Screening the toxicity and biodegradability of petroleum hydrocarbons by a rapid colorimetric method

Ribosomal RNA gene operon copy number, a functional trait indicating the hydrocarbon degradation level of bacterial communities

The lack of universal indicators for predicting microbial biodegradation potential and assessing remediation effects limits the generalization of bioremediation. The community-level ribosomal RNA gene operon (rrn) copy number, an important functional trait, has the potential to serve as a key indicator of the bioremediation of organic pollutants. A meta-analysis based on 1275 samples from 26 hydrocarbon-related studies revealed a positive relationship between the microbial hydrocarbon biodegradation level and the community-level rrn copy number in soil, seawater and culture. Subsequently, a microcosm experiment was performed to decipher the community-level rrn copy number response mechanism during total petroleum hydrocarbon (TPH) biodegradation. The treatment combining straw with resuscitation-promoting factor (Rpf) exhibited the highest community-level rrn copy number and the most effective biodegradation compared with other treatments, and the initial TPH content (20,000 mg kg-1) was reduced by 67.67% after 77 days of incubation. TPH biodegradation rate was positively correlated with the average community-level rrn copy number (p = 0.001, R2 = 0.5781). Both meta and community analyses showed that rrn copy number may reflect the potential of hydrocarbon degradation and microbial dormancy. Our findings provide insight into the applicability of the community-level rrn copy number to assess bacterial biodegradation for pollution remediation.

Isolation of a polyethylene-degrading bacterium, Acinetobacter guillouiae, using a novel screening method based on a redox indicator

Plastic, a polymer synthesized from petrochemicals, is used worldwide. However, natural degradation of plastic is difficult, causing environmental pollution, with microplastics posing a serious threat to human health. In this study, we aimed to use a new screening method based on the oxidation-reduction indicator, 2,6-dichlorophenolindophenol, to isolate a polyethylene-degrading bacterium, Acinetobacter guillouiae, from insect larvae. Plastic-degrading strains are identified by the color change in the redox indicator from blue to colorless as plastic metabolism occurs. Polyethylene biodegradation by A. guillouiae was verified through weight loss, surface erosion, physiological evidence, and chemical changes on the plastic surface. In addition, we analyzed the characteristics of hydrocarbon metabolism in polyethylene-degrading bacteria. Results suggested that alkane hydroxylation and alcohol dehydrogenation were key steps in polyethylene degradation. This novel screening method will pave the way for high-throughput screening of polyethylene-degrading microorganisms and extending its application to other types of plastics may potentially address plastic pollution.

Evaluation of Bacillus subtilis as a Tool for Biodegrading Diesel Oil and Gasoline in Experimentally Contaminated Water and Soil

Benzene, toluene, ethylbenzene and xylene (BTEX) are toxic petroleum hydrocarbons pollutants that can affect the central nervous system and even cause cancer. For that reason, studies regarding BTEX degradation are extremely important. Our study aimed evaluate the microorganism Bacillus subtilis as a tool for degrading petroleum hydrocarbons pollutants. Assays were run utilizing water or soil distinctly contaminated with gasoline and diesel oil, with and without B. subtilis. The ability of B. subtilis to degrade hydrophobic compounds was analyzed by Fourier-Transform Infrared Spectroscopy (FTIR) and gas chromatography. The FTIR results indicated, for water assays, that B. subtilis utilized the gasoline and diesel oil to produce the biosurfactant, and, as a consequence, performed a biodegradation process. In the same way, for soil assay, B. subtilis biodegraded the diesel oil. The gas chromatography results indicated, for gasoline in soil assay, the B. subtilis removed BTEX. So, B. subtilis was capable of degrading BTEX, producing biosurfactant and it can also be used for other industrial applications. Bioremediation can be an efficient, economical, and versatile alternative for BTEX contamination.

Level of oxidative stress for the land snail Cepaea nemoralis from aged and bioremediated soil contaminated with petroleum products

Here, we investigated whether the widely distributed snail Cepaea nemoralis could be used as a suitable sentinel animal for assessing the effects of soil contaminants-petroleum oil derivatives-after years of soil ageing and treatment with a bacterial formulation. Oxidative stress was assessed in the foot and hepatopancreas of C. nemoralis L. exposed to soil contaminated with unleaded petrol, spent engine oil or diesel oil and bioremediated with a bacterial formulation (soil was used 2 years after contamination and bioremediation process). We measured total antioxidant capacity, catalase and glutathione transferase activity and concentrations of superoxide anions, hydrogen peroxide and protein carbonyls in the foot and hepatopancreas of snails after 2 and 4 weeks of treatment. The studied antioxidant responses appeared largely to be tissue and remediation process specific, while the concentrations of superoxide anions, hydrogen peroxide and protein carbonyls depended on time of exposure, tissue type and the type of contaminants, but mostly not on the remediation process. Generally, changes in the concentrations of superoxide anions, hydrogen peroxide and protein carbonyls in the hepatopancreas of snails seemed to be a suitable measure to assess the risk of animals exposed to soil contaminated with petroleum substances and used after many years of ageing and treatment with a microbial formulation.

