Eichner Meri J, Klawonn Isabell, Wilson Samuel T, Littmann Sten, Whitehouse Martin J, Church Matthew J, Kuypers Marcel Mm, Karl David M, Ploug Helle
Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden.
Department of Ecology, Environment and Plant Sciences, University of Stockholm, Stockholm, Sweden.
ISME J. 2017 Jun;11(6):1305-1317. doi: 10.1038/ismej.2017.15. Epub 2017 Apr 11.
Gradients of oxygen (O) and pH, as well as small-scale fluxes of carbon (C), nitrogen (N) and O were investigated under different partial pressures of carbon dioxide (pCO) in field-collected colonies of the marine dinitrogen (N)-fixing cyanobacterium Trichodesmium. Microsensor measurements indicated that cells within colonies experienced large fluctuations in O, pH and CO concentrations over a day-night cycle. O concentrations varied with light intensity and time of day, yet colonies exposed to light were supersaturated with O (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 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 fluxes nor C fixation by Trichodesmium were significantly influenced by short-term incubations under different pCO levels, whereas N fixation increased with increasing pCO. 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.
在从野外采集的海洋固氮蓝藻束毛藻的群体中，研究了不同二氧化碳分压（pCO₂）下的氧（O₂）和pH梯度，以及碳（C）、氮（N）和O₂的小规模通量。微传感器测量表明，群体内的细胞在昼夜循环中经历了O₂、pH和CO₂浓度的大幅波动。O₂浓度随光照强度和一天中的时间而变化，但在整个光照期，暴露于光照下的群体O₂过饱和（高达约200%），未检测到缺氧情况。光照和黑暗条件的交替导致pH水平平均变化0.5个单位（相当于15 nmol l⁻¹质子浓度）。使用二次离子质谱（SIMS；大几何尺寸SIMS和纳米级SIMS）对C和N同化进行的单细胞分析揭示了束毛藻单细胞和藻丝代谢活性的高度变异性，并表明C和N转移到了与群体相关的非光合细菌中。在不同pCO₂水平下短期培养，束毛藻的O₂通量和C固定均未受到显著影响，而N固定随pCO₂的增加而增加。在单细胞水平观察到的大范围代谢率可能反映了形成群体的微生物种群对高度可变微环境的响应。
