Phenanthrene-Degrading and Nickel-Resistant Neorhizobium Strain Isolated from Hydrocarbon-Contaminated Rhizosphere of Medicago sativa L.

Pollutant degradation and heavy-metal resistance may be important features of the rhizobia, making them promising agents for environment cleanup biotechnology. The degradation of phenanthrene, a three-ring polycyclic aromatic hydrocarbon (PAH), by the rhizobial strain Rsf11 isolated from the oil-polluted rhizosphere of alfalfa and the influence of nickel ions on this process were studied. On the basis of whole-genome and polyphasic taxonomy, the bacterium Rsf11 represent a novel species of the genus Neorhizobium, so the name Neorhizobium phenanthreniclasticum sp. nov. was proposed. Analysis of phenanthrene degradation by the Rsf1 strain revealed 1-hydroxy-2-naphthoic acid as the key intermediate and the activity of two enzymes apparently involved in PAH degradation. It was also shown that the nickel resistance of Rsf11 was connected with the extracellular adsorption of metal by EPS. The joint presence of phenanthrene and nickel in the medium reduced the degradation of PAH by the microorganism, apparently due to the inhibition of microbial growth but not due to the inhibition of the activity of the PAH degradation enzymes. Genes potentially involved in PAH catabolism and nickel resistance were discovered in the microorganism studied. N. phenanthreniclasticum strain Rsf11 can be considered as a promising candidate for use in the bioremediation of mixed PAH-heavy-metal contamination.

Natural and Technical Phytoremediation of Oil-Contaminated Soil.

Natural and technical phytoremediation approaches were compared for their efficacy in decontaminating oil-polluted soil. We examined 20 oil-contaminated sites of 800 to 12,000 m2 each, with different contamination types (fresh or aged) and levels (4.2-27.4 g/kg). The study was conducted on a field scale in the industrial and adjacent areas of a petroleum refinery. Technical remediation with alfalfa (Medicago sativa L.), ryegrass (Lolium perenne L.), nitrogen fertilizer, and soil agrotechnical treatment was used to clean up 10 sites contaminated by oil hydrocarbons (average concentration, 13.7 g/kg). In technical phytoremediation, the per-year decontamination of soil was as high as 72-90%, whereas in natural phytoremediation (natural attenuation with native vegetation) at 10 other oil-contaminated sites, per-year decontamination was as high as that only after 5 years. Rhizodegradation is supposed as the principal mechanisms of both phytoremediation approaches.

Study of Boraginaceae plants for phytoremediation of oil-contaminated soil.

Long-term field observations of the natural vegetation cover in industrial and adjacent areas has revealed that the Boraginaceae was one of the main plant family representatives of which were noted in oil-contaminated area. In this study against the background of the previously well characterized plant families Poaceae and Fabaceae, the phytoremediation potential of Boraginaceae plants was investigated under the field conditions and described. Among the members of this family, Lithospermum arvense, Nonea pulla, Asperugo procumbens, Lappula myosotis, and Echium vulgare were the most common in oil-contaminated areas. N. pulla was the most tolerant to hydrocarbons and, along with L. arvense and E. vulgare, actively stimulated the soil microorganisms, including hydrocarbon-oxidizing ones, in their rhizosphere. A comparative assay confirmed that the plants of the Fabaceae family as a whole more efficiently enrich the soil both with available nitrogen and with pollutant degradation genes. Nevertheless, the comparatively high ammonium nitrogen content in the rhizosphere of N. pulla and E. vulgare allows these species to be singled out to explain their high rhizosphere effect, and to suggest their remediation potential for oil-contaminated soil.Novelty statement Against the background of the previously well characterized plant families Poaceae and Fabaceae, the remediation potential of Boraginaceae plants was described for the first time. Overall, this study contributes to understanding the differences in remediation potential of plants at the family level and suggests the monitoring pollutant degradation genes as an informative tool to the search for plant promising for use in the cleanup of oil-contaminated soil.

Physiological and biochemical characteristic of Miscanthus × giganteus grown in heavy metal - oil sludge co-contaminated soil.

The effect of oil sludge and zinc, present in soil both separately and as a mixture on the physiological and biochemical parameters of Miscanthus × giganteus plant was examined in a pot experiment. The opposite effect of pollutants on the accumulation of plant biomass was established: in comparison with uncontaminated control the oil sludge increased, and Zn reduced the root and shoot biomass. Oil sludge had an inhibitory effect on the plant photosynthetic apparatus, which intensified in the presence of Zn. The specific antioxidant response of M. × giganteus to the presence of both pollutants was a marked increase in the activity of superoxide dismutase (mostly owing to oil sludge) and glutathione-S-transferase (mostly owing to zinc) in the shoots. The participation of glutathione-S-transferase in the detoxification of both the organic and the inorganic pollutants was assumed. Zn inhibited the activity of laccase-like oxidase, whereas oil sludge promoted laccase and ascorbate oxidase activities. This finding suggests that these enzymes play a part in the oxidative detoxification of the organic pollutаnt. With both pollutants used jointly, Zn accumulation in the roots increased 6-fold, leading to increase in the efficiency of soil clean-up from the metal. In turn, Zn did not significantly affect the soil clean-up from oil sludge. This study shows for the first time the effect of co-contamination of soil with oil sludge and Zn on the physiological and biochemical characteristics of the bioenergetic plant M. × giganteus. The data obtained are important for understanding the mechanisms of phytoremediation with this plant.

