Chemical microenvironments and single-cell carbon and nitrogen uptake in field-collected colonies of Trichodesmium under different pCO2

• Published in: The ISME Journal Vol. 11; no. 6; pp. 1305 - 1317
• Main Authors: Eichner, Meri J, Klawonn, Isabell, Wilson, Samuel T, Littmann, Sten, Whitehouse, Martin J, Church, Matthew J, Kuypers, Marcel MM, Karl, David M, Ploug, Helle
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.06.2017; Nature Publishing Group
• Subjects: 101/58; 14/63; 631/326/171/1878; 704/158/2165; 704/158/2466; 704/158/855; Anoxia; Assimilation; Bacteria; Biomedical and Life Sciences; Carbon; Carbon dioxide; Climate Research; Colonies; Ecology; Ecosystems and species history; Ekologi; Ekosystem och arthistoria; Evolutionary Biology; Fixation; Fluxes; Geosciences, Multidisciplinary; Klimatforskning; Life Sciences; Light intensity; Light levels; Luminous intensity; Mass spectrometry; Mass spectroscopy; Metabolism; Microbial Ecology; Microbial Genetics and Genomics; Microbiology; Microenvironments; Microorganisms; Multidisciplinär geovetenskap; Night; Nitrogen; Nitrogen fixation; Original; original-article; Photosynthesis; Populations; Secondary ion mass spectrometry; Time of use; Trichomes
• ISSN: 1751-7362; 1751-7370; 1751-7370
• DOI: 10.1038/ismej.2017.15

Gradients of oxygen (O 2 ) and pH, as well as small-scale fluxes of carbon (C), nitrogen (N) and O 2 were investigated under different partial pressures of carbon dioxide ( p CO 2 ) in field-collected colonies of the marine dinitrogen (N 2 )-fixing cyanobacterium Trichodesmium . Microsensor measurements indicated that cells within colonies experienced large fluctuations in O 2 , pH and CO 2 concentrations over a day–night cycle. O 2 concentrations varied with light intensity and time of day, yet colonies exposed to light were supersaturated with O 2 (up to ~200%) throughout the light period and anoxia was not detected. Alternating between light and dark conditions caused a variation in pH levels by on average 0.5 units (equivalent to 15 nmol l −1 proton concentration). Single-cell analyses of C and N assimilation using secondary ion mass spectrometry (SIMS; large geometry SIMS and nanoscale SIMS) revealed high variability in metabolic activity of single cells and trichomes of Trichodesmium, and indicated transfer of C and N to colony-associated non-photosynthetic bacteria. Neither O 2 fluxes nor C fixation by Trichodesmium were significantly influenced by short-term incubations under different p CO 2 levels, whereas N 2 fixation increased with increasing p CO 2 . The large range of metabolic rates observed at the single-cell level may reflect a response by colony-forming microbial populations to highly variable microenvironments.