Oil uptake by plant-based sorbents and its biodegradation by their naturally associated microorganisms

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.

Oil Absorbent Polypropylene Particles Stimulate Biodegradation of Crude Oil by Microbial Consortia

Oil absorbent particles made from surface-modified polypropylene can be used to facilitate the removal of oil from the environment. In this study, we investigated to what extent absorbed oil was biodegraded and how this compared to the biodegradation of oil in water. To do so, we incubated two bacterial communities originating from the Niger Delta, an area subject to frequent oil spills, in the presence and absence of polypropylene particles. One community evolved from untreated soil whereas the second evolved from soil pre-exposed to oil. We observed that the polypropylene particles stimulated the growth of biofilms and enriched species from genera Mycobacterium, Sphingomonas and Parvibaculum. Cultures with polypropylene particles degraded more crude oil than those where the oil was present in suspension regardless of whether they were pre-exposed or not. Moreover, the community pre-exposed to crude oil had a different community structure and degraded more oil than the one from untreated soil. We conclude that the biodegradation rate of crude oil was enhanced by the pre-exposure of the bacterial communities to crude oil and by the use of oil-absorbing polypropylene materials. The data show that bacterial communities in the biofilms growing on the particles have an enhanced degradation capacity for oil.

Combined application of rhamnolipid and agricultural wastes enhances PAHs degradation via increasing their bioavailability and changing microbial community in contaminated soil

Either biosurfactants or agricultural wastes were frequently used to enhance degradation of PAHs in soil, but there is still not clear whether combined application of biosurfactants and agricultural wastes is more efficient. Rhamnolipid and/or agricultural wastes (mushroom substrate or maize straw) were mixed with PAHs-contaminated soil to explore their performances in the removal of PAHs. The present study showed that rhamnolipid combined with mushroom substrate (MR, 30.36%) or maize straw (YR, 30.76%) significantly enhanced the degradation of soil PAHs compared with single application of mushroom substrate (M, 25.53%) or maize straw (Y, 25.77%) or no addition (19.38%). The addition of agricultural wastes significantly (p < 0.001) enhanced concentration of dissolved organic carbon (DOC) in soil. The combined application obviously improved the bioavailability of PAHs in soils and exhibited synergistic effects on concentration of organic acid-soluble HMW PAHs and the degradation rate of total HMW PAHs. Meanwhile, the combined application significantly (p < 0.01) enhanced the abundance of dominant bacterial and fungal genera being connected with PAHs degradation. The removal rate of PAHs was positively correlated with the dominant genera of bacteria (r = 0.539-0.886, p < 0.05) and fungi (r = 0.526-0.867, p < 0.05) related to PAHs degradation. Overall, the combined application exhibited a better performance in the removal of PAHs in contaminated soil via increasing their bioavailability and changing microbial communities in soil.

Integration of biosorption and biodegradation in a fed-batch mode for the enhanced crude oil remediation

Microbial bioremediation of oil-contaminated sites is still a challenge due to the slower rate and susceptibility of microbes to a higher concentration of oil. The poor bioavailability, hydrophobicity, and non-polar nature of oil slow down microbial biodegradation. In this study, biodegradation of crude oil is performed in fed-batch mode using an oil-degrader Pseudomonas aeruginosa to address the issue of substrate toxicity. The slower biodegradation was integrated with faster biosorption for effective oil remediation. Highly fibrous and porous sugarcane bagasse was surface modified with hydrophobic octyl groups to improve the surface-oil interactions. The microbe showed 2 folds enhanced oil degradation in the fed-batch study, which was further increased by 1·5 folds in the integrated biosorption coupled biodegradation approach. The biosorption-assisted biodegradation approach supported the microbial growth to 2 folds higher than the fed-batch study without biosorbent. The analysis of biosurfactant production indicated the 3 folds higher concentration in fed-batch modes as compared to batch study. In the integrated strategy, the concentration of contaminant (oil) reduces to quite a tolerable level to microbes, which improved effective metabolism and thus overall biodegradation. This study puts forward a promising strategy for improved degradation of hazardous hydrophobic contaminants in a sustainable, economic and eco-friendly manner.

