Chemical dispersants enhance the activity of oil- and gas condensate-degrading marine bacteria

Abstract

Application of chemical dispersants to oil spills in the marine environment is a common practice to disperse oil into the water column and stimulate oil biodegradation by increasing its bioavailability to indigenous bacteria capable of naturally metabolizing hydrocarbons. In the context of a spill event, the biodegradation of crude oil and gas condensate off eastern Canada is an essential component of a response strategy. In laboratory experiments, we simulated conditions similar to an oil spill with and without the addition of chemical dispersant under both winter and summer conditions and evaluated the natural attenuation potential for hydrocarbons in near-surface sea water from the vicinity of crude oil and natural gas production facilities off eastern Canada. Chemical analyses were performed to determine hydrocarbon degradation rates, and metagenome binning combined with metatranscriptomics was used to reconstruct abundant bacterial genomes and estimate their oil degradation gene abundance and activity. Our results show important and rapid structural shifts in microbial populations in all three different oil production sites examined following exposure to oil, oil with dispersant and dispersant alone. We found that the addition of dispersant to crude oil enhanced oil degradation rates and favored the abundance and expression of oil-degrading genes from a Thalassolituus sp. (that is, metagenome bin) that harbors multiple alkane hydroxylase (alkB) gene copies. We propose that this member of the Oceanospirillales group would be an important oil degrader when oil spills are treated with dispersant.

Metagenomic and metatranscriptomic responses of natural oil degrading bacteria in the presence of dispersants

“…However, all these studies, including this one, present some level of variation between successional patterns over time which reinforce the hypothesis that early and late microbial community assemblages are influenced by both deterministic and stochastic processes (Dini‐Andreote et al, ). However, when putting these taxonomic profiles in context with their corresponding oil degradation rates (Tremblay et al, ) Schreiber et al ., ), it appears that regardless of which oil degrading microbes are present, oil is being degraded.…”

“…Usage of dispersant in oil spills remains controversial (Kleindienst et al, ). Some recent studies suggest that dispersants enhance oil degradation rates (Tremblay et al, ), whereas others found a negative impact (Kleindienst et al, ) or no impact (Brakstad et al, ). We previously reported that adding dispersant to oil slightly favoured n ‐alkane degradation in east coast microcosms (Tremblay et al, ) and did not have a significant impact in west coast microcosms (Schrieber et al , submitted).…”

“…Some recent studies suggest that dispersants enhance oil degradation rates (Tremblay et al, ), whereas others found a negative impact (Kleindienst et al, ) or no impact (Brakstad et al, ). We previously reported that adding dispersant to oil slightly favoured n ‐alkane degradation in east coast microcosms (Tremblay et al, ) and did not have a significant impact in west coast microcosms (Schrieber et al , submitted). Even if addition of dispersant to oil does not necessarily have an impact on oil degradation, we show here that adding dispersant to oil microcosms does result in modulating microbial community structure (Fig.…”

“…). Thalassolituus was previously shown to proliferate in the presence of dispersant (Tremblay et al, ). Oleispira is known to reside in cold seawater (Yakimov et al, , ), and we also observed this microorganism in our winter microcosms.…”

“…By making use of high throughput sequencing technology, recent efforts from our group have focused on understanding the dynamics of oil degrading microbial communities on Canadian coasts with an emphasis on the evaluation of the effect of adding chemical dispersants on oil biodegradation rates. We have shown that the addition of dispersant to oil enhances n-alkane degradation rates in microcosms from the east coast (Tremblay et al, 2017) but had little effect in west coast microcosms (Schrieber et al, 2019). This latter study reports oil degrading data observed in the west coast microcosms for which we present the corresponding shotgun metagenomic and metatranscriptomic sequencing data in this study.…”