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Updated: May 28, 2026

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O
Published on: October 7, 2020
Carbon and nitrogen assimilation in deep subseafloor microbial cells
Yuki Morono1, Takeshi Terada, Manabu Nishizawa
1Kochi Institute for Core Sample Research, Japan Agency for Earth-Marine Science and Technology (JAMSTEC), Nankoku, Kochi 783-8502, Japan. morono@jamstec.go.jp
Deep subseafloor microbes are metabolically active, utilizing glucose, pyruvate, and amino acids for growth. Their recovery in vitro is primarily limited by energy availability, not carbon or nitrogen compounds.
Area of Science:
- Microbiology
- Geochemistry
- Oceanography
Background:
- Subseafloor sediments host vast microbial populations under extreme nutrient and energy limitation.
- The metabolic capabilities and energy demands of these deep, ancient microbes are largely unknown.
Purpose of the Study:
- To investigate carbon and nitrogen assimilation in individual microbial cells from deep subseafloor sediments.
- To determine the metabolic activity and growth potential of microbes in ancient marine environments.
Main Methods:
- Stable isotope tracer incubation using (13)C and (15)N labeled substrates.
- Nanometer-scale secondary ion mass spectrometry (NanoSIMS) for analyzing individual cell assimilation.
- Incubation of lower Pleistocene sediments from the northwestern Pacific.
Main Results:
- Microbial growth and significant assimilation of (13)C/(15)N observed with glucose, pyruvate, and amino acids (∼76% of cells).
- Acetate and bicarbonate were assimilated but did not support growth; methane showed no assimilation or growth.
- Nitrogen assimilation from ammonium was preferential, suggesting a higher demand for nitrogen for in vitro recovery.
Conclusions:
- Deep subseafloor microbes retain metabolic activity and growth potential.
- Microbial growth in these environments is primarily energy-limited, rather than limited by carbon or nitrogen availability.
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