One of the major environmental problems today is hydrocarbon contamination resulting from the activities related to the petrochemical industry. Accidental releases of petroleum products are of particular concern in the environment. Hydrocarbon components have been known to belong to the family of carcinogens and neurotoxic organic pollutants. Currently accepted disposal methods of incineration or burial insecure landfills can become prohibitively expensive when amounts of contaminants are large. Mechanical and chemical methods generally used to remove hydrocarbons from contaminated sites have limited effectiveness and can be expensive. Bioremediation is the promising technology for the treatment of these contaminated sites since it is cost-effective and will lead to complete mineralization. Bioremediation functions basically on biodegradation, which may refer to complete mineralization of organic contaminants into carbon dioxide, water, inorganic compounds, and cell protein or transformation of complex organic contaminants to other simpler organic compounds by biological agents like microorganisms. Many indigenous microorganisms in water and soil are capable of degrading hydrocarbon contaminants. This paper presents an updated overview of petroleum hydrocarbon degradation by microorganisms under different ecosystems.

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Microbial Degradation of Petroleum Hydrocarbon Contaminants: An Overview

Increasing public awareness of environmental pollution influences the search and development of technologies that help in clean up of organic and inorganic contaminants such as hydrocarbons and metals. An alternative and eco-friendly method of remediation technology of environments contaminated with these pollutants is the use of biosurfactants and biosurfactant-producing microorganisms. The diversity of biosurfactants makes them an attractive group of compounds for potential use in a wide variety of industrial and biotechnological applications. The purpose of this review is to provide a comprehensive overview of advances in the applications of biosurfactants and biosurfactant-producing microorganisms in hydrocarbon and metal remediation technologies.

https://www.mdpi.com/1422-0067/12/1/633/pdf

Environmental applications of biosurfactants: Recent advances

Fitzpatrickʼs Dermatology in General Medicine

http://envismadrasuniv.org/Bioremediation/pdf/Crude%20petroleum%20oil%20biodegradation.pdf

Crude petroleum-oil biodegradation efficiency of Bacillus subtilis and Pseudomonas aeruginosa strains isolated from a petroleum-oil contaminated soil from North-East India

A field experiment was conducted in Delaware (USA) to evaluate three crude oil bioremediation techniques. Four treatments were studied: no oil control, oil alone, oil + nutrients, and oil + nutrients + an indigenous inoculum. The microbial populations were monitored by standard MPN techniques, PLFA profile analysis, and 16S rDNA DGGE analysis for species definition. Viable MPN estimates showed high but steadily declining microbial numbers and no significant differences among treatments during the 14-weeks. Regarding the PLFA results, the communities shifted over the 14-week period from being composed primarily of eukaryotes to Gram-negative bacteria. The Gram-negative communities shifted from the exponential to the stationary phase of growth after week 0. All Gram-negative communities showed evidence of environmental stress. The 16S rDNA DGGE profile of all plots revealed eight prominent bands at time zero. The untreated control plots revealed a simple, dynamic dominant population structure throughout the experiment. The original banding pattern disappeared rapidly in all oiled plots, indicating that the dominant species diversity changed and increased substantially over 14 weeks. The nature of this change was altered by nutrient-addition and the addition of the indigenous inoculum.

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Microbial Population Changes During Bioremediation of an Experimental Oil Spill

Factors affecting biosurfactant production by oil degrading Aeromonas spp. isolated from a tropical environment

Crude oil degradation was observed in water samples from three sites along the course of a polluted stream in Lagos, Nigeria. Consistent increase and decrease in the total viable counts (TVCs) of indigenous organisms occurred in the test and control experiments, respectively. Enrichments of the water samples with crude oil resulted in the isolation of nine bacteria belonging to seven genera. A mixed culture was developed from the assemblage of the nine species. The defined microbial consortium utilized a wide range of pure HCs including cycloalkane and aromatic HCs. Utilization of crude oil and petroleum cuts, i.e., kerosene and diesel resulted in an increase in TVC (till day 10) concomitant with decreases in pH and residual oil concentration. Crude oil, diesel and kerosene were degraded by 88, 85 and 78%, respectively, in 14 days. Substrate uptake studies with axenic cultures showed that growth was not sustainable on either cyclohexane or aromatics while degradation of the petroleum fractions fell below 67% in spite of extended incubation period (20 day). From the GC analysis of recovered oil, while reductions in peaks of n-alkane fractions and in biomarkers namely n-C17/pristane and n-C18/phytane ratios were observed in culture fluids of pure strains, complete removal of all the HC components of kerosene, diesel and crude oil including the isoprenoids was obtained with the consortium within 14 days.

