Methane Carbon Supports Aquatic Food Webs to the Fish Level

Abstract

Large amounts of the greenhouse gas methane (CH4) are produced by anaerobic mineralization of organic matter in lakes. In spite of extensive freshwater CH4 emissions, most of the CH4 is typically oxidized by methane oxidizing bacteria (MOB) before it can reach the lake surface and be emitted to the atmosphere. In turn, it has been shown that the CH4-derived biomass of MOB can provide the energy and carbon for zooplankton and macroinvertebrates. In this study, we demonstrate the presence of specific fatty acids synthesized by MOB in fish tissues having low carbon stable isotope ratios. Fish species, zooplankton, macroinvertebrates and the water hyacinth Eichhornia crassipes were collected from a shallow lake in Brazil and analyzed for fatty acids (FA) and carbon stable isotope ratios (δ13C). The fatty acids 16∶1ω8c, 16∶1ω8t, 16∶1ω6c, 16∶1ω5t, 18∶1ω8c and 18∶1ω8t were used as signature for MOB. The δ13C ratios varied from −27.7‰ to −42.0‰ and the contribution of MOB FA ranged from 0.05% to 0.84% of total FA. Organisms with higher total content of MOB FAs presented lower δ13C values (i.e. they were more depleted in 13C), while organisms with lower content of MOB signature FAs showed higher δ13C values. An UPGMA cluster analysis was carried out to distinguish grouping of organisms in relation to their MOB FA contents. This combination of stable isotope and fatty acid tracers provides new evidence that assimilation of methane-derived carbon can be an important carbon source for the whole aquatic food web, up to the fish level.

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“…Notably, our results reflect exclusively the incorporation of dissolved inorganic carbon as CO 2 , and not chemosynthesis based on other C1 compounds, an important pathway in particular considering methanotrophic bacteria (Bastviken et al 2003a;Ravinet et al 2010;Sanseverino et al 2012). This indicates that the results obtained with the method provided in this study are a conservative estimation of DCF.…”

“…The quantitative role of bacterial chemoautotrophic activity and the importance of DCF in lake sediments are still unknown, yet may constitute a significant pathway close to redox boundaries and importance as an energy source for the food web (Rawcliffe et al 2010;Ravinet et al 2010, Sanseverino et al 2012. One practical, simple approach is to trace the incorporation of 14 C labeled inorganic carbon in sediment slurry incubations.…”

Freshwater in flux

“…Indeed, the 13 C signature of spiders near a lake in Germany undergoes a large seasonal shift that coincides with the hatching of lake chironomids 3 . And fish in a Brazilian lake have been shown to be depleted in 13 C, and to contain the same suite of fatty acids found in methaneconsuming bacteria 4 . The notion that lake methane partially supports higher organisms in surrounding terrestrial environments fundamentally changes our understanding of how aquatic food webs work.…”

Phylogenetic Study of Methanol Oxidizers from Chilika-Lake Sediments Using Genomic and Metagenomic Approaches

“…For PCR amplification, final genomic DNA concentration was adjusted to 50 ng/ll. 16S rRNA gene was partially amplified using primers pA (5 0 -AGAGTTTGATCCTGGCTCAG3 0 ; E. coli position [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] and pH (5 0 -AAGGAGGTGATCCAGCCGCA3 0 ; E. coli position 1525-1544) [31]. Amplification was carried out on a thermal cycler (Biorad PTC0220) in 100 ll volume by mixing 50-90 ng template DNA with polymerase reaction buffer (109); 100 lM (each) dATP, dCTP, dTTP and dGTP; primers pA and pH (20 ng each) and 1.0 U Taq polymerase using following conditions: initial denaturation at 94°C for 1.5 min; 35 cycles at 95°C for 1.0 min, 55°C for 1.0 min, 72°C for 1.0 min; and final extension at 72°C for 5 min.…”

“…Alkalitolerant halophilic and type I alkaliphilic halotolerant methanotrophs utilize methane and methanol, to oxidize ammonium ions, and to transform various organic compounds even at 12 % salinity and 5-11 pH [15]. Recent investigations reported methanol utilizing methylotrophs from salty water-bodies having impact on global warming and bioremediation of pollution by methanol and other C 1 compounds [15][16][17][18]. Microscopic and enzymatic evidence of the reducing sediments at hypersaline seeps in the abyssal Gulf of Mexico supported the hypothesis that methylotrophs capable of using reduced C 1 compounds as their carbon and energy sources occur as intracellular symbionts of the seep mussel and other benthic invertebrates resembling hydrothermal vent community assemblages [12].…”