Prospects in the bioremediation of petroleum hydrocarbon contaminants from hypersaline environments: A review

Functional and structural responses of a halophilic consortium to oily sludge during biodegradation

Biotreatment of oily sludge and the involved microbial communities, particularly in saline environments, have been rarely investigated. We enriched a halophilic bacterial consortium (OS-100) from petroleum refining oily sludge, which degraded almost 86% of the aliphatic hydrocarbon (C10-C30) fraction of the oily sludge within 7 days in the presence of 100 g/L NaCl. Two halophilic hydrocarbon-degrading bacteria related to the genera Chromohalobacter and Halomonas were isolated from the OS-100 consortium. Hydrocarbon degradation by the OS-100 consortium was relatively higher compared to the isolated bacteria, indicating potential synergistic interactions among the OS-100 community members. Exclusion of FeCl2, MgCl2, CaCl2, trace elements, and vitamins from the culture medium did not significantly affect the hydrocarbon degradation efficiency of the OS-100 consortium. To the contrary, hydrocarbon biodegradation dropped from 94.1 to 54.4% and 5% when the OS-100 consortium was deprived from phosphate and nitrogen sources in the culture medium, respectively. Quantitative PCR revealed that alkB gene expression increased up to the 3rd day of incubation with 11.277-fold, consistent with the observed increments in hydrocarbon degradation. Illumina-MiSeq sequencing of 16 S rRNA gene fragments revealed that the OS-100 consortium was mainly composed of the genera Halomonas, Idiomarina, Alcanivorax and Chromohalobacter. This community structure changed depending on the culturing conditions. However, remarkable changes in the community structure were not always associated with remarkable shifts in the hydrocarbonoclastic activity and vice versa. The results show that probably synergistic interactions between community members and different subpopulations of the OS-100 consortium contributed to salinity tolerance and hydrocarbon degradation.

Review of carbon dot-hydrogel composite material as a future water-environmental regulator

As water pollution and scarcity pose severe threats to the sustainable progress of human society, it is important to develop a method or materials that can accurately and efficiently detect pollutants and purify aquatic environments or exploit marine resources. The compositing of photoluminescent and hydrophilic carbon dots (CDs) with hydrogels bearing three-dimensional networks to form CD-hydrogel composites to protect aquatic environments is a "win-win" strategy. Herein, the feasibility of the aforementioned method has been demonstrated. This paper reviews the recent progress of CD-hydrogel materials used in aquatic environments. First, the synthesis methods for these composites are discussed, and then, the composites are categorized according to different methods of combining the raw materials. Thereafter, the progress in research on CD-hydrogel materials in the field of water quality detection and purification is reviewed in terms of the application of the mechanisms. Finally, the current challenges and prospects of CD-hydrogel materials are described. These results are expected to provide insights into the development of CD-hydrogel composites for researchers in this field.

Biochar-bacteria-plant combined potential for remediation of oil-contaminated soil

Oil pollution is a common type of soil organic pollution that is harmful to the ecosystem. Bioremediation, particularly microbe-assisted phytoremediation of oil-contaminated soil, has become a research hotspot in recent years. In order to explore more appropriate bioremediation strategies for soil oil contamination and the mechanism of remediation, we compared the remediation effects of three plants when applied in combination with a microbial agent and biochar. The combined remediation approach of Tagetes erecta, microbial agent, and biochar exhibited the best plant growth and the highest total petroleum hydrocarbons degradation efficiency (76.60%). In addition, all of the remediation methods provided varying degrees of restoration of carbon and nitrogen contents of soils. High-throughput sequencing found that microbial community diversity and richness were enhanced in most restored soils. Some soil microorganisms associated with oil degradation and plant growth promotion such as Cavicella, C1_B045, Sphingomonas, MND1, Bacillus and Ramlibacter were identified in this study, among which Bacillus was the major component in the microbial agent. Bacillus was positively correlated with all soil remediation indicators tested and was substantially enriched in the rhizosphere of T. erecta. Functional gene prediction of the soil bacterial community based on the KEGG database revealed that pathways of carbohydrate metabolism and amino acid metabolism were up-regulated during remediation of oil-contaminated soils. This study provides a potential method for efficient remediation of oil-contaminated soils and thoroughly examines the biochar-bacteria-plant combined remediation mechanisms of oil-contaminated soil, as well as the combined effects from the perspective of soil bacterial communities.

