Bioaugmentation with Petroleum-Degrading Consortia Has a Selective Growth-Promoting Impact on Crop Plants Germinated in Diesel Oil-Contaminated Soil

Resuscitation-promoting factors: Novel strategies for the bioremediation of crude oil-contaminated soils

Soil contamination with petroleum hydrocarbons is a major environmental concern. The bioremediation of these soils can be restricted because of the entry of potential microbial degraders into the viable but nonculturable (VBNC) state under unfavorable environmental conditions. Resuscitation agents can stimulate the resuscitation and growth of the bacterial population, improving their degradation capabilities. This study evaluated the efficacy of resuscitation-promoting factor (Rpf) in enhancing the biodegradation of total petroleum hydrocarbons (TPHs) in crude oil-contaminated soils, with a focus on both indigenous and augmented bacterial communities without prior resuscitation. Unlike earlier studies that focused solely on Rpf-treated populations, this study investigated the simultaneous application of Rpf and traditional biostimulation and bioaugmentation processes. Additionally, this work is the first to compare Rpf with other resuscitation agents, including supernatant Rpf (SRpf) and Micrococcus luteus. The results indicated that Rpf-supplemented biostimulation (BS + Rpf) and bioaugmentation (BAS + Rpf) processes achieved 67% and 75% degradation of 31,408 mg kg-1 TPHs within 91 days, respectively, whereas 49% and 64% degradation occured by the BS and BAS processes, respectively. Rpf stimulated the growth of bacterial populations, contributing to enhanced bioremediation of contaminated soil. Furthermore, phytotoxicity decreased with decreasing TPH concentration. These findings also demonstrated that, compared with Rpf, SRpf and M. luteus presented similar TPH removal efficiencies and seemed to be suitable alternatives to recombinant Rpf. These results provide novel insights into the activation of native bacteria by the application of resuscitation agents, demonstrating a promising approach for the bioremediation of crude oil-contaminated soils.

Unlocking bioremediation potential for site restoration: A comprehensive approach for crude oil degradation in agricultural soil and phytotoxicity assessment

Crude oil contamination has inflicted severe damage to soil ecosystems, necessitating effective remediation strategies. This study aimed to compare the efficacy of four different techniques (biostimulation, bioaugmentation, bioaugmentation + biostimulation, and natural attenuation) for remediating agricultural soil contaminated with crude oil using soil microcosms. A consortium of previously characterized bacteria Xanthomonas boreopolis, Microbacterium schleiferi, Pseudomonas aeruginosa, and Bacillus velezensis was constructed for bioaugmentation. The microbial count for the constructed consortium was recorded as 2.04 ± 0.11 × 108 CFU/g on 60 d in augmented and stimulated soil samples revealing their potential to thrive in chemically contaminated-stress conditions. The microbial consortium through bioaugmentation + biostimulation approach resulted in 79 ± 0.92% degradation of the total polyaromatic hydrocarbons (2 and 3 rings ∼ 74%, 4 and 5 rings ∼ 83% loss) whereas, 91 ± 0.56% degradation of total aliphatic hydrocarbons (C8-C16 ∼ 90%, C18-C28 ∼ 92%, C30 to C40 ∼ 88% loss) was observed in 60 d. Further, after 60 d of microcosm treatment, the treated soil samples were used for phytotoxicity assessment using wheat (Triticum aestivum), black chickpea (Cicer arietinum), and mustard (Brassica juncea). The germination rates for wheat (90%), black chickpea (100%), and mustard (100%) were observed in 7 d with improved shoot-root length and biomass in both bioaugmentation and biostimulation approaches. This study projects a comprehensive approach integrating bacterial consortium and nutrient augmentation strategies and underscores the vital role of innovative environmental management practices in fostering sustainable remediation of oil-contaminated soil ecosystems. The formulated bacterial consortium with a nutrient augmentation strategy can be utilized to restore agricultural lands towards reduced phytotoxicity and improved plant growth.

Using Sweet Sorghum Varieties for the Phytoremediation of Petroleum-Contaminated Salinized Soil: A Preliminary Study Based on Pot Experiments

Using energy plants to repair salinized soils polluted by petroleum is an efficient way to solve the problem of farmland reduction and prevent pollutants from entering the food chain simultaneously. In this study, pot experiments were conducted for the purposes of preliminarily discussing the potential of using an energy plant, sweet sorghum (Sorghum bicolor (L.) Moench), to repair petroleum-polluted salinized soils and obtain associated varieties with excellent remediation performance. The emergence rate, plant height and biomass of different varieties were measured to explore the performance of plants under petroleum pollution, and the removal of petroleum hydrocarbons in soil with candidate varieties was also studied. The results showed that the emergence rate of 24 of the 28 varieties were not reduced by the addition of 1.0 × 10⁴ mg/kg petroleum in soils with a salinity of 0.31%. After a 40-day treatment in salinized soil with petroleum additions of 1.0 × 10⁴ mg/kg, 4 potential well-performed varieties including Zhong Ketian No. 438, Ke Tian No. 24, Ke Tian No. 21 (KT21) and Ke Tian No. 6 with a plant height of >40 cm and dry weight of >4 g were screened. Obvious removal of petroleum hydrocarbons in the salinized soils planted with the four varieties were observed. Compared with the treatment without plants, the residual petroleum hydrocarbon concentrations in soils planted with KT21 decreased by 69.3%, 46.3%, 56.5%, 50.9% and 41.4%, for the additions of 0, 0.5 × 10⁴, 1.0 × 10⁴, 1.5 × 10⁴ and 2.0 × 10⁴ mg/kg, respectively. In general, KT21 had the best performance and application potential to remediate petroleum-polluted salinized soil.

