Phytoremediation of petroleum-contaminated soil by Salicornia: from PSY activity to physiological and morphological communications

Enhancing bioremediation of petroleum-contaminated soil by sophorolipids-modified biochar: Combined metagenomic and metabolomic analyses

In this study, sophorolipids (SLs)-modified biochar (BC-SLs) was used to enhance the bioremediation of petroleum hydrocarbons (PHs) contaminated soil. The biodegradation rate of petroleum hydrocarbons (PHs) by BC-SLs and BC treatments were 62.86 % and 52.64 % after 60 days of remediation experiments, respectively, higher than non-biochar treatment group (24.09 %). The metagenomic analysis showed that the abundance of petroleum-degrading bacteria Actinobacteria and Proteobacteria were increased by 3.8 % and 5.3 %, respectively in BC-SLs treatment, and the abundance of functional genes for PHs degradation, such as alkB, nidA and pcaG, were significantly increased by 12.85 %, 30.08 % and 21.01 %, respectively. The metabolomic analysis showed that BC-SLs facilitated the metabolic process of PHs, the microbial metabolism of petroleum hydrocarbons (PHs) became more active. Fatty acid degradation and polycyclic aromatic hydrocarbons (PAHs) degradation were up-regulated, indicating the promoting effect of the BC-SLs for PHs metabolism. The combined metagenomic and metabolomic analysis demonstrated the strong positive correlations between PHs metabolites and PHs-degrading bacteria, such as lauric acid vs. Actinobacteria, benzoic vs. Proteobacteria. The strong positive correlations between PHs metabolites and PHs-degrading genes were also observed, such as o-ehyltoluene vs. nahD, 4-isopropylbenzoic acid vs. etbAa. The modification of biochar with SLs increased the oxygen-containing functional groups on the surface of biochar. Meanwhile, the emulsification and solubilization of SLs promoted the bioavailability of PHs. The effects of BC-SLs on the nitrogen cycle during PHs remediation showed that it facilitated the accumulation of nitrogen-fixing genes, promoted nitrification but inhibited denitrification process. This study confirms that the application of BC-SLs is an effective remediation of PHs contamination and a sustainable method for controlling agricultural waste resources.

Decrease due to pollution in the rhizosphere microbial diversity can be amended by supplementation from adapted plants of another species

Manipulating the rhizosphere microbiome to enhance plant stress tolerance is an environmentally friendly technology and a renewable resource to restore degraded environments. Here we suggest a sustainable bioremediation strategy on the example of Stebnyk mine tailings storage. We consider Salicornia europaea rhizosphere community, and the ability of the phytoremediation plant Salix viminalis to recruit its beneficial microbiome to mediate the pollution stress at the Stebnyk mine tailings storage. The tailings contain large amounts of brine salts and heavy metals that contaminate the ground water and surrounding areas, changing soil biogeochemistry and causing increased erosion. The species richness of the endophytic bacterial community of S. viminalis roots was assessed based on observed OTUs, Shannon-InvSimpson, and evenness index. Our results obtained using the plant-based enrichment strategy show that biodiversity was decreased across the contamination zones and that S. europaea supplementation significantly increased the species richness. Our results also indicate that the number of dominating bacteria was not changed across zones in both S. europaea-treated and untreated bacterial populations, and that the decrease in richness was mainly caused by the low abundant bacterial OTUs. The importance of selecting the bioremediation strains that are likely to harbor a reservoir of genetic traits that aid in bioremediation function from the target environment is discussed.

Simultaneous bioremediation of diesel-contaminated soil and water ecosystems using mixed culture of Acinetobacter baumannii IITG19 and Providencia vermicola IITG20

Diesel degradation and bacterial growth were investigated in soil, marine water, and freshwater ecosystems using Acinetobacter baumannii IITG19, Providencia vermicola IITG20, and their mixed culture. Both bacteria were found to be effective in all three ecosystems, with the best degradation occurring in freshwater. Acinetobacter baumannii IITG19 showed higher degradation (59%, 62%, and 76%) than Providencia vermicola IITG20 (31%, 57%, and 67%) in soil, marine water, and freshwater, respectively. Alkanes showed higher degradation than naphthenes and aromatics for both strains. The mixed culture showed higher diesel degradation efficiency than individual strains in all ecosystems. The overall degradation was similar in soil and marine water (66%), while freshwater showed the highest degradation of 81%. In the presence of the mixed culture, the degradation of alkanes was more than 90%. Bacterial growth was highest in freshwater and lowest in soil for both bacteria and the mixed culture. Metabolite analysis confirmed alcoholic degradation for alkanes and cyclo-alcoholic degradation for naphthenes. The degradation rate for mixed culture was higher than that of both the individual strains. The mixed culture had highest degradation rate constant in freshwater at 0.11 day-1 followed by that in marine ecosystem at 0.078 day-1. The rate constant was lowest for soil ecosystem at 0.066 day-1. Thus the mixed culture showed effectiveness in all three ecosystems, with its highest effectiveness observed in the freshwater ecosystem.