Microbial Remediation of Crude Oil in Saline Conditions by Oil-Degrading Bacterium Priestia megaterium FDU301

Salinity greatly affects the microbial degradation process of crude oil; thus, the isolation and identification of halotolerant microbes is essential. Limited studies explored how microbes respond to increased salinity. In this study, an oil-degrading bacterium Priestia megaterium FDU301 was isolated from the Dagang oil field, which can tolerate a salinity of 6%. Compared to the non-saline condition, oil degradation ratios by P. megaterium FDU301 increased by 15.27% and 11.26% in 0.5% and 3.5% salinity media, respectively. Meanwhile, bacteria degraded various components of crude oil more thoroughly in saline environments, especially mid-chain hydrocarbons (C11-C18). Surface tension under salt stress was lower than that in the non-saline medium, indicating that the amount of biosurfactants produced by bacteria was increased. The microbial activity enhanced markedly in response to increased salinity, which was the main factor for the high degradation ability. As a vital component of biofilms, the production of polysaccharides was accelerated with P. megaterium FDU301 inoculation in saline environments. These results indicate that P. megaterium FDU301 has great potential application in oil bioremediation in saline environments.

Mitigation of hydrocarbon toxicity using bacterial consortium in microcosm environment for agrarian fecundity

Petroleum contamination in the soil has been well emphasized as a toxic and hazardous soil pollution contributing to a significant portion of soil infertility worldwide. In the present study, bacterial consortium CHM1 composed of 5 strains belonging to genera Klebsiella, Pantoea, and Enterobacter was evaluated for hydrocarbon degradation ability in the soil environment, as well as their performance in remediating ecotoxicity and phytotoxicity. Initially, the degradation efficiency (1.98%/day) in the soil environment was evaluated. Scanning Electron Microscopy combined with Energy Dispersive X-ray spectroscopy revealed an increase in nitrogen content by 24.98% and a decrease in carbon content by 22.76% implying an improvement in soil fertility. The Fourier Transform InfraRed spectroscopy and Gas Chromatographic analysis revealed significant depletion of aromatic, cyclic, long aliphatic, and complex acid and ester content of the test soil. Moreover, the quantitative PCR analysis exhibited the non-competitive coexistence of each component of the CHM1 consortium. Different enzymatic assays revealed elevated dehydrogenase and superoxide dismutase activity in the degradation system due to the introduction of CHM1 in the soil microcosm. Vibrio fischeri-assisted ecotoxicity analysis had established the potential of CHM1 to efficiently minimize the ecotoxicity of hydrocarbon contamination. The phytotoxicity analysis was performed using four different plant models viz. Chickpeas (Cicer arientinum), Coriander (Coriandrum sativum), Fenugreek (Trigonella foenum-graecum), and Spinach (Spinacia oleracea) exhibiting CHM1 amendment helped to restore plant germination and growth in hydrocarbon-contaminated soil system efficiently. The promising results from this study indicated the possible application of the bacterial consortium in hydrocarbon-contaminated land management and soil restoration for cultivation or other plantation purposes.

Enhanced degradation of petroleum in saline soil by nitrogen stimulation and halophilic emulsifying bacteria Bacillus sp. Z-13

Remediation of petroleum-contaminated soil is a widely concerned challenge. As an ecofriendly method, the performance improvement of indigenous microbial degradation is facing the bottleneck. In this study, a strain with high efficiency of petroleum degradation was isolated from the petroleum-contaminated soil and identified and named as Bacillus sp. Z-13. The strain showed the ability to produce lipopeptide surfactant which could improve 66% more petroleum hydrocarbons eluted. Strain Z-13 and its biosurfactant exhibited broad environmental adaptability to salinity (0-8%), pH (6-9) and temperature (15-45 °C). With the addition of strain Z-13 and the stimulation of NH4Cl, up to 59% of the petroleum in the contaminated soil was removed at the carbon to nitrogen ratio of 10. Microbial community analysis showed that petroleum-degrading bacteria, represented by Bacillus, became the dominant species at genus level and played an important role in the remediation. Additionally, ammonium stimulation facilitated both pathways of ammonium assimilation and nitrification in native microorganisms to achieve efficient degradation of petroleum hydrocarbons. This study could provide a promising approach for stable, environmental-friendly and efficient remediation of petroleum-contaminated soil.