Bioelectrochemical degradation of petroleum hydrocarbons: A critical review and future perspectives

As typical pollutants, petroleum hydrocarbons that are widely present in various environmental media such as soil, water, sediments, and air, seriously endanger living organisms and human health. In the meantime, as a green environmental technology that integrates pollutant removal and resource recovery, bioelectrochemical systems (BESs) have been extensively applied to the removal of petroleum hydrocarbons from the environment. This review introduces working principles of BESs, following which it discusses the different reactor structures, application progresses, and key optimization factors when treating water, sewage sludges, sediments, and soil. Furthermore, bibliometrics was first used in this field to analyze the evolution of knowledge structure and forecast future hot topics. The research focus has shifted from the early generation of bioelectric energy to exploring mechanisms of soil remediation and microbial metabolisms, which will be closely integrated in the future. Finally, the future prospects of this field are proposed. This review focuses on the research status of bioelectrochemical degradation of petroleum hydrocarbons and provides a scientific reference for subsequent research.

Fast biodegradation of long-alkanes by enhancing bacteria performance rate by per-oxidation

The long-alkanes biodegradation rate was generally found slow during widely used pre-oxidation combined with biodegradation for oil contamination treatment, resulting in long and unsustainable removal. In this study, different chitosan content was used to produce iron catalysts for pre-oxidation, and nutrients were added for the long-alkanes biodegradation experiment. Mechanism of Fenton pre-oxidation and improvement in the biodegradation rate of long-alkanes were studied by analyzing the change in organic matter and bacterial community structure, the amount and activity of bacteria in the biological stage, and the degradation amount long-alkanes hydrocarbon before and after pre-oxidation. Results showed that the destruction of bacteria greatly reduced when hydroxyl radical intensity decreased to 4.40 a.u.. Also, the proportion of humic acid-like was high (40.88%), and the community structure was slightly changed with the pre-oxidation for the fast biodegradation (FB) group. In the subsequent biodegradation, it was found that the degradation rate of each long-alkanes in the FB group increased significantly (C₃₀: 4.18-8.32 mg/(kg·d)) with the increase of the degradation of long-alkanes (10-50%). Further studies showed that the high nutrient dynamics (6.05 mg/(kg·d)) of the FB group resulted in high bacteria performance rate (0.53 mol CO₂ × log CFU/(10⁴ g² d)), which further accelerated the substrate transformation(41%). Therefore, the biodegradation rate of long-alkanes was increased (43.8 mg/(kg·d)) with the removal rate of long-alkanes of 76%. The half-life of long-alkanes for the FB group (64 d) was 33 d shorter than the slow biodegradation group (99 d). These results exhibited that pre-oxidation regulation can shorten the bioremediation cycle by improving the biodegradation rate of long-alkanes. This research has good engineering application value.

Exploitation of extracellular organic matter from Micrococcus luteus to enhance ex situ bioremediation of soils polluted with used lubricants

Chronic pollution by used lubricant oils (ULOs) poses a serious challenge to the environment. Under stress conditions, microorganisms, including potential degraders, can enter a viable but non-culturable (VBNC) state, complicating the bioremediation of ULO-polluted areas. Resuscitation-promoting factors (Rpfs) can reverse this transition and/or enhance the biodegradation performance of both native and augmented strains. Here, Rpf-containing extracellular organic matter (EOM) from Micrococcus luteus was used to enhance the ex situ ULO removal in biostimulated and bioaugmented (with Rhodococcus qingshengii KAG C, R. erythropolis PR4) soils. ULO bioconversion, microbial activity, and CFUs were significantly higher in EOM-treated soils compared to corresponding control soils. After 60 days, the initial ULO concentration (52,500 mg kg^-1) was reduced by 37% and 45% with EOM-supplemented biostimulation and bioaugmentation, respectively. Based on high-throughput 16S rRNA analysis, the enhancement was attributable both to the reactivation of EOM-responsive hydrocarbonoclastic bacterial genera (e.g., Pseudomonas, Comamonas, Stenotrophomonas, Gordonia) and to the long-term positive effect of EOM on the degradative efficacy of the introduced rhodococci. Ecotoxicological responses revealed that reduced ULO concentration did not correlate with decreased soil toxicity. Our findings provide an insight into the applicability of EOM in bioremediation and its effects on the soil microbial activity and community composition.