Combined effects of cadmium and oil sludge on sorghum: growth, physiology, and contaminant removal.

The physiological and biochemical responses of Sorghum bicolor (L.) Moench. to cadmium (Cd) (30 mg kg-1) and oil sludge (OS) (16 g kg-1) present in soil both separately and as a mixture were studied in pot experiments. The addition of oil sludge as a co-contaminant decreased Cd entry into the plant by almost 80% and simultaneously decreased the stimulation of superoxide dismutase (SOD) and peroxidase. The decrease in glutathione reductase (GR) activity and the increase in glutathione-S-transferase (GST) activity under the influence of oil sludge indicated that its components were detoxified by conjugation with glutathione. Cd additionally activated the antioxidant and detoxifying potential of the plant enzymatic response to stress. This helped to enhance the degradation rate of oil sludge in the rhizosphere, in which the participation of the root-released enzymes in the degradation could be possible. Cd increased the extent of soil clean-up from oil sludge, mainly owing to the elimination of paraffins, naphthenes, and mono- and bicyclic aromatic hydrocarbons. The mutual influence of the pollutants on the biochemical responses of sorghum and on soil clean-up was evaluated. The results are important for understanding the antistress and detoxification responses of the remediating plant to combined environmental pollution.

Bioremediation potential of a halophilic Halobacillus sp. strain, EG1HP4QL: exopolysaccharide production, crude oil degradation, and heavy metal tolerance.

A halophilic bacterial strain, EG1HP4QL, was isolated from a salt sample from Lake Qarun, Fayoum Province, Egypt. Morphological, physiological, biochemical, and phylogenetic analyses indicated that the strain belonged to the genus Halobacillus. Strain EG1HP4QL produced an extracellular polysaccharide (EPS), with production peaking (5.9 g L-1) during growth on medium S-G containing 2% (w/v) sucrose at 35 °C (pH 8.0). The EPS had significant emulsifying activity (E24 %) against kerosene (65.7 ± 0.8%), o-xylene (64.0 ± 1%), and sunflower oil (44.7 ± 0.5%). The composition of the EPS included two polymers-a negatively charged and a neutral one (~ 3:1)-in which mannose and glucose were the main neutral monosaccharide constituents. Strain EG1HP4QL was able to utilize crude oil (35.3%) as the sole carbon source within 12 days. The minimum inhibitory concentrations of heavy metals [Zn(II), Cd(II), Pb(II), Ni(II), and Cu(II)] for strain EG1HP4QL were 1.0, 2.0, 2.0, 2.5, and 5 mM, respectively.

Comparison of the phytoremediation potentials of Medicago falcata L. And Medicago sativa L. in aged oil-sludge-contaminated soil.

Thirteen-year monitoring of the vegetation growing in the industrial and adjacent areas of an oil refinery showed the prevalence of yellow medick (Medicago falcata L.) over other plant species, including alfalfa (Medicago sativa L.). A comparative field study of the two Medicago species established that yellow medick and alfalfa exhibited similar resistance to soil petroleum hydrocarbons and that the pollutant concentration in their rhizosphere was 30% lower than that in the surrounding bulk soil. In laboratory pot experiments, yellow medick reduced the contaminant content by 18% owing to the degradation of the major heavy oil fractions, such as paraffins, naphthenes, and alcohol and benzene tars; and it was more successful than alfalfa. Both species were equally effective in stimulating the total number of soil microorganisms, but the number of hydrocarbon-oxidizing microorganisms, including polycyclic aromatic hydrocarbon degraders, was larger in the root zone of alfalfa. In turn, yellow medick provided a favorable balance of available nitrogen. Both Medicago species equally stimulated the dehydrogenase and peroxidase activities of the soil, and yellow medick increased the activity of soil polyphenol oxidase but reduced the activity of catalase. The root tissue activity of catalase, ascorbate oxidase, and tyrosinase was grater in alfalfa than in yellow medick. The peroxidase activity of plant roots was similar in both species, but nondenaturing polyacrylamide gel electrophoresis showed some differences in the peroxidase profiles of the root extracts of alfalfa and yellow medick. Overall, this study suggests that the phytoremediation potentials of yellow medick and alfalfa are similar, with some differences.

Effect of cadmium stress and inoculation with a heavy-metal-resistant bacterium on the growth and enzyme activity of Sorghum bicolor.

In this study, the influence of the heavy-metal-resistant rhizobacterial inoculant Rhodococcus ruber N7 on the growth and enzyme activity of Sorghum bicolor (L.) Moench. under cadmium stress was investigated in quartz sand pot experiments. The effect of cadmium and bacterium on the plant biomass accumulation, photosynthetic pigments, protein content, and the activities of plant-tissue enzymes such as peroxidase, laccase, and tyrosinase were estimated. It was shown that the presence of cadmium in the sand influenced the roots to a greater extent than it influenced the aerial parts of sorghum. This is manifested as increased protein content, reduced activity of peroxidase, and increased activity of laccase. Compared with cadmium stress, inoculation of plants with rhizobacterium R. ruber N7 has a stronger (and often opposite) effect on the biochemical parameters of sorghum, including a decrease in the concentration of protein in the plant, but increased the activity of peroxidase, laccase, and tyrosinase. Under cadmium contamination of sand, R. ruber N7 successfully colonizes the roots of Sorghum bicolor, survives in its root zone, and contributes to the accumulation of the metal in the plant roots, thereby reducing the concentration of the pollutant in the environment.