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Stenow R, Robertson EK, Kourtchenko O, Whitehouse MJ, Pinder MIM, Benvenuto G, Töpel M, Godhe A, Ploug H. Resting cells of Skeletonema marinoi assimilate organic compounds and respire by dissimilatory nitrate reduction to ammonium in dark, anoxic conditions. Environ Microbiol 2024; 26:e16625. [PMID: 38653479 DOI: 10.1111/1462-2920.16625] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Accepted: 04/05/2024] [Indexed: 04/25/2024]
Abstract
Diatoms can survive long periods in dark, anoxic sediments by forming resting spores or resting cells. These have been considered dormant until recently when resting cells of Skeletonema marinoi were shown to assimilate nitrate and ammonium from the ambient environment in dark, anoxic conditions. Here, we show that resting cells of S. marinoi can also perform dissimilatory nitrate reduction to ammonium (DNRA), in dark, anoxic conditions. Transmission electron microscope analyses showed that chloroplasts were compacted, and few large mitochondria had visible cristae within resting cells. Using secondary ion mass spectrometry and isotope ratio mass spectrometry combined with stable isotopic tracers, we measured assimilatory and dissimilatory processes carried out by resting cells of S. marinoi under dark, anoxic conditions. Nitrate was both respired by DNRA and assimilated into biomass by resting cells. Cells assimilated nitrogen from urea and carbon from acetate, both of which are sources of dissolved organic matter produced in sediments. Carbon and nitrogen assimilation rates corresponded to turnover rates of cellular carbon and nitrogen content ranging between 469 and 10,000 years. Hence, diatom resting cells can sustain their cells in dark, anoxic sediments by slowly assimilating and respiring substrates from the ambient environment.
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Affiliation(s)
- Rickard Stenow
- Department of Marine Sciences, University of Gothenburg, Gothenburg, SE, Sweden
| | | | - Olga Kourtchenko
- Department of Marine Sciences, University of Gothenburg, Gothenburg, SE, Sweden
| | | | - Matthew I M Pinder
- Department of Marine Sciences, University of Gothenburg, Gothenburg, SE, Sweden
| | | | - Mats Töpel
- Department of Marine Sciences, University of Gothenburg, Gothenburg, SE, Sweden
- IVL-Swedish Environmental Research Institute, Gothenburg, SE, Sweden
| | - Anna Godhe
- Department of Marine Sciences, University of Gothenburg, Gothenburg, SE, Sweden
| | - Helle Ploug
- Department of Marine Sciences, University of Gothenburg, Gothenburg, SE, Sweden
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Stenow R, Olofsson M, Robertson EK, Kourtchenko O, Whitehouse MJ, Ploug H, Godhe A. Resting Stages of Skeletonema marinoi Assimilate Nitrogen From the Ambient Environment Under Dark, Anoxic Conditions. JOURNAL OF PHYCOLOGY 2020; 56:699-708. [PMID: 32012281 DOI: 10.1111/jpy.12975] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Accepted: 01/02/2020] [Indexed: 06/10/2023]
Abstract
The planktonic marine diatom Skeletonema marinoi forms resting stages, which can survive for decades buried in aphotic, anoxic sediments and resume growth when re-exposed to light, oxygen, and nutrients. The mechanisms by which they maintain cell viability during dormancy are poorly known. Here, we investigated cell-specific nitrogen (N) and carbon (C) assimilation and survival rate in resting stages of three S. marinoi strains. Resting stages were incubated with stable isotopes of dissolved inorganic N (DIN), in the form of 15 N-ammonium (NH4+ ) or -nitrate (NO3- ) and dissolved inorganic C (DIC) as 13 C-bicarbonate (HCO3- ) under dark and anoxic conditions for 2 months. Particulate C and N concentration remained close to the Redfield ratio (6.6) during the experiment, indicating viable diatoms. However, survival varied between <0.1% and 47.6% among the three different S. marinoi strains, and overall survival was higher when NO3- was available. One strain did not survive in the NH4+ treatment. Using secondary ion mass spectrometry (SIMS), we quantified assimilation of labeled DIC and DIN from the ambient environment within the resting stages. Dark fixation of DIC was insignificant across all strains. Significant assimilation of 15 N-NO3- and 15 N-NH4+ occurred in all S. marinoi strains at rates that would double the nitrogenous biomass over 77-380 years depending on strain and treatment. Hence, resting stages of S. marinoi assimilate N from the ambient environment at slow rates during darkness and anoxia. This activity may explain their well-documented long survival and swift resumption of vegetative growth after dormancy in dark and anoxic sediments.