A Review and Bibliometric Analysis on Applications of Microbial Degradation of Hydrocarbon Contaminants in Arctic Marine Environment at Metagenomic and Enzymatic Levels

The globe is presently reliant on natural resources, fossil fuels, and crude oil to support the world's energy requirements. Human exploration for oil resources is always associated with irreversible effects. Primary sources of hydrocarbon pollution are instigated through oil exploration, extraction, and transportation in the Arctic region. To address the state of pollution, it is necessary to understand the mechanisms and processes of the bioremediation of hydrocarbons. The application of various microbial communities originated from the Arctic can provide a better interpretation on the mechanisms of specific microbes in the biodegradation process. The composition of oil and consequences of hydrocarbon pollutants to the various marine environments are also discussed in this paper. An overview of emerging trends on literature or research publications published in the last decade was compiled via bibliometric analysis in relation to the topic of interest, which is the microbial community present in the Arctic and Antarctic marine environments. This review also presents the hydrocarbon-degrading microbial community present in the Arctic, biodegradation metabolic pathways (enzymatic level), and capacity of microbial degradation from the perspective of metagenomics. The limitations are stated and recommendations are proposed for future research prospects on biodegradation of oil contaminants by microbial community at the low temperature regions of the Arctic.

Uptake and detoxification of diesel oil by a tropical soil Actinomycete Gordonia amicalis HS-11: Cellular responses and degradation perspectives

A tropical soil Actinomycete, Gordonia amicalis HS-11, has been previously demonstrated to degrade unsaturated and saturated hydrocarbons (squalene and n-hexadecane, respectively) in an effective manner. In present study, G. amicalis HS-11 degraded 92.85 ± 3.42% of the provided diesel oil [1% (v/v)] after 16 days of aerobic incubation. The effect of different culture conditions such as carbon source, nitrogen source, pH, temperature, and aeration on degradation was studied. During degradation, this Actinomycete synthesized surface active compounds (SACs) in an extracellular manner that brought about a reduction in surface tension from 69 ± 2.1 to 30 ± 1.1 mN m^-1 after 16 days. The morphology of cells grown on diesel was monitored by using a Field Emission Scanning Electron Microscope. Diesel-grown cells were longer and clumped with smooth surfaces, possibly due to the secretion of SACs. The interaction between the cells and diesel oil was studied by Confocal Laser Scanning Microscope. Some cells were adherent on small diesel droplets and others were present in the non-attached form thus confirming the emulsification ability of this organism. The fatty acid profiles of the organism grown on diesel oil for 48 h were different from those on Luria Bertani Broth. The genotoxicity and cytotoxicity of diesel oil before and after degradation were determined. Cytogenetic parameters such as mitotic index (MI); mitosis distribution and chromosomal aberration (type and frequency) were assessed. Oxidative stress was evaluated by measuring levels of catalase, superoxide dismutase and concentration of malondialdehyde. On the basis of these studies it was deduced that the degradation metabolites were relatively non-toxic.

Technical approaches to evaluate the surfactant-enhanced biodegradation of biodiesel and vegetable oils

This research compared the effects of biosurfactant on the biodegradation of biodiesel and vegetable oils while validating two conceptually diverging methodologies. The two experimental setups were successfully modeled towards the effects of biosurfactants during biodegradation. We established the equivalence of both methodologies from the data output. As expected, the biosurfactants caused an increased oil uptake, thus increasing biodegradation performance. Cooking oils were favored by the microbial consortium as a carbon source when compared with biodiesel fuel, especially after use in food preparation. However, we found that biodiesel substrate standout with the highest biodegradation rates. Our results might indicate that a rapid metabolic change from the original compound initially favored biodiesels during the assimilation of organic carbon for a set specialized microbial inoculum. The data output was successfully combined with mathematical models and statistical tools to describe and predict the actual environmental behavior of biodiesel and vegetable oils. The models confirmed and predicted the biodegradation effectiveness with biosurfactants and estimated the required timeframe to achieve satisfactory contaminant removal.