Exploring the bioremediation capability of petroleum-contaminated soils for enhanced environmental sustainability and minimization of ecotoxicological concerns

The bioremediation of soils contaminated with petroleum hydrocarbons (PHCs) has emerged as a promising approach, with its effectiveness contingent upon various types of PHCs, i.e., crude oil, diesel, gasoline, and other petroleum products. Strategies like genetically modified microorganisms, nanotechnology, and bioaugmentation hold potential for enhancing remediation of polycyclic aromatic hydrocarbon (PAH) contamination. The effectiveness of bioremediation relies on factors such as metabolite toxicity, microbial competition, and environmental conditions. Aerobic degradation involves enzymatic oxidative reactions, while bacterial anaerobic degradation employs reductive reactions with alternative electron acceptors. Algae employ monooxygenase and dioxygenase enzymes, breaking down PAHs through biodegradation and bioaccumulation, yielding hydroxylated and dihydroxylated intermediates. Fungi contribute via mycoremediation, using co-metabolism and monooxygenase enzymes to produce CO2 and oxidized products. Ligninolytic fungi transform PAHs into water-soluble compounds, while non-ligninolytic fungi oxidize PAHs into arene oxides and phenols. Certain fungi produce biosurfactants enhancing degradation of less soluble, high molecular-weight PAHs. Successful bioremediation offers sustainable solutions to mitigate petroleum spills and environmental impacts. Monitoring and assessing strategy effectiveness are vital for optimizing biodegradation in petroleum-contaminated soils. This review presents insights and challenges in bioremediation, focusing on arable land safety and ecotoxicological concerns.

Response to Hypersalinity of Four Halophytes Growing in Hydroponic Floating Systems: Prospects in the Phytomanagement of High Saline Wastewaters and Extreme Environments

Hypersaline environments occur naturally worldwide in arid and semiarid regions or in artificial areas where the discharge of highly saline wastewaters, such as produced water (PW) from oil and gas industrial setups, has concentrated salt (NaCl). Halophytes can tolerate high NaCl concentrations by adopting ion extrusion and inclusion mechanisms at cell, tissue, and organ levels; however, there is still much that is not clear in the response of these plants to salinity and completely unknown issues in hypersaline conditions. Mechanisms of tolerance to saline and hypersaline conditions of four different halophytes (Suaeda fruticosa (L.) Forssk, Halocnemum strobilaceum (Pall.) M. Bieb., Juncus maritimus Lam. and Phragmites australis (Cav.) Trin. ex Steudel) were assessed by analysing growth, chlorophyll fluorescence and photosynthetic pigment parameters, nutrients, and sodium (Na) uptake and distribution in different organs. Plants were exposed to high saline (257 mM or 15 g L^-1 NaCl) and extremely high or hypersaline (514, 856, and 1712 mM or 30, 50, and 100 g L^-1 NaCl) salt concentrations in a hydroponic floating culture system for 28 days. The two dicotyledonous S. fruticosa and H. strobilaceum resulted in greater tolerance to hypersaline concentrations than the two monocotyledonous species J. maritimus and P. australis. Plant biomass and major cation (K, Ca, and Mg) distributions among above- and below-ground organs evidenced the osmoprotectant roles of K in the leaves of S. fruticosa, and of Ca and Mg in the leaves and stem of H. strobilaceum. In J. maritimus and P. australis the rhizome modulated the reduced uptake and translocation of nutrients and Na to shoot with increasing salinity levels. S. fruticosa and H. strobilaceum absorbed and accumulated elevated Na amounts in the aerial parts at all the NaCl doses tested, with high bioaccumulation (from 0.5 to 8.3) and translocation (1.7-16.2) factors. In the two monocotyledons, Na increased in the root and rhizome with the increasing concentration of external NaCl, dramatically reducing the growth in J. maritimus at both 50 and 100 g L^-1 NaCl and compromising the survival of P. australis at 30 g L^-1 NaCl and over after two weeks of treatment.

Soil treatment using a biosurfactant producing bacterial consortium in rice fields contaminated with oily sludge- a sustainable approach

A consortium of two biosurfactant-producing bacteria (Bacillus pumilus KS2 and Bacillus cereus R2) was developed to remediate petroleum hydrocarbon-contaminated paddy soil. Soil samples from a heavily contaminated rice field near Assam's Lakwa oilfield were collected and placed in earthen pots for treatment. After each month of incubation, 50 g of soil from each earthen pot was collected, and the soil TPH (ppm) in each sample was determined. The extracted TPH samples were analysed by Gas chromatography-mass spectrometry (GC-MS) to confirm microbial degradation. The soil samples were examined for changes in pH, conductivity, total organic content (TOC), water holding capacity, and total nitrogen content in addition to TPH degradation. An increasing trend in TPH degradation was observed with each passing month. After six months of treatment, the sample with the lowest initial TPH concentration (1735 ppm) had the highest degradation (91.24%), while the soil with the highest amount of TPH (5780 ppm) had the lowest degradation (74.35%). A wide range of aliphatic hydrocarbons found in soil samples was degraded by the bacterial consortium. The soil samples contained eight different low- and high-molecular-weight PAHs. Some were fully mineralized, while others were significantly reduced. With the decrease in the TPH level in the polluted soil, a significant improvement in the soil's physicochemical qualities (such as pH, electrical conductivity, total organic content, and water-holding capacity) was observed.