Overexpressing CsPSY1 Gene of Tea Plant, Encoding a Phytoene Synthase, Improves α-Carotene and β-Carotene Contents in Carrot

Tea plants (Camellia sinensis (L.) O. Kuntze) belong to Theaceae family, in the section Thea. Tea plants are widely distributed in subtropical and tropical regions in the word. α-carotene and β-carotene in the tea leaves belong to carotenoids, which are associated with the aroma and color of the tea. Phytoene synthase (PSY) is a rate-limiting enzyme in carotenoids biosynthesis. We identified three CsPSY genes in 'Shuchazao', named CsPSY1, CsPSY2, and CsPSY3. Structural analysis of three CsPSY genes showed that CsPSY1 had a longer intro structure. The cis-acting elements of CsPSYs promoter were mainly associated with light-responsiveness, abiotic stress-responsiveness, and hormone-responsiveness. CsPSY1 exhibited expression in all tissues of the tea plants, whereas CsPSY2 and CsPSY3 were trace expression levels in all tissues. The positive expression of CsPSY1 under hormonal and abiotic stresses suggested its role in plant development and defense responses. The amino acid sequence of CsPSY1 was highly conserved in eight tea cultivars. The recombinant vector pCAMBIA1301-CsPSY1 was constructed to stabilize the overexpression of CsPSY1 in carrot. The contents of α-carotene and β-carotene in transgenic carrot callus were significantly increased. This study provides a foundational basis for further research on the function of CsPSYs and carotenoids accumulation in tea plants.

The interactions of Cr (VI) concentrations and amendments (biochar and manure) on growth and metal accumulation of two species of Salicornia in contaminated soil

Heavy metals are among the most dangerous contaminants in the environment. Organic components and plant species that can accumulate and stabilize heavy metals in their organs are a good option for soil remediation of these elements. Therefore, this study aimed to investigate the effects of manure and biochar on the accumulation of heavy metals by Salicornia species. Salicornia persica Akhani and Salicornia perspolitana Akhani were cultivated outdoor in experimental pots. The effects of experimental treatments, including Cr (VI) concentrations, manure, and biochar on the two studied species, were investigated. The results indicated a significant effect (p < 0.05) of biochar on the accumulation of heavy metals by two species, S. persica and S. perspolitana, so that Cr concentrations in the roots and shoots were 258 and 5.41 mg/kg, respectively. In addition, Cr accumulations under manure treatments in the roots and shoots were 334.34 and 9.79 mg/kg, respectively. The content of photosynthetic pigments in both S. persica and S. perspolitana species under biochar treatment was higher than in control and manure treatments. In general, one can conclude that the accumulation of Cr in S. perspolitana was higher than in S. persica. Applying biochar and manure amendments could stabilize Cr in soil and reduce Cr accumulation in both S. persica and S. perspolitana species.

Effect of Crude Oil on Growth, Oxidative Stress and Response of Antioxidative System of Two Rye (Secale cereale L.) Varieties

Rye (Secale cereale L.) is one of the most important cereal crops in Eastern and Northern Europe, showing better tolerance to environmental stress factors compared to wheat and triticale. Plant response to the crude oil-polluted soil depends on plant species, oil concentration, time of exposure, etc. The current study is aimed at investigating the growth, oxidative stress and the response of antioxidative system of two rye varieties (Krona and Valdai) cultivated on crude oil-contaminated soils at different concentrations (1.5, 3.0, 6.0, and 12.0%). Inhibition of rye growth was observed at crude oil concentrations of above 3% for above-ground plant parts and of above 1.5% for roots. A decrease in content of chlorophyll a and total chlorophylls in Krona variety was detected at 1.5% oil concentration in soil and in Valdai variety at 3% oil concentration. Compared with the control, the content of malondialdehyde was significantly increased in the Krona variety at 3% oil concentration and in Valdai variety at 6% oil concentration. The crude oil-induced oxidative stress was minimized in rye plants by the enhanced contents of low-molecular antioxidants (proline, non-protein thiols, ascorbic acid, phenolic compounds) and activities of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione peroxidase. The strongest positive correlation was detected between the content of malondialdehyde and contents of proline (r = 0.89–0.95, p ≤ 0.05) and phenolic compounds (r = 0.90–0.94, p ≤ 0.05) as well as superoxide dismutase activity (r = 0.81–0.90, p ≤ 0.05). Based on the results of a comprehensive analysis of growth and biochemical parameters and of the cluster analysis, Valdai variety proved to be more resistant to oil pollution. Due to this, Valdai variety is considered to be a promising rye variety for cultivation on moderately oil-polluted soils in order to decontaminate them. At the same time, it is necessary to conduct further studies aimed at investigating oil transformation processes in the soil-rye system, which would make it possible to determine the efficiency of using this cereal for soil remediation.

Responses and roles of roots, microbes, and degrading genes in rhizosphere during phytoremediation of petroleum hydrocarbons contaminated soil

Rhizodegradation performed by plant roots and the associated bacteria is one of the major mechanisms that contribute to removal of petroleum hydrocarbons (PHCs) during phytoremediation. In this study, the pot-culture experiment using wild ornamental Hylotelephium spectabile (Boreau) H. Ohba was designed to explore responses and roles of roots, microbes, and degrading genes in the rhizodegradation process. Results showed that PHCs degradation rate by phytoremediation was up to 37.6-53.3% while phytoaccumulation accounted for a low proportion, just at 0.3-13.3%. A total of 37 phyla were classified through the high throughput sequencing, among which Proteobacteria, Actinobacteria, and Acidobacteria were the three most dominant phyla, accounting for >60% of the phylum frequency. The selective enrichment of PHC degraders with high salt-tolerance, including Alcanivorax and Bacteroidetes, was induced. Generally, relative abundance of the PHC degrading genes increased significantly with an increase in PHCs concentrations, and the gene copy number in the phytoremediation group was 1.46-14.44 times as much as that in the unplanted controls. Overall, the presence of PHCs and plant roots showed a stimulating effect on the development of specific degraders containing PHC degrading genes, and correspondingly, a biodegradation-beneficial community structure had been constructed to contribute to PHCs degradation in the rhizosphere.