In this work we study the microbial communities after a port oil spill

In 2019, bunkering operations inside a Portuguese maritime port (SW) led to a fuel oil leakage. Five days after the incident, contaminated seawater and fuel samples were collected and used in laboratory experiments, aiming to (i) survey the native microbial community response to the spilled fuel; and (ii) evaluate if the hydrocarbon-degrading activity could be accelerated through bioaugmentation with a lyophilized bacterial consortium (Rhodococcus erythropolis, Pseudomonas sp.). Two parallel experiments were assembled for 30 days, in a seawater/oil ratio of 20:0.5 and continuous agitation, namely: (i) an enrichment experiment (seawater+oil+nutrients) to describe the succession of the microbial community composition by Next-Generation Sequencing (NGS); and (ii) a microcosm experiment, with 3 treatments - natural attenuation (seawater + oil), biostimulation (seawater + oil + nutrients), and bioaugmentation (seawater + oil + nutrients + lyophilized consortium), to assess differences in the abundance of hydrocarbon-degrading microorganisms, by the most probable number method, and removal of total petroleum hydrocarbons, accessed by FT/IR. In addition, for both experiments, samples were also collected for bacterial strains isolation in culture media. Results have shown a shift in the microbial communities, with a decrease in diversity and an increase in the abundance of hydrocarbon-degrading taxa (e.g. Alcanivorax and Thalassospira). Overall, 95 bacterial strains were isolated from both experiments, including 5 species previously described as obligate hydrocarbonoclastic bacteria and key groups represented in the enriched communities. While the lyophilized bacteria added in bioaugmentation, enhanced the abundance of hydrocarbons-degraders over time and were recovered until the 1st (for Pseudomonas sp.) and 3rd week (for Rhodococcus erythropolis) the microcosm experiment, it was the addition of nutrients that favoured the biodegradation process, since after 15 days, the percentage of TPHs removal was significantly higher in the biostimulation (~ 69%) and bioaugmentation (~ 63%) treatments, when compared to natural attenuation. In sum, the present work highlights the role of biostimulation in degrading a fuel spillage and underlines the potential of combining bioremediation with the already employed remediation techniques inside maritime ports, to tackle spills.