Marine microbes rapidly adapt to consume ethane, propane, and butane within the dissolved hydrocarbon plume of a natural seep

Abstract

Simple hydrocarbon gases containing two to four carbons (ethane, propane, and butane) are among the most abundant compounds present in petroleum reservoirs, and are introduced into the ocean through natural seepage and industrial discharge. Yet little is known about the bacterial consumption of these compounds in ocean waters. To assess the timing by which microbes metabolize these gases, we conducted a three-phase study that tested and applied a radiotracer-based method to quantify the oxidation rates of ethane, propane, and butane in fresh seawater samples. Phase 1 involved the synthesis of tritiated ethane, propane, and butane using Grignard reagents and tritiated water. Phase 2 was a systematic assessment of experimental conditions, wherein the indigenous microbial community was found to rapidly oxidize ethane, propane, and butane. Phase 3 was the application of this tritium method near the Coal Oil Point seeps, offshore California. Spatial and temporal patterns of ethane, propane, and butane oxidation down current from the hydrocarbon seeps demonstrated that >99% of these gases are metabolized within 1.3 days following initial exposure. The oxidation of ethane outpaced oxidation of propane and butane with patterns indicating the microbial community responded to these gases by rapid adaptation or growth. Methane oxidation responded the slowest in plume waters. Estimates based on the observed metabolic rates and carbon mass balance suggest that ethane, propane, and butane-consuming microorganisms may transiently account for a majority of the total microbial community in these impacted waters.

Widespread methane seepage along the continental margin off Svalbard - from Bjørnøya to Kongsfjorden

“…The derived δ 13 C-sources with an estimated stable carbon isotopic composition of −64 to −80‰, coupled with a lack of detection of any higher hydrocarbons, point to microbial generated methane 56 for the Svalbard plume. However, we do not discount the possibility that higher hydrocarbons could have been removed by migration 57 or preferential microbial oxidation 58 . Oxidative trends could only be fitted to part of the data, therefore in the northern regions there might be less overprinting by microbial oxidation than we estimated for the southern regions.…”

The Distribution of Dissolved Methane and Its Air-Sea Flux in the Plume of a Seep Field, Lingtou Promontory, South China Sea

“…It is concluded that the methane originally discharged at the seafloor was oxidized before sampling. However, we do not discount the possibility that the methane could have been removed by migration or preferential microbial oxidation [58,59].…”

Methane oxidation in the eastern tropical North Pacific Ocean water column

“…Several improvements to both the 3 H and LL 14 C methods can be recommended for future MO x rate measurements. The 3 H method background can be better quantified using killed control samples as method blanks (either to subtract from rate samples or set a detection limit [e.g., Mendes et al, 2015]). For this, it is important to treat the killed controls in such a manner that the microbial activity is arrested well before the tracer is added.…”