Effects of thermal desorption on ecotoxicological characteristics of heavy petroleum-contaminated soil

This study comprehensively evaluates the ecotoxicity of high-concentration heavy petroleum (HCHP)-contaminated soil before and after thermal desorption (TD) remediation at different temperatures and times. The results showed that the detoxification of contaminated soil was effectively achieved by extending the remediation duration at 400-600 °C. After treatment at 400 °C for 60 min, the toxicological indicators including bioluminescence EC₅₀ (acute toxicity), seed germination ratio (Gr) and plant biomass of Brassica juncea (subacute toxicity), and diversity of the microbial community (chronic toxicity) reached a maximum. The value of the SOS-Induction Factor (SOSIF), characterizing genotoxicity was below 1.5, indicating that it was non-toxic. Pearson's correlation analysis illustrated that the water-soluble fraction (WSF), ALK1-3 and ARO1-3 of petroleum hydrocarbons were the primary sources of ecotoxicity. Notably, although the total ratio of petroleum removed from the soil reached 87.26 ± 4.38 %-98.69 ± 1.61 % under high-temperature thermal desorption (HTTD, 500-600 °C), the ecotoxicity was not lower than that at 400 °C. The pyrolysis products of petroleum macromolecules and extreme changes in soil properties were the leading causes of soil ecotoxicity following HTTD. The inconsistency between the removal of petroleum pollutants and ecological health risks reveals the significance of soil ecotoxicological assessments for identifying TD remediation endpoints and process optimization.

Effects of oil contamination on plant growth and development: a review

Oil spills generate several environmental impacts and have become more common with the increase in petroleum extraction, refining, transportation, and trade. In soil, oil contamination increases water and nutrient availability and compaction, directly affecting plant growth and development. Different aspects of phytotoxicity can be observed and will vary according to the characteristics of soil and plants. Oil-contaminated soil also results in negative effects on biomass and changes in leaves and roots. Investigating the effects of oil contamination on plant growth and development can aid in the conservation of plant species and in the development of techniques such as bioremediation and biomonitoring. Thus, this review aims to discuss the main effects of oil contamination on plants, such as environmental stress and morphological, physiological, and anatomical changes, and the strategies developed by plants to survive contamination, as well as to identify plants with phytoremediation potential that can assist in removing oil from the environment.

Control of Seed-Borne Fungi by Selected Essential Oils

Seed-borne pathogens reduce the quality and cause infections at various growth stages of horticultural crops. Some of the best-known are fungi of genus Alternaria, that cause destructive vegetable and other crop diseases, resulting in significant yield losses. Over several years, much attention has been paid to environmentally-friendly solutions for horticultural disease management regarding the environmental damage caused by chemicals. For example, plant extracts and essential oils could be alternative sources for biopesticides and help to control vegetable seed-borne pathogens. This study aimed to evaluate essential oils’ influence on the growth of seed-borne fungi Alternaria spp. The microbiological contamination of vegetable seeds (carrot, tomato, onion) was determined by the agar-plate method. The essential oils’ impact on the growth of fungi was evaluated by mixing them with PDA medium at different amounts. The hydrodistillation was used for extraction of thyme and hyssop essential oils, and common juniper essential oil was purchased. The investigation revealed that the highest contamination of carrot and tomato seeds was by Alternaria spp. fungi. Furthermore, the highest antifungal effect on Alternaria spp. growth was achieved using 200–1000 μL L−1 of thyme essential oil. Meanwhile, the antifungal effect of other investigated essential oils differed from low to moderate. Overall, essential oils expressed a high potential for fungal pathogens biocontrol and application in biopesticides formulations.

Bioaugmentation: possible scenarios due to application of bacterial preparations for remediation of oil-contaminated soil

Although bioaugmentation is known as effective and environmentally friendly method increasing removal of hydrocarbons from oil-contaminated soil, it sometimes fails in soil restoration and disturbs the ecological state of soil. We studied possible scenarios of the introduction of oil-degrading bacteria into oil-contaminated podzolic soil assessing the environmental safety of different bacterial preparations in a long-term field experiment. Integral indicators characterizing the state of biocenosis included biological activity of soil and aboveground biomass of grasses. It has been established that bacterial preparations can have both positive and negative effects on the ecological state of soil and oil biodegradation. Of the five bacterial preparations studied, one had a pronounced positive effect on soil biological activity and oil mineralization processes. Two preparations did not accelerate oil biodegradation and were characterized by a weaker positive effect or even a lack of influence. Two more bacterial preparations had a significant negative impact on soil biological properties. These preparations slowed oil mineralization in soil. Both positive and negative effects of bacterial preparations were observed only during the first two years after their application. All preparations were not effective during the latter stages of long-term remediation processes. The results indicate that successful application of bioaugmentation for the restoration of oil-contaminated soil requires testing of environmental safety of bacterial preparations in a long-term field experiments prior to any treatment processes.

