Evaluation of autochthonous bioaugmentation and biostimulation during microcosm-simulated oil spills
Introduction
The recent Deep Horizon oil spill accident in the Gulf of Mexico provided an alert and a reminder that despite the stricter environmental regulations that have been adopted by most countries, oil spills still remain as a serious risk to marine ecosystems. In both socioeconomic and ecological terms, the impact of an oil spill on the marine environment can be quite significant. Most importantly, the loss of species richness, downgraded sediment quality and further negative impacts on offshore fish and crustacean fisheries represent a subset of the side effects of oil spills (Kirby and Law, 2008).
Conventional first response actions, such as physical removal with booms, skimmers and absorbent materials, cannot achieve complete clean-up of oil spills and must be deployed shortly after the oil spill occurs. However, when applicable, the use of chemical dispersants is only allowed when the coastline depth is at least 15 m due to their potential toxic effects on marine organisms; otherwise, their overall effectiveness is questionable.
In past years, bioremediation has emerged as an effective and environmentally friendly treatment for shorelines contaminated as a result of marine oil spills. The majority of compounds in crude oil and refined products are biodegradable and will eventually be removed from the environment through consumption by microbes. Enhanced bioremediation aims to stimulate the rate of this process with the following two complementary approaches: bioaugmentation and biostimulation. In bioaugmentation, the addition of oil-degrading bacteria boosts biodegradation rates, whereas in biostimulation, the growth of indigenous hydrocarbon degraders is stimulated by the addition of nutrients (mainly N and P) or other growth-limiting nutrients (Nikolopoulou and Kalogerakis, 2010).
Although the effectiveness of bioaugmentation in the marine environment is still under investigation, the addition of oil-degrading microorganisms has been proposed as a bioremediation strategy. Crude oil is composed of a wide range of different compounds, which makes it difficult for the indigenous population to cope with this broad variety of substrates, and hence, oil-degrading microorganisms could be added to supplement the indigenous population (Leahy and Colwell, 1990).
Although laboratory studies on bioaugmentation have shown an enhancement of oil biodegradation, the effectiveness of bioaugmentation has not been convincingly demonstrated in the field. Most of the field studies conducted thus far suggest that bioaugmentation is not effective in significantly enhancing oil biodegradation for most environments in the long run (Nikolopoulou and Kalogerakis, 2011). Generally, in most environments, it appears that indigenous oil-degrading microorganisms can degrade oil if they are not limited by the prevailing environmental conditions. Case studies support the potential of bioaugmentation as a remediation strategy to combat oil spills, but this promising technology is still in the experimental stage (El Fantroussi and Agathos, 2005).
There is increasing evidence that the best approach for overcoming these barriers is the use of microorganisms from the polluted area. A new concept in bioaugmentation, known as “autochthonous bioaugmentation” (ABA), has been proposed by Ueno et al. (2007) and is defined as a bioaugmentation technology that exclusively uses microorganisms indigenous to the sites (soil, sand, and water) slated for decontamination. Isolated single strains or enriched cultures, which are obtained “before” or “after” the contamination of the target sites, are administered to the sites once contamination occurs. The key concept is to conduct the enrichment of contaminant-degrading bacteria under the same or similar conditions as those present where the bioaugmentation will be performed. The ABA approach uses autochthonous microbial consortia or isolates that are highly enriched and much better adapted to chronically or artificially contaminated environments (Hosokawa et al., 2009). The success of oil spill bioremediation depends on the establishment and maintenance of physical, chemical and biological conditions that favor enhanced oil biodegradation rates in the marine environment. Through biostimulation, the growth of indigenous oil degraders is stimulated by the addition of nutrients (Nitrogen and Phosphorous) or other growth-limiting co-substrates and/or by alterations in environmental conditions (e.g., surf-washing, oxygen addition by plant growth, etc.). In this study, we examined the capabilities of an acclimated indigenous microbial consortium (ABA) sampled from a pristine environment in the presence or absence of other rate limiting factors (i.e., nutrients and biosurfactants) (biostimulation) as a potential strategy for the successful remediation of polluted marine environments.
Section snippets
Experimental design
In this study, we examined the effectiveness of autochthonous bioaugmentation together with biostimulation versus biostimulation-only strategies for the successful remediation of polluted marine environments. Seawater was collected from a pristine environment in the Eastern Mediterranean Sea (Agios Onoufrios Beach, Chania, Crete) and was placed in a bioreactor with 1% v/v crude oil to grow and adapt the indigenous population for later use of this consortium for bioaugmentation purposes. Crude
Results and discussion
Evaluation of the effectiveness of each treatment on the crude oil biodegradation rate was estimated in terms of alkanes, PAHs and the compositional changes of the hydrocarbon degraders throughout the period of the experiment. Fig. 2 represents the total depletion rate of the saturated fraction of n-alkanes (C14–C35) of the control treatment (C) as well as of the NPK, NPKM, NPKMR, ULR and ULRM treatments at different time intervals of the experiment. The control had no significant effect on the
Acknowledgments
This work was funded by FP-7 PROJECT No. 266473, “Unravelling and exploiting Mediterranean Sea microbial diversity and ecology for xenobiotics’ and pollutants’ clean up” – ULIXES and by the European Union (European Social Fund – ESF) and Greek national funds through the Operational Program “Education and Lifelong Learning” of the National Strategic Reference Framework (NSRF) – Research Funding Program: Heracleitus II, Investing in knowledge society through the European Social Fund.
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2023, International Biodeterioration and BiodegradationCitation Excerpt :Bioremediation is widely used to treat petroleum hydrocarbon pollution (Dindar et al., 2013; Wu et al., 2016), via two main approaches: bioaugmentation with pre-grown bacteria (single strains or consortia) that are specialized in degrading the target pollutants (Tyagi et al., 2011), or biostimulation, which involves modifying the environment to create preferred growth conditions for native degrading bacteria, such as the amendment of oxygen, nutrients, and other supplementary components (Benyahia and Embaby, 2016). Autochthonous bioaugmentation, using indigenous hydrocarbon-degrading isolates to amend the contaminated soil (Mohammed et al., 2007), combined with nutrient addition can potentially increase bioremediation efficiency (Ueno et al., 2007; Nikolopoulou et al., 2013). The bioavailability of petroleum carbon components is limited due to their hydrophobicity (Cerniglia, 1992) and low water solubility (Weissenfels et al., 1992), making bioremediation exceptionally challenging in hot and dry desert ecosystems.