Microbial degradation of petroleum hydrocarbons in a polluted tropical stream

Pseudomonas sp. strain LP1, an organism isolated on the basis of its ability to grow on pyrene, was assayed for its degradative and biosurfactant production potentials when growing on crude, diesel and engine oils. The isolate exhibited specific growth rate and doubling time of 0.304 days−1 and 2.28 days, respectively on crude oil (Escravos Light). The corresponding values on diesel were 0.233 days−1 and 2.97 days, while on engine oil, were 0.122 days−1 and 5.71 days. The organism did not show significant biosurfactant production towards crude oil and diesel, but readily produced biosurfactant on engine oil. The highest Emulsification index (E24) value for the biosurfactant produced by LP1 on engine oil was 80.33 ± 1.20, on day 8 of incubation. Biosurfactant production was growth-associated. The surface-active compound which exhibited zero saline tolerance had its optimal activity at 50°C and pH 2.0.

Degradation of hydrocarbons and biosurfactant production by Pseudomonas sp. strain LP1

Experiments were conducted to investigate soil quality changes resulting from a single application of selected fungicides at the following rates 2, 10, 20, 200 and 1000 μg g −1 dry soil and 1, 5, 10, 100, 1000 μg g −1 dry soil and for metalaxyl and mefenoxam its R-enantiomer, respectively. Microbial activity indices (available N, ammonification and nitrification rates, microbial population density and specific enzymatic systems) were the more sensitive indicators of change. The values of these indicators generally increased with the period of incubation and decreased or increased at high rates. Mefenoxam and metalaxyl and their major acid metabolites were toxic to soil micro-organisms at high doses with 16 h-IC 50 values of 4500, 12,500, and 15,800 μg g −1 soil (dry weight), respectively. Thus, their ranking in terms of acute toxic effects was in the order mefenoxam>metalaxyl>acid metabolite. Incorporation of the fungicides in soil resulted in increased ammonium and nitrate levels. These changes stimulated soil microbial activity as evidenced by increased ammonification and nitrification rates, increased total viable bacteria counts especially after short-term exposure. Of the enzyme activities studied, dehydrogenase activity was the most sensitive to fungicides. This sensitivity was more pronounced with metalaxyl on long-term exposure. In general, the stimulation of nitrogen transformation and bacterial density were more pronounced with mefenoxam.

Soil quality changes resulting from the application of the fungicides mefenoxam and metalaxyl to a sandy loam soil

In an effort at developing active microbial strains that could be of relevance in bioremediation of petroleum contaminated systems in Nigeria, fifteen hydrocarbon degrading bacteria and fungal species were isolated from three bitumen deposits. The predominant species belonged to the genera Pseudomonas and Aspergillus. The ability of Pseudomomnas stutzeri, Pseudomonas mullei and Alcaligenes sp. to degrade naphthalene, kerosene and diesel was studied. The results show maximal increase in optical densities and total viable counts concomitant with decrease in pH of the culture media. Typical generation times vary between 0.64 and 1.09 d, 0.97 and 3.03 d, 0.88 and 2.97 d respectively for kerosene, diesel and naphthalene. All the isolates utilized the hydrocarbons as sole carbon and energy sources equally well; there was no statistical difference (P > 0.05) in the utilization rates, thus suggesting close genetic similarities in respect of oil degradation capabilities. The study revealed for the first time, the types of microorganisms that are associated with Nigerian bitumen deposit and their potential to degrade oil. The knowledge of the potentials of these isolates to degrade hydrocarbons will increase the possibilities of developing models and strategies for removing hydrocarbon pollutants from the environment. (Nature and Science. 2006;4(3):51-57).

Matthew O. Ilori

Papers

Factors affecting biosurfactant production by oil degrading Aeromonas spp. isolated from a tropical environment

Microbial degradation of petroleum hydrocarbons in a polluted tropical stream

Degradation of hydrocarbons and biosurfactant production by Pseudomonas sp. strain LP1

Soil quality changes resulting from the application of the fungicides mefenoxam and metalaxyl to a sandy loam soil

Hydrocarbon degrading potentials of bacteria isolated from Nigerian bitumen (Tarsand) deposit