| چکیده انگلیسی مقاله |
Extended abstract
Background and objectives
Crude oil consists of aliphatic, aromatic, and heterocyclic compounds, all of which are toxic to life forms. Therefore, oil pollution is a significant environmental concern. Due to widespread use, accidental spills, transportation, and refining processes, crude oil contamination is relatively common worldwide. Methods for remediating oil-contaminated soils include biological, chemical, and physical approaches. While chemical and physical methods have many disadvantages, bioremediation is a promising and effective approach for treating oil-contaminated soils. Bioremediation is the natural ability of microorganisms and their enzyme systems to degrade, break down, and convert hydrocarbons into less toxic substances. This method is considered the least harmful and most cost-effective way to clean the environment. Different microbial genera are known to degrade hydrocarbons. Among these, Bacillus stands out as a Gram-positive, rod-shaped bacterium capable of producing spores in aerobic environments. Belonging to the class Bacilli and the family Bacillaceae, Bacillus can form endospores under stressful environmental conditions, allowing them to remain dormant for long periods. This unique characteristic makes Bacillus particularly advantageous for bioremediation in oil-contaminated environments. The current review article focuses on the recognition and potential of biodegradation of petroleum compounds by oil-eating bacteria, especially the genus Bacillus. It is hoped that this review will enhance our understanding of oil pollution's impact on biological communities and microbial remediation of oil-contaminated soils
Materials and Methods
All the articles used in this review were prepared from online sources (Google, Google scholar, SID, CAS, Science Direct, Wiley online Library, etc.), and from the publishers Elsevier, Wiley Online Library, Frontiers, Springer, ehp, Taylor and Francis Online, MDPI, ACS Publication, Nature, Civilica, etc.). This article is based on 169 JCR international journals and scientific journals. This review article briefly includes sections 1-The effect of crude oil on soil microorganisms, 2-Oil pollution in Iran, 3-The importance of bioremediation of petroleum compounds, 4-Mechanisms of remediation of oil-contaminated soils, 5-Aerobic and anaerobic degradation pathways of n-alkanes, 6-Researches conducted in the field of bioremediation of petroleum hydrocarbons in Iran, 7-Characteristics of Bacillus in oil degradation, and 8-Bioremediation of oil-contaminated soils in Iran with the approach of using Bacillus.
Results
Various bacterial genera, such as Achromobacter, Acinetobacter, Alcaligenes, Arthrobacter, Actinomycetes, Pseudomonas, Enterobacter, Micrococcus, Staphylococcus, Mycobacterium, Rhodococcus, Vibrio, Sphingomonas, Lactobacillus, and Serratia, are known to degrade hydrocarbons. These bacteria destroy hydrocarbons and purify the soil through the function of their enzyme system and secretion of various compounds such as biosurfactants through various pathways and mechanisms. There are two main mechanisms for the breakdown of hydrocarbons: aerobic and anaerobic pathways. In aerobic mechanisms, oxygen is used as the electron acceptor, while in anaerobic conditions, sulfate and nitrite receive the electrons and complete the process. Bacillus species are typically mesophilic, thriving at temperatures between 30-45°C. Some thermophilic species can grow at higher temperatures, up to 65°C. Spore formation in Bacillus involves asymmetric cell division, producing an endospore and a mother cell, which enables the bacterium to survive harsh conditions. Bacillus species can utilize hydrocarbons as carbon and energy sources, making them commonly found in oil-polluted soils. Several Bacillus species, including B. polymyxa, B. cereus, B. subtilis, B. badius, B. licheniformis, B. cibi, B. megaterium, and B. stearothermophilus, have demonstrated the ability to degrade petroleum hydrocarbons. These bacteria can tolerate a wide range of environmental conditions, such as varying pH, temperature, and salt concentrations, which few organisms can endure. They are highly resistant to environmental stressors like nutrient scarcity, dryness, radiation, hydrogen peroxide, and chemical disinfectants. The production of endospores also provides a distinct advantage for hydrocarbon biodegradation. Furthermore, Bacillus species produce a variety of biosurfactants, particularly lipopeptides, which enhance the solubility and bioavailability of hydrocarbons, thereby increasing bioremediation efficiency. Since biosurfactants are biodegradable and have low environmental toxicity, producing these powerful, stable compounds using low-cost carbon sources could significantly advance bioremediation of oil-contaminated soils. Bacillus also produces key degradative enzymes, such as lipase, hydroxylase, dioxygenase, monooxygenase P450, and protease, which play crucial roles in breaking down petroleum compounds. It has been reported that species like B. subtilis, B. pumilus, B. licheniformis, and B. megaterium can degrade alkanes, BTEX, and PAHs by secreting these enzymes. The hydrocarbon groups in oil can combine with soil phosphorus, leading to phosphorus depletion. Since phosphorus limitation is a key constraint in bioremediation of oil-contaminated soils, phosphorus-solubilizing Bacillus species such as B. subtilis, B. cereus, B. thuringiensis, B. pumilus, and B. megaterium, which secrete organic acids like gluconic, lactic, acetic, succinic, and propionic acids, can alleviate this problem. Research conducted in Iran and the international scientific community shows that this bacterium is capable of degrading various oil compounds by up to 99% within 10 to 30 days in liquid media. Additionally, in soil, Bacillus can degrade petroleum hydrocarbons by 20% to 80% over a period of 15 to 180 days.
Conclusion
In conclusion, various bacterial genera, particularly Bacillus species, play a critical role in the degradation of hydrocarbons through aerobic and anaerobic pathways. Bacillus, known for its resilience to environmental stressors and ability to form endospores, is highly effective in bioremediation, especially in oil-contaminated soils. These bacteria produce essential enzymes and biosurfactants, such as surfactin, which significantly enhance the breakdown of petroleum hydrocarbons. Moreover, phosphorus-solubilizing Bacillus species help address nutrient limitations in contaminated environments, further boosting their potential in environmental clean-up. Their remarkable efficiency, with degradation rates of up to 80% in soil, highlights their importance in sustainable bioremediation efforts worldwide. |