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Affiliation(s)
- Rickard Stenow
- Department of Marine Sciences, University of Gothenburg, Box 461, SE 405 30, Gothenburg, Sweden
| | - Malin Olofsson
- Department of Marine Sciences, University of Gothenburg, Box 461, SE 405 30, Gothenburg, Sweden
| | - Elizabeth K Robertson
- Department of Marine Sciences, University of Gothenburg, Box 461, SE 405 30, Gothenburg, Sweden
| | - Olga Kourtchenko
- Department of Marine Sciences, University of Gothenburg, Box 461, SE 405 30, Gothenburg, Sweden
| | | | - Helle Ploug
- Department of Marine Sciences, University of Gothenburg, Box 461, SE 405 30, Gothenburg, Sweden
| | - Anna Godhe
- Department of Marine Sciences, University of Gothenburg, Box 461, SE 405 30, Gothenburg, Sweden
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Sandfeld T, Marzocchi U, Petro C, Schramm A, Risgaard-Petersen N. Electrogenic sulfide oxidation mediated by cable bacteria stimulates sulfate reduction in freshwater sediments. THE ISME JOURNAL 2020; 14:1233-1246. [PMID: 32042102 PMCID: PMC7174387 DOI: 10.1038/s41396-020-0607-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Revised: 01/27/2020] [Accepted: 01/30/2020] [Indexed: 11/08/2022]
Abstract
Cable bacteria are filamentous members of the Desulfobulbaceae family that oxidize sulfide with oxygen or nitrate by transferring electrons over centimeter distances in sediments. Recent studies show that freshwater sediments can support populations of cable bacteria at densities comparable to those found in marine environments. This is surprising since sulfide availability is presumably low in freshwater sediments due to sulfate limitation of sulfate reduction. Here we show that cable bacteria stimulate sulfate reduction in freshwater sediment through promotion of sulfate availability. Comparing experimental freshwater sediments with and without active cable bacteria, we observed a three- to tenfold increase in sulfate concentrations and a 4.5-fold increase in sulfate reduction rates when cable bacteria were present, while abundance and community composition of sulfate-reducing microorganisms (SRM) were unaffected. Correlation and ANCOVA analysis supported the hypothesis that the stimulation of sulfate reduction activity was due to relieve of the kinetic limitations of the SRM community through the elevated sulfate concentrations in sediments with cable bacteria activity. The elevated sulfate concentration was caused by cable bacteria-driven sulfide oxidation, by sulfate production from an indigenous sulfide pool, likely through cable bacteria-mediated dissolution and oxidation of iron sulfides, and by enhanced retention of sulfate, triggered by an electric field generated by the cable bacteria. Cable bacteria in freshwater sediments may thus be an integral component of a cryptic sulfur cycle and provide a mechanism for recycling of the scarce resource sulfate, stimulating sulfate reduction. It is possible that this stimulation has implication for methanogenesis and greenhouse gas emissions.
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Affiliation(s)
- Tobias Sandfeld
- Department of Bioscience, Section for Microbiology, Aarhus University, Aarhus, Denmark
- Center for Geomicrobiology, Aarhus University, Aarhus, Denmark
| | - Ugo Marzocchi
- Department of Bioscience, Section for Microbiology, Aarhus University, Aarhus, Denmark
- Center for Geomicrobiology, Aarhus University, Aarhus, Denmark
- Center for Electromicrobiology, Aarhus University, Aarhus, Denmark
- Department of Chemistry, Vrije Universiteit Brussel, Brussel, Belgium
| | - Caitlin Petro
- Department of Bioscience, Section for Microbiology, Aarhus University, Aarhus, Denmark
- Center for Geomicrobiology, Aarhus University, Aarhus, Denmark
- Center for Electromicrobiology, Aarhus University, Aarhus, Denmark
| | - Andreas Schramm
- Department of Bioscience, Section for Microbiology, Aarhus University, Aarhus, Denmark
- Center for Geomicrobiology, Aarhus University, Aarhus, Denmark
- Center for Electromicrobiology, Aarhus University, Aarhus, Denmark
| | - Nils Risgaard-Petersen
- Department of Bioscience, Section for Microbiology, Aarhus University, Aarhus, Denmark.
- Center for Geomicrobiology, Aarhus University, Aarhus, Denmark.
- Center for Electromicrobiology, Aarhus University, Aarhus, Denmark.
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