Isolation and Characterization of Oil-Degrading Enterobacter sp. from Naturally Hydrocarbon-Contaminated Soils and Their Potential Use against the Bioremediation of Crude Oil

The contamination of crude oil in soil matrices is a persistent problem with negative repercussions because of the recalcitrant, hazardous, and mutagenic properties of its constituents. To mitigate the effect of crude oil contamination in soil, the use of microorganisms is a cheap and feasible option. In the current study, bacterial species from numerous polluted oil field surfaces were isolated and examined for their ability to degrade crude oil. Random soil samples polluted with hydrocarbons were collected and various bacterial isolates were isolated. Results revealed that 40% of total isolates had potential use for hydrocarbon biodegradation, the synthesis of exopolysaccharides and the solubilization of phosphorous. Following isolation and characterization to degrade crude oil, a pot trial was conducted using maize inoculated with the four best strains—i.e., S1 (PMEL-63), S2 (PMEL-67), S3 (PMEL-80), and S4 (PMEL-79)—in artificially hydrocarbon-polluted soil with concentrations of crude oil of 0, 1000, and 2000 ppm. Results revealed that S4 (PMEL-79) had significant potential to degrade hydrocarbon in polluted soils. The root length, shoot length, and fresh biomass of maize were increased by 65%, 45%, and 98%, respectively, in pots inoculated with S4 (PMEL-79) Enterobacter cloacae subsp., whereas the lowest root length was observed where no strain was added and the concentration of crude oil was at maximum. Moreover, S4 (PMEL-79) Enterobacter cloacae subsp. was found to be the most effective strain in degrading crude oil and increasing maize growth under polluted soil conditions. It was concluded that the isolation of microorganisms from oil-contaminated sites should be considered in order to identify the most effective microbial consortium for the biodegradation of naturally hydrocarbon-contaminated soils.

Functional potential of sewage sludge digestate microbes to degrade aliphatic hydrocarbons during bioremediation of a petroleum hydrocarbons contaminated soil

Sewage sludge digestate is a valuable organic waste which can be used as fertilizer in soil bioremediation. Sewage sludge digestate is not only a good source of nutrients but is also rich in bacteria carrying alkB genes, which are involved in aliphatic hydrocarbons metabolism. Increase of alkB genes ratio in polluted soils has been observed to improve bioremediation efficiency. In this study, for the first time, the genetic potential of indigenous microorganisms of digestate to degrade petroleum products was assessed. The objectives were to study petroleum hydrocarbons (PHCs) removal together with shifts in soil taxa and changes in the concentration of alkB genes after digestate application. Initial alkB genes concentration in contaminated soils and digestate was 1.5% and 4.5%, respectively. During soil incubation with digestate, alkB genes percentage increased up to 11.5% and after the addition of bacteria immobilized onto biochar this value increased up to 60%. Application of digestate positively affected soil respiration and bacterial density, which was concomitant with enhanced PHCs degradation. Incubation of soil amended with digestate resulted in 74% PHCs decrease in 2 months, while extra addition of bacteria immobilized onto biochar increased this value up to 95%. The use of digestate affected the microbial community profiles by increasing initial bacterial density and diversity, including taxa containing recognized PHCs degraders. This study reveals the great potential of digestate as a soil amendment which additionally improves the abundance of alkB genes in petroleum contaminated soils.

Novel esterquat-based herbicidal ionic liquids incorporating MCPA and MCPP for simultaneous stimulation of maize growth and fighting cornflower

Modern agricultural practices are often based on the use of mixtures of specific herbicides to achieve efficient crop protection. The major drawbacks of commercial herbicidal formulations include the necessity to incorporate toxic surfactants and high volatility of active substances. Transformation of herbicides into herbicidal ionic liquids (HILs) seems to be a promising alternative which allows to almost completely reduce volatility due to ionic interactions. In the scope of this research, we transformed (2-methyl-4-chlorophenoxy)acetic acid (MCPA) into a quaternary ester (esterquat) with the use of derivatives of 2-dimethylaminoethanol. The obtained esterquats were later coupled with (±)-2-(4-chloro-2-methylphenoxy)propionic acid (MCPP) in the form of an anion. The combination of MCPA and MCPA is commonly applied in the UK, EU countries and also in the USA to increase the spectrum of targeted weed species. In the framework of this study, novel HILs with an esterquat moiety incorporating a long alkyl chain (C₈, C₉, C₁₀, C₁₁, C₁₂, C₁₄) were prepared and characterized in terms of basic physicochemical properties (solubility and volatility) as well as biodegradability. Their phytotoxicity was assessed towards cornflower (Centaurea cyanus) as a model weed and maize (Zea mays) as a crop plant. The presence of the esterquat cation contributed to satisfactory solubility in water and other low polar solvents, which eliminates the need to add exogenous adjuvants. Further experiments indicated that the tested HILs stimulated the germination stage of maize and maintained high herbicidal activity towards cornflower. No significant differences in terms of properties were observed in case of HILs which included alkyl substituents with an odd number of carbon atoms. Future studies should be focused on structural modifications in order to improve the biodegradability as well as field studies for evaluation of commercial applications.