Sorption as a rapidly response for oil spill accidents: A material and mechanistic approach

Accidents involving oil transportation has increase due to directly connection with the elevation of global energy demand. The environmental losses are tremendous and brings huge economic issues to remediate the spilled oil. This report presents an up-to-date review on an overall aspects of oil spill remediation techniques, the fundamentals and advantages of sorption, the most applied materials through diverse types of oil spill sites and oils with variety features, highlight to natural materials and future prospective. As the environment preservation progressively becomes a major social concern issue, the achievement of a worldwide distribution process aligned with environmental legislation and economic viability is crucial to the oil industry. For this, a specific preparation considering several scenarios must be carried out regarding minimization of oil spillages. Since the sorbent materials are decisive for sorption, it was approached the main sorbents: natural, graphenic, nano, polymeric and waste materials, and future trends.

Self-cleaning of very heavily oil-polluted sites proceeds even under heavy-metal stress while involved bacteria exhibit bizarre pleomorphism

Two substrates saturated with crude oil, a desert soil sample (17.3% oil) and an olive-pomace (plant-based oil sorbent) sample (41% oil) showed effective self-cleaning via their own native microorganisms. The oil in such systems did not gather in one compact layer as it may be expected, but became dispensed as vesicles of varying dimensions connected together with narrow tunnels. Bacteria colonized the oil vesicles but only at the borders between the oil and the watery substrates. Through this architectural arrangement, the cells were capable of absorbing oil through their oil-contact surfaces and oxygen, water and water soluble nutrients through their substrate-contact surfaces. The cells involved were those of indigenous hydrocarbonoclastic bacterial communities. Many of those bacteria also tolerated and removed the amended heavy-metals, Hg²⁺, Cd²⁺, Pb²⁺, AsO₄^3- and AsO₃^3-. In the presence of heavy-metals, some of the bacterial species particularly of the pseudomonads exhibited bizarre pleomorphic cell-forms. It was concluded that even environments toxified with extremely high oil concentrations and heavy-metals can be remediated rather effectively via their already existing native microorganisms.

Bioaugmentation failed to enhance oil bioremediation in three soil samples from three different continents

Soil samples from Kuwait, Lebanon, Egypt and Germany were polluted with 3% crude oil. Series of samples were left unbioaugmented, others were bioaugmented with Kuwaiti desert soil with a long history of oil pollution and still others with Kuwaiti marine biofouling material. In the samples from Kuwait, Egypt, and Germany, bioaugmentation did not enhance oil removal, whereas it did in the sample from Lebanon. Taxa from the desert-soil bioaugmented batches, but none of those from the biofouling-material bioaugmented ones, succeeded in colonizing the four studied soils. The dynamics of the hydrocarbonoclastic communities during bioremediation were monitored. Those communities differed in composition, not only according to the type of soil, but also for the same soil; at various phases of bioremediation. Although each soil seemed to have its characteristic microflora, they all were similar in harboring lower and higher actinomycetes and pseudomonads in addition to many other taxa. None of the taxa prevailed through all phases of bioremediation. The most powerful isolate in oil-removal; was Rhodococcus erythropolis (Germany), and the weakest was Arthrobacter phenanthrenivorans (Lebanon). The pure hydrocarbonoclastic isolates tolerated unusually high oil concentrations, up to 30%.

