Biodegradation of binary mixtures of octane with benzene, toluene, ethylbenzene or xylene (BTEX): insights on the potential of Burkholderia, Pseudomonas and Cupriavidus isolates

Risk assessment of Benzene, Toluene, Ethyl benzene, and Xylene (BTEX) in the atmospheric air around the world: A review

Volatile organic compounds, such as BTEX, have been the subject of numerous debates due to their detrimental effects on the environment and human health. Human beings have had a significant role in the emergence of this situation. Even though US EPA, WHO, and other health-related organizations have set standard limits as unhazardous levels, it has been observed that within or even below these limits, constant exposure to these toxic chemicals results in negative consequences as well. According to these facts, various studies have been carried out all over the world - 160 of which are collected within this review article, so that experts and governors may come up with effective solutions to manage and control these toxic chemicals. The outcome of this study will serve the society to evaluate and handle the risks of being exposed to BTEX. In this review article, the attempt was to collect the most accessible studies relevant to risk assessment of BTEX in the atmosphere, and for the article to contain least bias, it was reviewed and re-evaluated by all authors, who are from different institutions and backgrounds, so that the insights of the article remain unbiased. There may be some limitations to consistency or precision in some points due to the original sources, however the attempt was to minimize them as much as possible.

Broad-spectrum hydrocarbon-degrading microbes in the global ocean metagenomes

Understanding the diversity and functions of hydrocarbon-degrading microorganisms in marine environments is crucial for both advancing knowledge of biogeochemical processes and improving bioremediation methods. In this study, we leveraged nearly 20,000 metagenome-assembled genomes (MAGs), recovered from a wide array of marine samples across the global oceans, to map the diversity of aerobic hydrocarbon-degrading microorganisms. A broad bacterial diversity was uncovered, with a notable preference for degrading aliphatic hydrocarbons over aromatic ones, primarily within Proteobacteria and Actinobacteriota. Three types of broad-spectrum hydrocarbon-degrading bacteria were identified for their ability to degrade various hydrocarbons and possession of multiple copies of hydrocarbon biodegradation genes. These bacteria demonstrate extensive metabolic versatility, aiding their survival and adaptability in diverse environmental conditions. Evidence of gene duplication and horizontal gene transfer in these microbes suggested a potential enhancement in the diversity of hydrocarbon-degrading bacteria. Positive correlations were observed between the abundances of hydrocarbon-degrading genes and environmental parameters such as temperature (-5 to 35 °C) and salinity (20 to 42 PSU). Overall, our findings offer valuable insights into marine hydrocarbon-degrading microorganisms and suggest considerations for selecting microbial strains for oil pollution remediation.

Effects of municipal waste compost on microbial biodiversity and energy production in terrestrial microbial fuel cells

Microbial Fuel Cells (MFCs) transform organic matter into electricity through microbial electrochemical reactions catalysed on anodic and cathodic half-cells. Terrestrial MFCs (TMFCs) are a bioelectrochemical system for bioelectricity production as well as soil remediation. In TMFCs, the soil is the ion-exchange electrolyte, whereas a biofilm on the anode oxidises organic matter through electroactive bacteria. Little is known of the overall microbial community composition in a TMFC, which impedes complete exploitation of the potential to generate energy in different soil types. In this context, an experiment was performed to reveal the prokaryotic community structure in single chamber TMFCs with soil in the presence and absence of a municipal waste compost (3% w/v). The microbial community was assessed on the anode and cathode and in bulk soil at the end of the experiment (54 days). Moreover, TMFC electrical performance (voltage and power) was also evaluated over the experimental period, varying the external resistance to improve performance. Compost stimulated soil microbial activity, in line with a general increase in voltage and power. Significant differences were observed in the microbial communities between initial soil conditions and TMFCs, and between the anode, cathode and bulk soil in the presence of the compost. Several electroactive genera (Bacillus, Fulvivirga, Burkholdeira and Geobacter) were found at the anode in the presence of compost. Overall, the use of municipal waste compost significantly increased the performance of the MFCs in terms of electrical power and voltage generated, not least thanks to the selective pressure towards electroactive bacteria on the anode.