Rhizoremediation as a green technology for the remediation of petroleum hydrocarbon-contaminated soils

Rhizoremediation is increasingly becoming a green and sustainable alternative to physico-chemical methods for remediation of contaminated environments through the utilization of symbiotic relationship between plants and their associated soil microorganisms in the root zone. The overall efficiency can be enhanced by identifying suitable plant-microbe combinations for specific contaminants and supporting the process with the application of appropriate soil amendments. This approach not only involves promoting the existing activity of plants and soil microbes, but also introduces an adequate number of microorganisms with specific catabolic activity. Here, we reviewed recent literature on the main mechanisms and key factors in the rhizoremediation process with a particular focus on soils contaminated with total petroleum hydrocarbon (TPH). We then discuss the potential of different soil amendments to accelerate the remediation efficiency based on biostimulation and bioaugmentation processes. Notwithstanding some successes in well-controlled environments, rhizoremediation of TPH under field conditions is still not widespread and considered less attractive than physico-chemical methods. We catalogued the major pitfalls of this remediation approach at the field scale in TPH-contaminated sites and, provide some applicable situations for the future successful use of in situ rhizoremediation of TPH-contaminated soils.

Enhanced Growth of Mungbean and Remediation of Petroleum Hydrocarbons by Enterobacter sp. MN17 and Biochar Addition in Diesel Contaminated Soil

Petroleum hydrocarbon (PHC) contamination of soil is a widespread global environmental concern due to the persistence and recalcitrant nature of PHCs. The PHCs are highly toxic and their removal from the terrestrial ecosystem is necessary to maintain soil as well as human health. Here, a pot experiment was performed to examine the impact of Enterobacter sp. MN17 and biochar addition on the growth of mungbean plants and PHCs removal from diesel-polluted soil. For this purpose, soil was contaminated artificially with diesel to achieve a final concentration of 5000 mg kg−1. Untreated and Enterobacter sp. MN17 treated mungbean seeds were sown in pots. Sugarcane bagasse biochar was applied as an amendment in respective pots along with the recommended levels of essential nutrients. Results showed that PHCs significantly suppressed the seedling emergence as well as agronomic and physiological attributes of mungbean as compared to un-contaminated controls. However, the co-application of Enterobacter sp. MN17 and biochar significantly reduced the phytotoxicity of PHCs to mungbean plants and effectively increased the seedling emergence, shoot and root length, shoot fresh and dry biomass, root fresh and dry biomass of plants up to 24%, 54%, 52%, 52%, 54%, 55% and 60%, respectively as compared to controls. Similarly, 30%, 57%, 64%, 36% and 57% increase in chlorophylls contents, transpiration rate, stomatal conductance, sub-stomatal conductance, and photosynthetic rate, respectively were observed in their combined application as compared to respective controls. Furthermore, the co-addition of biochar and Enterobacter sp. MN17 could remove 69% and 85% higher PHCs from unplanted and planted pots, respectively, than that of their respective controls. Our results suggest that the co-application of biochar and Enterobacter sp. MN17 may be useful in enhancing plant growth and eliminating PHCs from contaminated soil.

A newly isolated strain of Serratia sp. from an oil spillage site of Assam shows excellent bioremediation potential

A hydrocarbon-degrading strain was isolated from a petroleum oil-contaminated site which was identified on the basis of 16S rDNA gene sequencing as a member of the genus Serratia. The isolate reduced surface tension of petroleum oil supplemented medium by 48.35% with respect to control after 7 days of treatment. Fluorescence microscopy revealed that its chemotaxis was towards hydrocarbon. The isolate degraded 87.54 and 85.48% of diesel and kerosene in liquid culture, respectively, after 28 day incubation at 37 ± 2 °C. The ex situ pilot scale bioremediation experiment in which artificially contaminated soil (10 and 20% v/w kerosene) was treated for 7 days showed a germination rate of Vigna radiate seeds of 52% and 72%, respectively. Interestingly, a germination rate of 31% was obtained with the heavily contaminated soil samples collected from the oil spillage site after 20 days of bioremediation treatment. The presence of υ_CH3 (asymmetric stretching), υ_C=C (stretch), and υ_C-C (stretch) in the crude biosurfactant produced by the isolate was revealed by FTIR analysis, and emulsification index (E ₂₄) was found 60 and 56.6%, respectively, against diesel and kerosene oil. The non-cytotoxicity nature of the biosurfactant also supports its potential application in field trial.

