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Anaerobic oxidation of methane (AOM) is hypothesized to occur through reverse hydrogenotrophic methanogenesis in marine sediments because sulfate reducers pull hydrogen concentrations so low that reverse hydrogenotrophic methanogenesis is exergonic. If true, hydrogenotrophic methanogenesis can theoretically co-occur with sulfate reduction if the organic matter is so labile that fermenters produce more hydrogen than sulfate reducers can consume, causing hydrogen concentrations to rise. Finding accumulation of biologically-produced methane in sulfate-containing organic-rich sediments would therefore support the theory that AOM occurs through reverse hydrogenotrophic methanogenesis since it would signal the absence of net AOM in the presence of sulfate. Methods16S rRNA gene libraries were compared to geochemistry and incubations in high depth-resolution sediment cores collected from organic-rich Cape Lookout Bight, North Carolina. ResultsWe found that methane began to accumulate while sulfate is still abundant (6–8 mM). Methane-cycling archaeaANME-1,Methanosarciniales, andMethanomicrobialesalso increased at these depths. Incubations showed that methane production in the upper 16 cm in sulfate-rich sediments was biotic since it could be inhibited by 2-bromoethanosulfonoic acid (BES). DiscussionWe conclude that methanogens mediate biological methane production in these organic-rich sediments at sulfate concentrations that inhibit methanogenesis in sediments with less labile organic matter, and that methane accumulation and growth of methanogens can occur under these conditions as well. Our data supports the theory that H2concentrations, rather than the co-occurrence of sulfate and methane, control whether methanogenesis or AOM via reverse hydrogenotrophic methanogenesis occurs. We hypothesize that the high amount of labile organic matter at this site prevents AOM, allowing methane accumulation when sulfate is low but still present in mM concentrations.
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Modulation of Saprolegnia parasitica growth with copper and ionophores
Abstract Saprolegnia parasiticais an oomycete pathogen responsible for saprolegniasis diseases that result in large production losses in the catfish and salmon aquaculture industry. The use of copper sulfate as an anti-Saprolegnia treatment has been reported as an alternative to malachite green, formaldehyde and hydrogen peroxide treatment methods. The current study investigates a new strategy to inhibitSaprolegnia parasiticagrowth by combining copper and ionophores at low levels. The chemical agents tetraethylthiuram disulfide (TDD), ciclopirox olamine (CLP), 2-mercaptopyridine N-oxide (MPO), 5-chloro-8-hydroxy-7-iodoquinoline (CHI), 5,7-dichloro-8-hydroxyquinoline (DHQ) and 8-Quinolinol (8QN) were identified to inhibitS. parasiticagrowth in a copper-dependent manner. At concentrations below the lethal dose of individual ionophore, increasing copper concentrations resulted in synergeticS. parasiticagrowth inhibition. The addition of the exogenous copper chelator bathocuproine sulfate (BCS), reversed the inhibition ofS. parasiticagrowth by TDD, CLP, MPO, and 8QN but not CHI and DHQ. Our data demonstrates that ionophores, in combination with low levels of copper, can effectively limitS. parasiticagrowth both in a liquid and solid support growth environment. Investigations into the underlying mechanism of Cu-ionophore toxicity are discussed.
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- Award ID(s):
- 2150510
- PAR ID:
- 10628321
- Publisher / Repository:
- bioRxiv
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Posted Content:
- https://doi.org/10.1101/2024.06.17.599375
