BIOREMEDIATION: A KEY TO TREAT HYDROCARBON AND PETROLEUM PRODUCTS IN SOIL

Hydrocarbon contamination is a serious environmental problem nowadays resulting from the activities of the petrochemical industry. Petroleum products are the primary concerns that are accidentally released in the environment. Generally, several methods are used to remove hydrocarbons from contaminated soil which have limited effectiveness and also can be expensive. Bioremediation is the eco-friendly technology for the treatment of these contaminated soils since it is cost-effective and leads to complete mineralization. Bioremediation functions depend on biodegradation by microorganisms, which may refer to the complete mineralization of organic contaminants into the inorganic compounds, cell protein, water, and carbon dioxide. It also includes the transformation of complex organic contaminants to other simpler organic compounds by biological agents like microorganisms and plants. It is very important to understand that this kind of waste remediation uses no toxic chemicals, although in some certain circumstances it may use a microorganism that can not be harmful. In recent research bioremediation of crude petroleum-contaminated soil has already been investigated. Microbial treatment of oil well system and reservoir to control paraffin deposition is one of the efficient enhanced oil removal methods. In this review, our main focus is on the degradation of hydrocarbon and petroleum pollutants by microorganisms such as Bacillus cereus, Pseudomonas aeruginosa, Micrococcus luteus, and Aspergillus sp.

                                                                                                                   

Petroleum products

Petroleum products, which is a complex mixture of organic molecules such as hydrocarbons are the major energy source. It is composed of carbon and hydrogen. Basically, three types of hydrocarbons i.e. Saturated hydrocarbons- single-bonded (alkanes, cycloalkanes), Unsaturated hydrocarbons- double-bonded or triple-bonded (alkenes, alkyne), Aromatic hydrocarbons- at least having one aromatic ring.

 

Petroleum products example- diesel, crude oil, etc.

 

Forms of hydrocarbons- Gases- methane, propane, Liquids- hexane, benzene, Waxes, or Low melting solids- paraffin, wax, naphthalene, Polymers- polyethylene, polypropylene, polystyrene.

Hydrocarbons lack phosphorus and nitrogen, so it shows limited degradation.

Effects of petroleum contamination in the soil- loss of species, economic loss, human health-aromatic hydrocarbon causes cancer, irritation in the respiratory tract, asthma, allergies, carcinogenic to lungs, global warming, acid rain, ozone depletion.

Bioremediation of petroleum products in soil: A three corner process

Use of biological organisms, such as bacteria, fungi, and plants, to reduce or eliminates toxic pollutants from contaminated sites by degradation, assimilation or transpiration in the atmosphere is called bioremediation.

Hydrocarbon is degraded by a variety of  microorganisms and they influenced the rate of nutrient recycling, and even the release of biosurfactants. Some microorganisms remediate hydrocarbons including bacteria and fungi such as Bacillus cereus, Pseudomonas aeruginosa, Micrococcus luteus, and Aspergillus sp. Microorganisms can use petroleum hydrocarbons as carbon and energy sources, which are converted into carbon dioxide and water or low- toxic or  nontoxic materials. 

Strategies of bioremediation- 

• Bioaugmentation- adding particular microorganisms in contaminated sites to breakdown the toxic component.
• Biostimulation- adding nutrients for native microorganisms in contaminated sites to breakdown the toxic component.

Pseudomonas aeruginosa L10 (Endophytes)

A hydrocarbon-degrading, biosurfactant-producing, plant-growth-promoting, and endophytic Pseudomonas aeruginosa L10 has been isolated from the roots of a reed (Phragmites australis) that grows in high-salinity oil-polluted areas of the Yellow River Delta, Shandong, China. Bacterial endophytes Pseudomonas aeruginosa L10 with the capacity to degrade petroleum hydrocarbons and promote plant growth may facilitate phytoremediation for the removal of petroleum hydrocarbons from contaminated soils. Pseudomonas aeruginosa L10 is a Gram-negative, rod-shaped bacterium.

 

Petroleum hydrocarbons degradation by Pseudomonas aeruginosa L10

Endophytic bacteria Pseudomonas aeruginosa L10 shows plant-microbe based remediation (Phytoremediation)

The combined use of plants and bacteria, based on the synergistic activities of plants and their associated microbes called phytoremediation, enhances the efficiency of remediation of soil contaminated with organic pollutants. In the plant-microbe-based remediation system, plants provide residency and nutrients to their associated endophytic and rhizosphere bacteria. In return, the bacteria support plant growth by the degradation and detoxification of hydrocarbons. Moreover, they improve plant growth and health due to their innate plant growth-promoting mechanisms. Plants may take up hydrocarbons from the soils and translocate in their different tissues in which endophytic bacteria reside.  A major advantage of endophytic bacteria over rhizobacteria or soil bacteria is that they reside in internal tissues of the host plant and hence have less competition for nutrients and space. Endophytic bacteria have a greater capacity to enhance petroleum hydrocarbon phytoremediation than rhizosphere or soil bacteria. 

The genome of Endophytic Pseudomonas aeruginosa L10

• Putative genes encoding with monooxygenase, deoxygenase, alcohol dehydrogenase, aldehyde dehydrogenase.

• n-alkane degradation genes encoding with alkane-1-monooxygenase.

• Rhamnolipid biosynthesis genes show biosurfactant activity, it is an amphiphilic compound produce on microorganisms surface reduce surface and interfacial tension in the fluid phase.

• 1-aminocyclopropane 1 carboxylic (ACC) deaminase gene promotes the biosynthesis of the plant hormone.

• Tryptophan biosynthesis genes or indole-3-acetic acid (IAA) synthesis genes promote plant growth and play a role as a source of carbon, nitrogen, and energy for plants.

• Biosynthesis of siderophore genes, two clusters of genes i.e. pyoverdine siderophore genes and pyochelin siderophore genes it is an iron-chelating compound transport iron and eliminates toxic heavy metals.

Other microorganisms used in bioremediation of hydrocarbon and petroleum products

 

Conclusion

·         The endophyte P. aeruginosa L10 degrades petroleum hydrocarbons produce biosurfactants and promote plant growth of Phragmites australis.

·         We observed that P.aeruginosa L10 needs more research for further studies of the industrial and environmental applications.

·         B.cereus strain a potential tool for bioremediation and microbial enhanced oil recovery purposes.

·         M.luteus BN56 produced biosurfactants (glycolipid and  trehalose tetraester) on hydrocarbon substrates with high effectiveness, so the strain well suited for bioremediation of hydrocarbon contaminated soil.

·         Aspergillus sp. RFC-1 can adsorb, absorb, and degrade crude oil and the three types of  Polycyclic Aromatic Hydrocarbons (PAHs) i.e. naphthalene, phenanthrene, and pyrene.

·         Plant-microbe-based remediation system (phytoremediation) is advantageous over microbial remediation considering their economic feasibility, widespread pollution degradation capacity, higher public acceptance and also a high rate of contaminant reduction or degradation.

In recent, the 20,000 tones of oil accidentally spill in Russia, Siberia, Arctic River which is one of the major problems. So we should need to focus on the bioremediation techniques to remove these types of toxic contaminants from different types of  contaminated sites.