Bioremediation of Polluted Soil Sites with Crude Oil Hydrocarbons Using Carrot Peel Waste

The biostimulation potentials of carrot peel waste and carob kibbles for bioremediation of crude petroleum-oil polluted soil were investigated. Temperature, pH, moisture, total petroleum hydrocarbon (TPH), and changes in microbial counts during 45 days were monitored when 4 mL of carrot peel waste or carob kibbles media were added to 200 g of crude oil polluted soil samples. Gas chromatography-flame ionization detection (GC-FID) was used to compare hydrocarbon present in the crude oil polluted soil and in pure fuel, composition of crude oil polluted soil was analyzed by X-ray diffraction (XRD), and the TPH was measured by distillation using distiller mud. The results showed that, at the end of experiments, the concentration of TPH decreased in crude oil polluted soil containing carrot peel waste with a percentage of 27 ± 1.90% followed by crude oil polluted soil containing carob kibbles (34 ± 1.80%) and in the unamended control soil (36 ± 1.27%), respectively. The log [Colony Forming Unit (CFU)/g] of total heterotrophic bacteria in the crude oil polluted soil increased from 10.46 ± 0.91 to 13.26 ± 0.84 for carrot peel waste, from 11.01 ± 0.56 to 11.99 ± 0.77 for carob kibbles and from 8.18 ± 0.39 to 8.84 ± 0.84 for control, respectively. Such results demonstrated that carrot peel could be used to enhance activities of the microbial hydrocarbon-degrading bacteria during bioremediation of crude petroleum-oil polluted soil.

Remediation of saline soils contaminated with crude oil using the halophyte Salicornia persica in conjunction with hydrocarbon-degrading bacteria

The negative impact of salinity on plant growth and the survival of rhizosphere biota complicates the application of bioremediation to crude oil-contaminated saline soils. Here, a comparison was made between the remedial effect of treating the soil with Pseudomonas aeruginosa, a salinity tolerant hydrocarbon-degrading consortium in conjunction with either the halophyte Salicornia persica or the non-halophyte Festuca arundinacea. The effect of the various treatments on salinized soils was measured by assessing the extent of total petroleum hydrocarbon (TPH) degradation, the soil's dehydrogenase activity, the abundance of the bacteria and the level of phytotoxicity as measured by a bioassay. When a non-salinized soil was assessed after a treatment period of 120 days, the ranking for effectiveness with respect to TPH removal was F. arundinacea > P. aeruginosa > S. persica > no treatment control, while in the presence of salinity, the ranking changed to S. persica > P. aeruginosa > F. arundinacea > no treatment control. Combining the planting of S. persica or F. arundinacea with P. aeruginosa inoculation ("bioaugmentation") boosted the degradation of TPH up to 5-17%. Analyses of the residual oil contamination revealed that long chain alkanes (above C20) were particularly strongly degraded following the bioaugmentation treatments. The induced increase in dehydrogenase activity and the abundance of the bacteria (3.5 and 10 fold respectively) achieved in the bioaugmentation/S. persica treatment resulted in 46-76% reduction in soil phytotoxicity in a saline soil. The indication was that bioaugmentation of halophyte can help to mitigate the adverse effects on the effectiveness of bioremediation in a crude oil-contaminated saline soil.

Study of microbial diversity in plant-microbe interaction system with oil sludge contamination

A 90 days greenhouse experiment was conducted for evaluation of soil microbial diversity in different treatments of rhizospheric and nonrhizospheric oil sludge contaminated soil. Various pot treatments (T1-T5) were as follows: 2% oil sludge contaminated soil was considered as control (T1); augmentation of control with preadapted microbial consortium was T2; addition of Vetiver zizanioide to control was T3; bioaugmentation of control along with V. zizanioide was T4; and bioaugmentation with V. zizanioide and bulking agent was T5. During the study, different microbial populations were determined in all treatments. Additionally, soil microbial diversity using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) of 16S rDNA was carried out. At the end of experimental period, significant increase in microbial number in bioaugmented rhizospheric treatments (T4 and T5) was observed as compared to non-rhizospheric and non-bioaugmented treatments (T2 and T3). The community and sequencing results revealed that combined treatment of plant and microbes resulted in improved microbial species and number. The dominant phyla belonged to γ proteobacteria, β proteobacteria, Chloroflexi, firmicutes, and uncultured bacteria. It is concluded that plant-microbe-soil system supports immense oil degrading microbial diversity and can be used as an effective indicator tool for remediation of oil sludge contaminated sites.

Esterquat herbicidal ionic liquids (HILs) with two different herbicides: evaluation of activity and phytotoxicity

Novel weed control agents in the form of herbicidal ionic liquids comprising two different herbicides as a cation and an anion.

A review of germination and early growth as a proxy for plant fitness under petrogenic contamination - knowledge gaps and recommendations

Germination-an important stage in the life cycle of plants-is susceptible to the presence of soil contaminants. Since the early 1990s, the use of germination tests to screen multiple plant species to select candidates for phytoremediation has received much attention. This is due to its inexpensive methodology and fast assessment relative to greenhouse or field growth studies. Surprisingly, no comprehensive synthesis is available of these studies in the scientific literature. As more plant species are added to phytoremediation databases, it is important to encapsulate the knowledge thus far and revise protocols. In this review, we have summarised previously-documented effects of petroleum hydrocarbons on germination and seedling growth. The methods and materials of previous studies are presented in tabulated form. Common practice includes the use of cellulose acetate filter paper, plastic Petri dishes, and low numbers of seeds and replicates. A general bias was observed for the screening of cultivated crops as opposed to native species, even though the latter may be better suited to site conditions. The relevance of germination studies as important ecotoxicological tools is highlighted with the proposed use of root imaging software. Screening of novel plant species, particularly natives, is recommended with selection focussed on (i) species phylogeny, (ii) plant morphological and functional traits, and (iii) tolerance towards harsh environmental stresses. Recommendations for standardised protocols for germination and early growth monitoring are made in order to improve the robustness of statistical modelling and species selection in future phytoremediation evaluations and field programs.