Rapid degradation of long-chain crude oil in soil by indigenous bacteria using fermented food waste supernatant

The objective of this study is to explore how to stimulate soil indigenous bacteria for the degradation of long-chain crude oil by adding fermented food waste supernatant (FS). Four concentrations of FS (0 mL, 0.1 mL, 1 mL, and 3 mL) were added to two oil-contaminated soils S1 and S2 for 30 days of bioremediation experiments. The results showed that the biodegradation of long-chain alkanes (C₂₉ - C₂₄) could reach up to 1756 mg/kg (49.3%, S1) and 3937 mg/kg (43.9%, S2), which were 3.1 and 3.2 times that of the non-nutrient system. In addition, the logarithmic growth rate of the indigenous hydrocarbon degraders (IHD) reached 41.5%. The long-chain crude oil can be rapidly degraded by indigenous bacteria with FS added in a short time. The glucose and acetic acid accelerated the consumption of ammonia nitrogen (NH₄⁺-N) in the prophase of bioremediation and the molar ratio of consumed carbon (contained in glucose and acetic acid) to consumed NH₄⁺-N (C/N) was high by adding FS. Thus, the IHD can multiply rapidly. The analysis of microbial diversity revealed that the IHD (genera Acinetobacter and Aquabacterium) became the dominant bacteria. Long-chain alkanes became the main carbon sources for IHD after 14 days in soil S1 and 16 days in soil S2. Thus, the rapid biodegradation of long-chain crude oil was achieved. The genus Aquabacterium which was uncultivable on crude oil medium became the dominant bacteria. This study provides an environment-friendly and sustainable remediation technology for bioremediation of oil-contaminated soils.

Metabolical shifts towards alternative BTEX biodegradation intermediates induced by perfluorinated compounds in firefighting foams

The type and concentration of perfluorinated compounds (PFCs) can induce different types of enzymes and promote alternate patterns of BTEX transformation. However, it is not known how the presence of active fluorocarbon-degrading microbial populations affects the transformation of BTEX. In addition to chemical analysis at the molecular level, our research approached the aqueous film forming fire-fighting foams (AFFF) and BTEX co-contamination at a large-scale with respirometers to quantify the total microbial metabolism of soil via CO₂ output levels. The intended outcome of this research was to obtain and characterize shifts in BTEX degradation at a set realistic environmental condition while measuring byproducts and CO₂ production. Both methodologies complimentarily provided an in-depth knowledge of the environmental behavior of fire-fighting foams. The biodegradation was monitored using headspace sampling and two types of gas chromatography: thermal conductivity detector and flame ionization detector. Headspace samples were periodically withdrawn for BTEX biodegradation and CO₂ production analysis. Our research suggests the discovery of an altered metabolic pathway in aromatic hydrocarbons biodegradation that is directly affected by fluorinated substances. The fluorinated compounds affected the BTEX biodegradation kinetics, as PFCs may contribute to a shift in styrene and catechol concentrations in co-contamination scenarios. A faster production of styrene and catechol was detected. Catechol is also rapidly consumed, thus undergoing further metabolic stages earlier under the presence of PFCs. The release of AFFF compounds not only changes byproducts output but also drastically disturbs the soil microbiota according to the highly variable CO₂ yields. Therefore, we observed a high sensitivity of microbial consortia due to PFCs in the AFFF formulation, therefore shifting their BTEX degradation routes in terms of intermediate products concentration.

The effects of fluoride based fire-fighting foams on soil microbiota activity and plant growth during natural attenuation of perfluorinated compounds

The use of fluoride based foams increases the effectiveness of fire-fighting operations, but they are also accompanied by major drawbacks regarding environmental safety of perfluorinated compounds (PFCs). The main concern with PFCs release is due to their well-known persistence and bioaccumulative potential, as they have been detected in many environmental samples. There is a significant knowledge gap on PFC toxicity to plants, even though such data could be useful towards bioremediation procedures. It is consensus that a realistic assessment of fire-fighting foam toxicity should cover as many test organisms as possible, however, few studies combine the performance of ecotoxicological tests with a detailed study of microbial communities in soil contaminated with firefighting foams. Our research evaluated the effects of natural attenuation of PFCs on the development of arugula and lettuce seeds. The effects of variable PFCs amounts were also observed in soil microbiota using the 2,6 dichlorophenol-indophenol redox dye as microbial metabolism indicator. We aimed to determine whether aqueous film forming foams toxicity increased or decreased over time in a simulated contamination scenario. We argued that the long-term biotransformation of fire-fighting foams should be taken in to account when evaluating toxicity, focusing on a time-based monitoring analysis, since potentially toxic intermediates may be formed though biodegradation. The phyto-toxicity of PFCs to lettuce and arugula was high, increasing as a function of the concentration and decreasing as a function of exposure time to the environment. However, very specific concentrations throughout biodegradation result in the formation of non-inhibiting intermediates. Therefore, variable biodegradation-dependent germination rates may be misleading on non-time-based monitoring approaches. Also, the low phyto-toxicity after 240days does not exclude the potential for PFC bioaccumulation in plants. We also proposed that the colorimetric data modelling could also establish a novel toxicity parameter to evaluate the release impacts to soil and biota. The combined assays allowed the monitoring of PFCs during long-term exposition to plants as well as their immediate effects on the same soil microbiota.