Current trends in bioremediation and bio-integrated treatment of petroleum hydrocarbons

Petroleum hydrocarbons and their derivatives constitute the leading group of environmental pollutants worldwide. In the present global scenario, petroleum and natural gas production, exploration, petroleum refining, and other anthropogenic activities produce huge amounts of hazardous petroleum wastes that accumulate in the terrestrial and marine environment. Due to their carcinogenic, neurotoxic, and mutagenic characteristics, petroleum pollutants pose severe risks to human health and exert ecotoxicological effects on the ecosystems. To mitigate petroleum hydrocarbons (PHs) contamination, implementing "green technologies" for effective cleanup and restoration of an affected environment is considered as a pragmatic approach. This review provides a comprehensive outline of newly emerging bioremediation technologies, for instance; nanobioremediation, electrokinetic bioremediation, vermiremediation, multifunctional and sustainably implemented on-site applied biotechnologies such as; natural attenuation, biostimulation, bioaugmentation, bioventing, phytoremediation and multi-process hybrid technologies. Additionally, the scope of the effectiveness and limitations of individual technologies in treating the petroleum hydrocarbon polluted sites are also evaluated.

Metagenomic analysis reveals specific BTEX degrading microorganisms of a bacterial consortium

Petroleum hydrocarbon contamination is of environmental and public health concerns due to its toxic components. Bioremediation utilizes microbial organisms to metabolism and remove these contaminants. The aim of this study was to enrich a microbial community and examine its potential to degrade petroleum hydrocarbon. Through successive enrichment, we obtained a bacterial consortium using crude oil as sole carbon source. The 16 S rRNA gene analysis illustrated the structural characteristics of this community. Metagenomic analysis revealed the specific microbial organisms involved in the degradation of cyclohexane and all the six BTEX components, with a demonstration of the versatile metabolic pathways involved in these reactions. Results showed that our consortium contained the full range of CDSs that could potentially degrade cyclohexane, benzene, toluene, and (o-, m-, p-) xylene completely. Interestingly, a single taxon that possessed all the genes involved in either the activation or the central intermediates degrading pathway was not detected, except for the Novosphingobium which contained all the genes involved in the upper degradation pathway of benzene, indicating the synergistic interactions between different bacterial genera during the hydrocarbon degradation.

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.

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) by microbial consortium from paddy rice soil

Polycyclic aromatic hydrocarbons (PAHs) are among the most widely spread pollutants in the environment including the agricultural soil. PAH degradation by indigenous bacteria is an effective and economical means to remove these pollutants from the environment. Here, we report a bacterial consortium (Pdy-1) isolated from paddy rice soil in northern Japan able to degrade polycyclic aromatic hydrocarbons (PAHs) at high rates. Pdy-1 was incubated with a mixture of PAH compounds (fluorene, phenanthrene, and pyrene) in Bushnell Haas Medium at a final concentration of 100 mg/L each. PDY-1 degraded 100% of fluorene, 95% of phenanthrene, and 52% of pyrene in 5 days. Phenanthrene and pyrene were completely degraded at 10 d and 15 d, respectively. Cloning of the 16S rRNA gene revealed that the consortium was composed of 40% Achromobacter and 7% each of Castelaniella, Rhodanobacter, and Hypomicrobium. Comamonas, Ferrovibrio, Terrimonas, Bordetella, Rhizobium, and Pseudonocardia were also detected. PCR-DGGE showed the dynamics of the consortium during the incubation period. Real-time PCR revealed that PAH degrading genes such as the gram-positive ring dihydroxylating genes (PAH-RDH) and pyrene dioxygenase (nidA) were most abundant at day 5 when the rapid biodegradation of the PAHs was observed. This study improves our understanding on dynamics and characteristics of an effective PAH-degrading bacterial consortium from paddy rice soil.