Assessment of hydrocarbon degradation potentials in a plant-microbe interaction system with oil sludge contamination: A sustainable solution

A pot culture experiment was conducted for 90 days for the evaluation of oil and total petroleum hydrocarbon (TPH) degradation in vegetated and non-vegetated treatments of real-field oil-sludge-contaminated soil. Five different treatments include (T1) control, 2% oil-sludge-contaminated soil; (T2), augmentation of microbial consortium; (T3), Vertiveria zizanioides; (T4), bio-augmentation along with V. zizanioides; and (T5), bio-augmentation with V. zizanioides and bulking agent. During the study, oil reduction, TPH, and degradation of its fractions were determined. Physico-chemical and microbiological parameters of soil were also monitored simultaneously. At the end of the experimental period, oil content (85%) was reduced maximally in bio-augmented rhizospheric treatments (T4 and T5) as compared to control (27%). TPH reduction was observed to be 88 and 89% in bio-augmented rhizospheric soil (T4 and T5 treatments), whereas in non-rhizospheric and control (T2 and T1), TPH reduction was 78 and 37%, respectively. Degradation of aromatic fraction after 90 days in bio-augmented rhizosphere of treatments T4 and T5 was found to 91 and 92%, respectively. In microbial (T2) and Vertiveria treatments (T3), degradation of aromatic fraction was 83 and 68%, respectively. A threefold increase in soil dehydrogenase activity and noticeable changes in organic carbon content and water-holding capacity were also observed which indicated maximum degradation of oil and its fractions in combined treatment of plants and microbes. It is concluded that the plant-microbe soil system helps to restore soil quality and can be used as an effective tool for the remediation of oil-sludge-contaminated sites.

The responses of two native plant species to soil petroleum contamination in the Yellow River Delta, China

Petroleum contamination is a significant environmental problem in the Yellow River Delta. The responses of two native salt-tolerant plant species, alfalfa (Medicago sativa) and bristle grass (Setaria uiridis Beauv), to soil petroleum contamination were investigated at five levels between 0 and 2.0% (w/w). Results showed that the total, aboveground and underground plant biomasses of both species were significantly reduced by petroleum contamination (p < 0.05), with the inhibition enhanced with increased petroleum levels. However, the emergence rate of bristle grass was promoted by petroleum contamination. Following 100 days of exposure, the number of soil petroleum degraders increased greatly, with a trend of initial increase followed by a decrease at 1.5% contamination or higher. Compared to bulk soils, bacteria-degrading alkanes, total hydrocarbons and PAHs in alfalfa rhizosphere soils increased by 1.33-4.18-, 0.85-3.01- and 4.12-12.75-fold, respectively, with an increase of 2.80-10.00-, 4.42-14.44- and 7.30-26.00-fold in bristle grass rhizosphere soils, respectively. The greatest number of petroleum degraders in bristle grass rhizosphere soils resulted in the highest petroleum degradation rate. Bristle grass may be the optimal species for petroleum remediation in the studied area.

Rhizoremediation of cadmium-contaminated soil associated with hydroxamate siderophores isolated from Cd-resistant plant growth-promoting Dietzia maris and Lysinibacillus strains

In search of multitrait plant growth-promoting (PGP) inoculants, we introduced two cadmium-resistant bacterial strains, C4 (PG), C5 (WB), and their consortium C6 (PG × WB) isolated from metal-contaminated industrial waste-fed canal near West Bengal. The test isolates were biochemically characterized and screened in vitro for siderophore production. The infrared spectra revealed the hydroxamate nature of the siderophore produced. Further in green house, siderophore-based seed inoculation with selected PGP isolates exhibited stimulatory effects on seed germination (up to 85.4%), chlorophyll index (22.9 spad unit), shoot and root length (70% and 62.7%), tiller numbers (38.82%), spikelet numbers (52.2%), straw yield (62.2%), grain yield (76.1%), total dry matter of root and shoot (55.56% and 64.4%, respectively), and grain yields (76.1%) of tested wheat cultivars. The 16S rRNA sequencing identified strain PG and WB as Dietzia maris and Lysinibacillus sp. strains. Furthermore, inoculation of C6 (consortium) in both cultivar UP-2565 and KS-227 showed maximum Cd sorption capacity in roots (38.3% and 67.1%) and shoots (68.4% and 67.5%), respectively. Both the strains and their consortium showed a great potential to increase the growth and yield of wheat cultivars, which can also be utilized for rhizoremediation process.

