Abstract
This study evaluated the effects of three commercial dispersants (Finasol OSR 52, Slickgone NS, Superdispersant 25) and three biosurfactants (rhamnolipid, trehalolipid, sophorolipid) in crude-oil seawater microcosms. We analysed the crucial early bacterial response (1 and 3 days). In contrast, most analyses miss this key period and instead focus on later time points after oil and dispersant addition. By focusing on the early stage, we show that dispersants and biosurfactants, which reduce the interfacial surface tension of oil and water, significantly increase the abundance of hydrocarbon-degrading bacteria, and the rate of hydrocarbon biodegradation, within 24 h. A succession of obligate hydrocarbonoclastic bacteria (OHCB), driven by metabolite niche partitioning, is demonstrated. Importantly, this succession has revealed how the OHCB Oleispira, hitherto considered to be a psychrophile, can dominate in the early stages of oil-spill response (1 and 3 days), outcompeting all other OHCB, at the relatively high temperature of 16 °C. Additionally, we demonstrate how some dispersants or biosurfactants can select for specific bacterial genera, especially the biosurfactant rhamnolipid, which appears to provide an advantageous compatibility with Pseudomonas, a genus in which some species synthesize rhamnolipid in the presence of hydrocarbons.
Highlights
Oil spills have been one of the primary inputs of pollution into the marine environment since the turn of the 20th century, when large oil tankers became prominent [1].The extraction, processing, and transportation of oil continues to increase, and new oil fields are regularly being discovered [2]
There was a reduction in the surface tension of seawater to 60.33 ± 1.25 mN m−1 when sophorolipid was added (Supplementary Figure S2), but a much greater effect was observed with all other dispersants and biosurfactants which reduced the surface tension to between 28 and 34 mN m−1
At day 1, no significant biodegradation of either alkanes or PAHs was observed in the oil-only controls or in microcosms treated with sophorolipid
Summary
Oil spills have been one of the primary inputs of pollution into the marine environment since the turn of the 20th century, when large oil tankers became prominent [1]. The extraction, processing, and transportation of oil continues to increase, and new oil fields are regularly being discovered [2]. Despite the COVID-19 pandemic, recent forecasts predict that global production and consumption of oil will return to pre-COVID-19 levels of ~100 million barrels per day by mid-2021 [3]. Oil pollution remains a significant threat to marine ecosystems, tourism, and fisheries. A key remediation tool in response to oil pollution is the application of dispersants [4]. The active surfactants within dispersants transform oil into small, stable droplets [5,6]
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