cause substantial economic costs, often resulting in the generation of hazardous byproducts. In response to these challenges, rhizoremediation has emerged as a promising solution, focusing on the intricate interactions between plants and microbes within the rhizosphere. This comprehensive review aims to identify the dynamics of rhizomicrobiome during bioremediation and emphasize its pivotal role in removing contaminants from the environment. Rhizospheres, a nexus of microbial activity, host diverse bacterial communities that collaborate with plant roots to degrade contaminants efficiently, transform them into less toxic forms, or entrap them. The factors that influence bacterial diversity and function in the rhizosphere are vital for formulating effective strategies and advancing sustainable environmental conservation. This review also provides an overview of recent advancements in omics approaches for studying the rhizomicrobiome and their application to bioremediation. These advances offer insight into the molecular dynamics of plant-microbe interactions to help us better understand bioremediation processes. It is important to understand the dynamics of rhizomicrobiomes during bioremediation, not only to understand better how contaminants are degraded but also to develop conservation strategies that are targeted and efficient for environmental sustainability. The review will serve as a useful compass to mitigate environmental contaminants using the rhizomicrobiome. [Display omitted] • Study of microbial communities in plant roots • Role of rhizomicrobiome in environmental remediation • Efficacy of rhizomicrobiome in sustainable contaminant mitigation • Natural contaminant reduction via rhizomicrobiome • Insights for efficient rhizoremediation strategies. [ABSTRACT FROM AUTHOR]

6:2 Fluorotelomer alcohol (FTOH), one of per- and polyfluoroalkyl substances (PFAS), is widely used as a raw material in synthesizing surfactants and fluorinated polymers. However, little is known about the role of root exudates on 6:2 FTOH biodegradation in the rhizosphere. This study examined the effects of root exudates produced from dicot (Arabidopsis thaliana) and monocot (Brachypodium distachyon) grown under different nutrient conditions (nutrient-rich, sulfur-free, and potassium-free) on 6:2 FTOH biotransformation with or without bioaugmentating agent Rhodococcus jostii RHA1. All the exudates enhanced defluorination of 6:2 FTOH by glucose-grown RHA1. Amendment of dicot or monocot root exudates, regardless of the plant growth conditions, also enhanced 6:2 FTOH biotransformation in soil microcosms. Interestingly, high levels of humic-like substances in the root exudates are linked to high extents of 6:2 FTOH defluorination. Bioaugmenting strain RHA1 along with root exudates facilitated 6:2 FTOH transformation with a production of more diverse metabolites. Microbial community analysis revealed that Rhodococcus was predominant in all strain RHA1 spiked treatments. Different root exudates changed the soil microbiome dynamics. This study provided new insight into 6:2 FTOH biotransformation with different root exudates, suggesting that root exudates amendment and bioaugmentation are promising approaches to promote rhizoremediation for PFAS-contaminated soil. [Display omitted] • Amendment of dicot or monocot root exudates enhanced 6:2 FTOH biotransformation. • Exudates with high humic- and protein-like substances linked to high defluorination. • Amending strain RHA1 and exudates led to production of diverse 6:2 FTOH metabolites. • Root exudates amendment change the microbial communities and diversity. • Rhodococcus is a dominant species in all RHA1 bioaugmented treatments. [ABSTRACT FROM AUTHOR]

Chromium polluted water was increased as the result of the growth of the industries, due to their industrial waste were most likely contain heavy metals, especially textile industrial waste that was discarded to the rivers. This research aimed to study the removal of chromium levels in soil used the symbiosis between plant and bacteria. Soil sample contained with 4.33 mg kg-1 and the irrigation water sample contained with 1.09 mg l-1 of total chromium. This research design was factorial with Randomized Complete Block Design as the based design There were 3 factors in this study: 1. inorganic fertilizer (P): P0: without inorganic fertilizer, P1: with inorganic fertilizer; 2. chelator (B):B0: without chelator, B1: with chelator Rhizobium sp I3, B2: with chelator manure; 3. Plant (T): T0 without plant, T1: with plant. Data were analyzed by statistical analysis using ANOVA continued by T-test or Duncan Multiple Range test and correlation test. The result showed that the remediation process reduced chromium levels in soil with the removal effectivity up to 71.90% on the treatment combination of NPK fertilizer+manure+plant while removal effectivity on plant-only treatment was 55.66%. The chromium levels in Fimbristylis globulosa were in the range from 1.82–3.15 μ g-1, it indicated that Fimbristylis globulosa was a feasible plant for bioremediation. Fimbristylis globulosa grew well and has the ability to absorb chromium, especially by combining it with Rhizobium sp I3and the chromium uptake in roots was higher than shoots.