The Impact of Methane on Microbial Communities at Marine Arctic Gas Hydrate Bearing Sediment

Abstract

Cold seeps are characterized by high biomass, which is supported by the microbial oxidation of the available methane by capable microorganisms. The carbon is subsequently transferred to higher trophic levels. South of Svalbard, five geological mounds shaped by the formation of methane gas hydrates, have been recently located. Methane gas seeping activity has been observed on four of them, and flares were primarily concentrated at their summits. At three of these mounds, and along a distance gradient from their summit to their outskirt, we investigated the eukaryotic and prokaryotic biodiversity linked to 16S and 18S rDNA. Here we show that local methane seepage and other environmental conditions did affect the microbial community structure and composition. We could not demonstrate a community gradient from the summit to the edge of the mounds. Instead, a similar community structure in any methane-rich sediments could be retrieved at any location on these mounds. The oxidation of methane was largely driven by anaerobic methanotrophic Archaea-1 (ANME-1) and the communities also hosted high relative abundances of sulfate reducing bacterial groups although none demonstrated a clear co-occurrence with the predominance of ANME-1. Additional common taxa were observed and their abundances were likely benefiting from the end products of methane oxidation. Among these were sulfide-oxidizing Campilobacterota, organic matter degraders, such as Bathyarchaeota, Woesearchaeota, or thermoplasmatales marine benthic group D, and heterotrophic ciliates and Cercozoa.

Effectiveness of Fluorescent Viability Assays in Studies of Arctic Cold Seep Foraminifera

“…Similarly to Vestnesa Ridge, the benthic foraminiferal distribution pattern within the active GHP1 shows a greater variability along the analyzed transect compared to the transect along the inactive GHP5. The highest density of foraminifera is observed at the edge of GHP1, where white and gray bacterial mats are present, with a small difference in density toward the center of GHP1, and reaching zero individuals approximately at the top, where most of the methane flares are located (Serov et al, 2017;Carrier et al, 2020). The δ 13 C DIC value at the top of the active GHP reached −24.2 , which can be linked to methane-related microbial activity (Dessandier et al, 2019).…”

“…The active GHP1 is characterized by a greater percentage of recently dead (Rose Bengal stained) individuals, compared to living (CHG labeled) specimens, whereas in the inactive GHP5 pingo this ratio is reversed with more live than dead foraminifera. This difference between the active GHP1 and inactive GHP5 implies more unstable and variable environmental conditions at GHP1, potentially related to methane emissions, rather than general seasonal environmental changes (Carrier et al, 2020). On average, CHG labeling showed that approximately 40% of the benthic foraminifera in GHP1 and approximately 54% in GHP5 were alive at the time of collection.…”

“…The gas hydrate pingos (GHPs) are between 8 and 12 m high, with diameters between 280 and 450 m. Four of the five GHPs are presently active and show active methane seepage in the form of acoustically detected gas/bubble streams (i.e., acoustic flares) around the summits and one is in a "post-active stage" and presently inactive (Hong et al, 2017;Serov et al, 2017). Elevated concentrations of methane (mostly of thermogenic origin) have been detected in both sediments and bottom waters at GHP1, and gas hydrates were recovered in sediment cores (Hong et al, 2017;Carrier et al, 2020). The δ 13 C DIC values of pore water for the top of GHP1 (MC902) reached −24.2 (Dessandier et al, 2020).…”

“…The δ 13 C DIC value at the top of the active GHP reached −24.2 , which can be linked to methane-related microbial activity (Dessandier et al, 2019). The absence of foraminifera at the summit is thus most likely due to the combined effect of disturbance caused by gas bubbles passing though the sediment and geochemical constraints related to microbial activity (e.g., low oxygen or presence of hydrogen sulfide; Herguera et al, 2014;Carrier et al, 2020). The Shannon index shows that the suite of samples from GHP 5 has less variability compared to the samples from GHP1.…”

Microbiome Assessment of Global Oil Reservoirs Reveals Site-Specific Hydrocarbon Degradation Functional Profiles

“…Members of Nanoarchaeota phylum have already been found in hot springs in Yellowstone National Park (United States) under high temperature (~90oC) [64]. They are also associated to volcanoes rich in hydrocarbons [64], deep-sea hydrothermal vents and deep lakes [63][64][65][66][67][68][69][70][71][72][73]. Methermicoccus shengliensis is a methylotrophic methanogen.…”