The Interaction between Plants and Bacteria in the Remediation of Petroleum Hydrocarbons: An Environmental Perspective

Widespread pollution of terrestrial ecosystems with petroleum hydrocarbons (PHCs) has generated a need for remediation and, given that many PHCs are biodegradable, bio- and phyto-remediation are often viable approaches for active and passive remediation. This review focuses on phytoremediation with particular interest on the interactions between and use of plant-associated bacteria to restore PHC polluted sites. Plant-associated bacteria include endophytic, phyllospheric, and rhizospheric bacteria, and cooperation between these bacteria and their host plants allows for greater plant survivability and treatment outcomes in contaminated sites. Bacterially driven PHC bioremediation is attributed to the presence of diverse suites of metabolic genes for aliphatic and aromatic hydrocarbons, along with a broader suite of physiological properties including biosurfactant production, biofilm formation, chemotaxis to hydrocarbons, and flexibility in cell-surface hydrophobicity. In soils impacted by PHC contamination, microbial bioremediation generally relies on the addition of high-energy electron acceptors (e.g., oxygen) and fertilization to supply limiting nutrients (e.g., nitrogen, phosphorous, potassium) in the face of excess PHC carbon. As an alternative, the addition of plants can greatly improve bioremediation rates and outcomes as plants provide microbial habitats, improve soil porosity (thereby increasing mass transfer of substrates and electron acceptors), and exchange limiting nutrients with their microbial counterparts. In return, plant-associated microorganisms improve plant growth by reducing soil toxicity through contaminant removal, producing plant growth promoting metabolites, liberating sequestered plant nutrients from soil, fixing nitrogen, and more generally establishing the foundations of soil nutrient cycling. In a practical and applied sense, the collective action of plants and their associated microorganisms is advantageous for remediation of PHC contaminated soil in terms of overall cost and success rates for in situ implementation in a diversity of environments. Mechanistically, there remain biological unknowns that present challenges for applying bio- and phyto-remediation technologies without having a deep prior understanding of individual target sites. In this review, evidence from traditional and modern omics technologies is discussed to provide a framework for plant-microbe interactions during PHC remediation. The potential for integrating multiple molecular and computational techniques to evaluate linkages between microbial communities, plant communities and ecosystem processes is explored with an eye on improving phytoremediation of PHC contaminated sites.

Degradation of phenanthrene by Novosphingobium sp. HS2a improved plant growth in PAHs-contaminated environments

At the same time that the European Union (EU) policy recommend to direct efforts towards reductions of heavy metals, polycyclic aromatic hydrocarbons (PAHs) and mining residues, there is the need to increase the cultivable areas within Europe to cope with the increasing demands for food and energy crops. Bioremediation is a good technique for the restoration of contaminated soils; however, it has not been used extensively because of the variability of the outcome. This variability is frequently due to a bad establishment of foreign degrading populations in soil. We have demonstrated that Novosphingobium sp. HS2aR (i) is able to compete with other root colonizers and with indigenous bacteria, (ii) is able to establish in high numbers in the contaminated environments and (iii) is able to remove more than 90 % of the extractable phenanthrene in artificially contaminated soils. Furthermore, we have demonstrated that the capacity to remove phenanthrene is linked to the ability to promote plant growth in contaminated environments. The fact that the presence of Novosphingobium sp. HS2aR improves the growth of plants in contaminated soil suggests that it may be a useful strain for utilization in amelioration of soil quality while improving the growth of economically important energy crops, thus adding value to the bioremediation strategy.

Bioremediation of petroleum contaminated soil to combat toxicity on Withania somnifera through seed priming with biosurfactant producing plant growth promoting rhizobacteria

Soil contaminated by Petroleum oil cannot be utilized for agricultural purposes due to hydrocarbon toxicity. Oil contaminated soil induces toxicity affecting germination, growth and productivity. Several technologies have been proposed for bioremediation of oil contaminated sites, but remediation through biosurfactant producing plant growth promontory rhizobacteria (PGPR) is considered to be most promising methods. In the present study the efficacy of seed priming on growth and pigment of Withania somnifera under petroleum toxicity is explored. Seeds of W. somnifera were primed with biosurfactant producing Pseudomonas sp. AJ15 with plant growth promoting traits having potentiality to utilized petroleum as carbon source. Results indicates that plant arose from priming seeds under various petroleum concentration expressed high values for all the parameters studied namely germination, shoot length, root length, fresh and dry weight and pigments (chlorophyll and carotenoid) as compared to non primed seed. Hence, the present study signifies that petroleum degrarding biosurfactant producing PGPR could be further used for management and detoxification of petroleum contaminated soils for growing economically important crops.

The response of maize (Zea mays L.) plant assisted with bacterial consortium and fertilizer under oily sludge

