Laboratoire Microorganismes: Génome et Environnement, UMR CNRS 6023, Clermont Université, Université Blaise Pascal, BP 80026, 63171, Aubiere Cedex, France,
Microb Ecol. 2013 Nov;66(4):906-16. doi: 10.1007/s00248-013-0289-x. Epub 2013 Sep 24.
The effects of viral lysis and heterotrophic nanoflagellate grazing (top down forces) on prokaryotic mortality and their subsequent impact on their metabolism were estimated in the upper euphotic and deeper aphotic depth of 11 freshwater lakes located in the French Massif Central. The standing stocks of viruses (VA) and heterotrophic nanoflagellate (HNF) varied significantly (p < 0.05) with sampled depth. VA was substantially (twofold on an average) and significantly higher (p < 0.03) at the aphotic compared to euphotic depth, whereas the reverse was true (p < 0.02) for HNF. Among the prokaryote subgroup, high nucleic acid content prokaryotes explained for significant variability in the total VA and served as principle host target for viral proliferation. Like standing stocks, flagellate grazing and viral infection rates also followed similar patterns. In the investigated lakes, the mechanism for regulating prokaryotic production varied with sampled depth from grazing control in the euphotic to control due to viral lysis in the aphotic. We also tested the hypothesis of top down control on prokaryotic growth efficiency (PGE, which we used as an index of prokaryotic physiological and energetic status at the community level) at both depths. Overall, among the studied lakes, PGE varied widely (4-51 %) with significantly (p < 0.05) lower values in the aphotic (mean = 18 ± 4 %) than euphotic depth (mean = 32 ± 9 %). Contrasting observations on the top down control of PGE between sampled depths were observed. The presence of grazers was found to stimulate PGE at the euphotic, whereas viruses through their lytic infection had a strong negative impact on PGE at the aphotic depth. Such observed differences in PGE and the mechanism controlling prokaryotic production with depth could eventually have strong implication on carbon and nutrient flux patterns in the studied lakes.
在法国中央高原的 11 个淡水湖中，我们估计了病毒裂解和异养微型鞭毛虫摄食（自上而下的力量）对原核生物死亡率的影响，以及它们对其代谢的后续影响。病毒（VA）和异养微型鞭毛虫（HNF）的存量随采样深度显著变化（p < 0.05）。VA 在暗区明显（平均增加两倍）且显著高于（p < 0.03）光区，而 HNF 则相反（p < 0.02）。在原核生物亚群中，高核酸含量原核生物解释了 VA 总变异的显著变异性，并作为病毒增殖的主要宿主靶标。与存量一样，鞭毛虫摄食和病毒感染率也遵循类似的模式。在所研究的湖泊中，调节原核生物生产力的机制随采样深度而变化，从光区的摄食控制到暗区的病毒裂解控制。我们还在两个深度测试了对原核生物生长效率（PGE，我们将其用作社区水平原核生物生理和能量状态的指标）进行自上而下控制的假设。总的来说，在所研究的湖泊中，PGE 变化很大（4-51%），暗区（平均 18%±4%）显著低于光区（平均 32%±9%）（p < 0.05）。在采样深度上，对 PGE 的自上而下控制观察到相反的结果。在光区，捕食者的存在被发现刺激了 PGE，而在暗区，病毒通过裂解感染对 PGE 产生了强烈的负面影响。这种观察到的 PGE 和控制原核生物生产力的机制随深度的差异最终可能对研究湖泊中的碳和养分通量模式产生强烈影响。
