|Nur Zaida Zahari||Faculty of Science & Natural Resources, Universiti Malaysia Sabah, UMS Road, 88400 Kota Kinabalu, Sabah, Malaysia|
|Gan Poh Yan||Faculty of Science & Natural Resources, Universiti Malaysia Sabah, UMS Road, 88400 Kota Kinabalu, Sabah, Malaysia|
|Sahibin Abd Rahim||Faculty of Science & Natural Resources, Universiti Malaysia Sabah, UMS Road, 88400 Kota Kinabalu, Sabah, Malaysia|
A bioremediation study was undertaken to assess the biodegradation efficiency of crude oil in seawater using two locally isolated strains namely Candida tropicalis RETL-Cr1 and Pseudomonas aeruginosa BAS-Cr1. The inoculation was carried out using single strains labelled as T1; Candida tropicalis RETL-Cr1, T2; single strain Pseudomonas aeruginosa BAS-Cr1 and T3; mixture of both cultures respectively. The biodegradation capability of each strain was examined in a shake-flask culture at 30?C, agitated at 200 rpm for 28 days. The growth profile was monitored by measuring the optical density (OD600) using spectrophotometry. The biodegradation efficiency of crude oil was quantified by comparing the initial and final crude oil concentrations, whereas the degradation of selected aliphatic hydrocarbons was quantified using gas chromatography-mass spectrometry (GC-MS) by comparing the initial and final area in chromatograms. The present finding showed that in 5% (v/v) of crude oil, consortia cultures had the highest degradation, with 50%, while single cultures of C. tropicalis RETL-Cr1 and P. aeruginosa BAS-Cr1 achieved 39% and 27%, respectively. The results of biodegradation showed that consortia cultures experienced 1.3-fold higher compared to a single culture of C. tropicalis RETL-Cr1 and 2-fold higher compared to a single culture of P. aeruginosa BAS-Cr1. Based on GC-MS analysis, the aliphatic hydrocarbons were found degraded through the treatment with the highest degradation recorded in consortia cultures: octadecane (73.93%) > eicosane (73.23%) > nonadecane (70.43) > docosane (67.64%) > heptadecane (66.36%) > heneicosane (65.94%) > tricosane (62.28%). From the results obtained, it can be concluded that the potency of microbes as excellent hydrocarbon degraders is as follows: consortia (mixed of two species) > C. tropicalis RETL-Cr1> P. aeruginosa BAS-Cr1. This supports the idea that microbial communities, especially in mixtures, have the ability to degrade hydrocarbon contaminants more effectively and can be environmentally friendly due to their specific ability to metabolize hydrocarbons.
Biodegradation; Crude oil; Seawater; Single and consortia cultures
Nowadays, oil spill incidents in the marine environment have become a major threat to ecosystems. It has been reported that marine transportation and activities are the major reasons for petroleum oil tankers bringing oil produced to Northeast Asia (Jaswar & Maimun, 2014). Due to rapid economic development and land-based activities in the marine environment, the release of these complex substances into seawater will immediately be subject to a variety of physical, chemical, and biological weathering processes. This will have a tremendous effect on ecosystems, and the impacts will continue even after the visible oil has been removed or dispersed in the environment. The impacts include obvious immediate consequences; for instance, widespread animal mortality due to toxic effects, and more subtle long-term effects on human health, marine organisms, wetland ecosystems, and coral reefs. Numerous studies have documented that the toxicity of crude oil adversely affects people inhabiting areas affected by oil spills through either direct or indirect contact. This is because the oil can produce compounds with mutagenic and carcinogenic properties. These properties can affect the skin, blood, immune system, and other organs (Ubani et al., 2013). Due to the above-mentioned hazards, it is essential to detoxify or treat such oil-contaminated marine water using various techniques. A number of approaches and technologies have been developed for controlling and clearing oil spills in seawater, including physical, chemical, thermal, and biological remediation technologies (Dave & Ghaly, 2011). The feasibility of these current remediation technologies depends on various elements, such as the type and volume of spilled oil, the temperature of the water body, and the environmental conditions of the contaminated site (Garapati, 2012). Biodegradation, also known as bioremediation, is a very broad field and the most reliable mechanism for eliminating organic and inorganic pollutants from the environment by using microorganisms (Budhijanto et al., 2015; Komala et al., 2013; Thakur & Srivastava, 2011). This method transforms pollutants into harmless metabolites or completely mineralizes them into carbon dioxide and water (Ikhimiukor & Nneji, 2014; Khelil et al., 2014). Scientists have found that crude oil can be degraded faster by using more cost-effective and environmentally friendly treatment technologies for the remediation of hydrocarbons by using hydrocarbon-degrading microorganisms (Garapati, 2012). In the case of marine oil spills, especially in Sabah, Malaysia, there is little information and research on the biodegradation of hydrocarbons. There is also very limited information on identified local species of microorganisms that have the potential to degrade hydrocarbons. Therefore, this paper will emphasize two selected environmentally relevant microorganisms (ERM), namely Candida tropicalis RETL-Cr1 and Pseudomonas aeruginosa BAS-Cr1, in degrading crude oil in seawater environments. The study will focus on the potential of both microorganisms as single and consortia cultures (i.e., mixtures of both strains) on the biodegradation efficiency of different classes of petroleum hydrocarbon compounds. This research also attempts to evaluate the possible improvement capability of biological methods as useful tools in developing different strategies for the removal of hydrocarbons from the marine environment.
Based on this study, it can be concluded that the reduction of hydrocarbons by both single and consortia cultures varies. Consortia cultures displayed high degradation of hydrocarbon, which was 2-fold higher as compared to the single culture of C. tropicalis RETL-Cr1 and of P. aeruginosa BAS-Cr1, respectively. This has been proven with chromatogram profiles, where the crude oil element has been degraded and undergoes emulsification activity. The results concluded that consortia cultures have great potential for microbial-enhanced oil recovery in real field sites, especially in polluted marine water. To advance biodegradation studies, future research should focus on treatment with high concentrations of crude oil and carry out biocompatibility tests of two different species to identify the presence of toxins or any potentially harmful effects among the consortia cultures.
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