Plant-based oil-sorbents harbor native microbial communities effective in spilled oil-bioremediation under nitrogen starvation and heavy metal-stresses

Cultivation on selective media revealed that the oil-sorbents, wheat straw, corncobs and sugarcane bagasse harbor hydrocarbonoclastic, diazotrophic and heavy metal-resistant microorganisms. Nitrogen-free media containing 1.0% crude oil lost between 32.2 and 37.5% of this oil, after 8 months when they have been inoculated with such microorganism-loaded sorbents. The used wheat straw, corncobs and sugarcane bagasse samples, 1.0 g each, absorbed respectively, 1.9, 1.1 and 2.5 g oil samples, and lost 24.3-39.2% of these amounts, after they had been incubated for 8 months. Total genomic DNA's from culture media and sorbents revealed various nitrogenase-coding nifH-genes. Pure hydrocarbonoclastic microbial isolates tolerated certain concentrations of, Hg²⁺, Cd²⁺, Pb²⁺, AsO₄^3- and AsO₃^3-. Some of those isolates even grew excellently with up to 1000 ppm of Pb²⁺ and 36,000 ppm of AsO₄^3- also in the presence of oil. Tested strains removed the tested heavy metals, Hg²⁺, Cd²⁺ and Pb²⁺ from the media and thus, reduced their toxicity against the hydrocarbon-degraders. It was concluded that plant-based sorbents, not only remove oil physically, but also harbor microbial communities effective in spilled oil-bioremediation under multiple stresses. Although each community consisted of one to three species only, the consortia which reached in numbers millions of CFU ml^-1 enrich the oily media with fixed nitrogen, and remove heavy metals which otherwise inhibit the oil-degrading microorganisms.

Enrichment of the soil microbial community in the bioremediation of a petroleum-contaminated soil amended with rice straw or sawdust

Two common organic wastes from agriculture (rice straw) and forestry (sawdust) were applied to a petroleum-contaminated soil to estimate their effectiveness in the removal of total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs). Rice straw was the more effective amendment than the other treatments in reducing TPH contents and addition of sawdust resulted in a significant decrease in PAH removal, particularly high-molecular-weight (5-6 ring) PAHs. Principal coordinates analysis (PCoA) indicates that rice straw treatment separated only the bacterial community but sawdust greatly affected both the soil bacterial and fungal communities. Moreover, the abundance of some petroleum degraders such as the bacteria Sphingomonas, Idiomarina and Phenylobacterium and the fungi Humicola, Wallemia and Graphium was promoted by inputs of the two agricultural and forestry wastes. These results highlight the potential of waste applications in accelerating hydrocarbon biodegradation which may be attributed to the enrichment of keystone taxa that show strong positive associations with hydrocarbon degradation.

Coliform Bacteria for Bioremediation of Waste Hydrocarbons

Raw, domestic sewage of Kuwait City contained about 106 ml-1 colony forming units of Enterobacter hormaechei subsp. oharae (56.6%), Klebsiella spp. (36%), and Escherichia coli (7.4%), as characterized by their 16S rRNA-gene sequences. The isolated coliforms grew successfully on a mineral medium with crude oil vapor as a sole source of carbon and energy. Those strains also grew, albeit to different degrees, on individual n-alkanes with carbon chains between C9 and C36 and on the individual aromatic hydrocarbons, toluene, naphthalene, phenanthrene, and biphenyl as sole sources of carbon and energy. These results imply that coliforms, like other hydrocarbonoclastic microorganisms, oxidize hydrocarbons to the corresponding alcohols and then to aldehydes and fatty acids which are biodegraded by β-oxidation to acetyl CoA. The latter is a well-known key intermediate in cell material and energy production. E. coli cells grown in the presence of n-hexadecane (but not in its absence) exhibited typical intracellular hydrocarbon inclusions, as revealed by transmission electron microscopy. Raw sewage samples amended with crude oil, n-hexadecane, or phenanthrene lost these hydrocarbons gradually with time. Meanwhile, the numbers of total and individual coliforms, particularly Enterobacter, increased. It was concluded that coliform bacteria in domestic sewage, probably in other environmental materials too, are effective hydrocarbon-biodegrading microorganisms.