The objective of this study was to evaluate the role of PGPR consortium and fertilizer alone and in combination on the physiology of maize grown under oily sludge stress environment as well on the soil nutrient status. Consortium was prepared from Bacillus cereus (Acc KR232400), Bacillus altitudinis (Acc KF859970), Comamonas (Delftia) belonging to family Comamonadacea (Acc KF859971) and Stenotrophomonasmaltophilia (Acc KF859973). The experiment was conducted in pots with complete randomized design with four replicates and kept in field. Oily sludge was mixed in ml and Ammonium nitrate and Diammonium phosphate (DAP) were added at 70 ug/g and 7 ug/g at sowing. The plant was harvested at 21 d for estimation of protein, proline and antioxidant enzymes superoxide dismutase (SOD) and peroxidase (POD). To study the degradation, total petroleum hydrocarbon was extracted by soxhelt extraction and extract was analyzed by GC-FID at different period after incubation. Combined application of consortium and fertilizer enhanced the germination %, protein and, proline content by 90,130 and 99% higher than untreated maize plants. Bioavailability of macro and micro nutrient was also enhanced with consortium and fertilizer in oily sludge. The consortium and fertilizer in combined treatment decreased the superoxide dismutase (SOD), peroxidase dismutase (POD) of the maize leaves grown in oily sludge. Degradation of total petroleum hydrocarbon (TPHs) was 59% higher in combined application of consortium and fertilizer than untreated maize at 3 d. The bacterial consortium can enhanced the maize tolerance to oily sludge and enhanced degradation of total petroleum hydrocarbon (TPHs). The maize can be considered as tolerant plant species to remediate oily sludge contaminated soils.

Enrichment of aliphatic, alicyclic and aromatic acids by oil-degrading bacteria isolated from the rhizosphere of plants growing in oil-contaminated soil from Kazakhstan

Three microbial strains were isolated from the rhizosphere of alfalfa (Medicago sativa), grass mixture (Festuca rubra, 75 %; Lolium perenne, 20 %; Poa pratensis, 10 %), and rape (Brassica napus) on the basis of their high capacity to use crude oil as the sole carbon and energy source. These isolates used an unusually wide spectrum of hydrocarbons as substrates (more than 80), including n-alkanes with chain lengths ranging from C12 to C32, monomethyl- and monoethyl-substituted alkanes (C12-C23), n-alkylcyclo alkanes with alkyl chain lengths from 4 to 18 carbon atoms, as well as substituted monoaromatic and diaromatic hydrocarbons. These three strains were identified as Gordonia rubripertincta and Rhodococcus sp. SBUG 1968. During their transformation of this wide range of hydrocarbon substrates, a very large number of aliphatic, alicyclic, and aromatic acids was detected, 44 of them were identified by GC/MS analyses, and 4 of them are described as metabolites for the first time. Inoculation of plant seeds with these highly potent bacteria had a beneficial effect on shoot and root development of plants which were grown on oil-contaminated sand.

Effect of plant growth-promoting bacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) inoculation on oats in saline-alkali soil contaminated by petroleum to enhance phytoremediation

To investigate the effect of plant growth-promoting bacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) on phytoremediation in saline-alkali soil contaminated by petroleum, saline-alkali soil samples were artificially mixed with different amount of oil, 5 and 10 g/kg, respectively. Pot experiments with oat plants (Avena sativa) were conducted under greenhouse condition for 60 days. Plant biomass, physiological parameters in leaves, soil enzymes, and degradation rate of total petroleum hydrocarbon were measured. The result demonstrated that petroleum inhibited the growth of the plant; however, inoculation with PGPR in combination with AMF resulted in an increase in dry weight and stem height compared with noninoculated controls. Petroleum stress increased the accumulation of malondialdehyde (MDA) and free proline and the activities of the antioxidant enzyme such as superoxide dismutase, catalase, and peroxidase. Application of PGPR and AMF augmented the activities of three enzymes compared to their respective uninoculated controls, but decreased the MDA and free proline contents, indicating that PGPR and AMF could make the plants more tolerant to harmful hydrocarbon contaminants. It also improved the soil quality by increasing the activities of soil enzyme such as urease, sucrase, and dehydrogenase. In addition, the degradation rate of total petroleum hydrocarbon during treatment with PGPR and AMF in moderately contaminated soil reached a maximum of 49.73%. Therefore, we concluded the plants treated with a combination of PGPR and AMF had a high potential to contribute to remediation of saline-alkali soil contaminated with petroleum.

Rhizoremediation of diesel-contaminated soil with two rapeseed varieties and petroleum degraders reveals different responses of the plant defense mechanisms

Plant-assisted bioremediation (rhizoremediation) stands out as a potential tool to inactivate or completely remove xenobiotics from the polluted environment. Therefore, it is of key importance to find an adequate combination of plant species and microorganisms that together enhance the clean-up process. To understand the response of plants upon bioaugmentation, the antioxidative and detoxification system was analyzed in high and low erucic acid rapeseed varieties (HEAR and LEAR, respectively), after 8 weeks of their treatment with petroleum degraders and 6000 mg diesel oil/kg dry soil. The oxidative stress was enhanced in LEAR being exposed to sole diesel oil, in comparison with HEAR. However, when LEAR plants were additionally inoculated with bacteria, suppression of total catalase (CAT) and ascorbate peroxidase (APX) activity were observed. Interestingly, glutathione transferase (GST) activity was found in these plants at a much higher level than in HEAR, which correlated with a more efficient diesel removal performed by LEAR in the polluted soil and upon bioaugmentation. A distinct profile of polycyclic aromatic hydrocarbons (PAH) was detected in leaves of these plants. Neither LEAR nor HEAR experienced any changes in the photosynthetic capacity upon diesel pollution and presence of petroleum degraders, which supports the usefulness of rhizoremediation with rapeseed.