Nature-Based Solutions for Restoring an Agricultural Area Contaminated by an Oil Spill

A feasibility study is presented for a bioremediation intervention to restore agricultural activity in a field hit by a diesel oil spill from an oil pipeline. The analysis of the real contaminated soil was conducted following two approaches. The first concerned the assessment of the biodegradative capacity of the indigenous microbial community through laboratory-scale experimentation with different treatments (natural attenuation, landfarming, landfarming + bioaugmentation). The second consisted of testing the effectiveness of phytoremediation with three plant species: Zea mays (corn), Lupinus albus (lupine) and Medicago sativa (alfalfa). With the first approach, after 180 days, the different treatments led to biodegradation percentages between 83 and 96% for linear hydrocarbons and between 76 and 83% for branched ones. In case of contamination by petroleum products, the main action of plants is to favor the degradation of hydrocarbons in the soil by stimulating microbial activity thanks to root exudates. The results obtained in this experiment confirm that the presence of plants favors a decrease in the hydrocarbon content, resulting in an improved degradation of up to 18% compared with non-vegetated soils. The addition of plant growth-promoting bacteria (PGPB) isolated from the contaminated soil also promoted the growth of the tested plants. In particular, an increase in biomass of over 50% was found for lupine. Finally, the metagenomic analysis of the contaminated soil allowed for evaluating the evolution of the composition of the microbial communities during the experimentation, with a focus on hydrocarbon- oxidizing bacteria.

Current research on simultaneous oxidation of aliphatic and aromatic hydrocarbons by bacteria of genus Pseudomonas

One of the most frequently used methods for elimination of oil pollution is the use of biological preparations based on oil-degrading microorganisms. Such microorganisms often relate to bacteria of the genus Pseudomonas. Pseudomonads are ubiquitous microorganisms that often have the ability to oxidize various pollutants, including oil hydrocarbons. To date, individual biochemical pathways of hydrocarbon degradation and the organization of the corresponding genes have been studied in detail. Almost all studies of this kind have been performed on degraders of individual hydrocarbons belonging to a single particular class. Microorganisms capable of simultaneous degradation of aliphatic and aromatic hydrocarbons are very poorly studied. Most of the works on such objects have been devoted only to phenotype characteristic and some to genetic studies. To identify the patterns of interaction of several metabolic systems depending on the growth conditions, the most promising are such approaches as transcriptomics and proteomics, which make it possible to obtain a comprehensive assessment of changes in the expression of hundreds of genes and proteins at the same time. This review summarizes the existing data on bacteria of the genus Pseudomonas capable of the simultaneous oxidation of hydrocarbons of different classes (alkanes, monoaromatics, and polyaromatics) and presents the most important results obtained in the studies on the biodegradation of hydrocarbons by representatives of this genus using methods of transcriptomic and proteomic analyses.

From Surface Water to the Deep Sea: A Review on Factors Affecting the Biodegradation of Spilled Oil in Marine Environment

Over the past century, the demand for petroleum products has increased rapidly, leading to higher oil extraction, processing and transportation, which result in numerous oil spills in coastal-marine environments. As the spilled oil can negatively affect the coastal-marine ecosystems, its transport and fates captured a significant interest of the scientific community and regulatory agencies. Typically, the environment has natural mechanisms (e.g., photooxidation, biodegradation, evaporation) to weather/degrade and remove the spilled oil from the environment. Among various oil weathering mechanisms, biodegradation by naturally occurring bacterial populations removes a majority of spilled oil, thus the focus on bioremediation has increased significantly. Helping in the marginal recognition of this promising technique for oil-spill degradation, this paper reviews recently published articles that will help broaden the understanding of the factors affecting biodegradation of spilled oil in coastal-marine environments. The goal of this review is to examine the effects of various environmental variables that contribute to oil degradation in the coastal-marine environments, as well as the factors that influence these processes. Physico-chemical parameters such as temperature, oxygen level, pressure, shoreline energy, salinity, and pH are taken into account. In general, increase in temperature, exposure to sunlight (photooxidation), dissolved oxygen (DO), nutrients (nitrogen, phosphorous and potassium), shoreline energy (physical advection—waves) and diverse hydrocarbon-degrading microorganisms consortium were found to increase spilled oil degradation in marine environments. In contrast, higher initial oil concentration and seawater pressure can lower oil degradation rates. There is limited information on the influences of seawater pH and salinity on oil degradation, thus warranting additional research. This comprehensive review can be used as a guide for bioremediation modeling and mitigating future oil spill pollution in the marine environment by utilizing the bacteria adapted to certain conditions.