Department of Ecology, University of Kaiserslautern, Kaiserslautern, Germany.
FEMS Microbiol Ecol. 2014 Mar;87(3):691-703. doi: 10.1111/1574-6941.12257. Epub 2013 Dec 5.
Phagotrophic protists are an important mortality factor of prokaryotes in most aquatic habitats. However, no study has assessed protistan grazing as loss factor of bacterial biomass across the stratification gradient of a temperate freshwater meromictic lake. Protistan grazing effect was quantified in the mixolimnion, the transition zone, and the sulfidic anoxic monimolimnion of Lake Alatsee (Germany). Grazing experiments were performed using prey analogues from the natural prokaryotic assemblage. Daily grazing effect declined from the mixolimnion to the monimolimnion. Heterotrophic flagellates were phagotrophically active in all three water horizons and the main grazers in the monimolimnion. Pigmented flagellates accounted for 70% of total grazing in the mixolimnion and ciliates only for a small fraction of grazing in each depth. Prokaryotic biomass removal peaked in the interface, but protistan impact on the respective prokaryotic abundance was low. Grazing in the anoxic monimolimnion was negligible, with prokaryotic turnover rate being only 0.4% of standing stock. Our results support the assumption that protistan predation in anoxic waters is lower than in oxygenated ones and identify the interface as a microhabitat that supports high grazer biomass, pinpointing the importance of purple sulfur bacteria as carbon source for the upper mixolimnion and the bottom monimolimnion.
噬菌原生动物是大多数水生栖息地中原核生物的重要死亡因素。然而，尚无研究评估过原生动物摄食作为温带淡水分层湖分层梯度中细菌生物量的损失因素。在阿特湖（德国）的混合层、过渡区和含硫缺氧的主分层区定量研究了原生动物摄食的作用。使用来自自然原核生物组合的猎物类似物进行了摄食实验。摄食作用从混合层到主分层区逐渐降低。异养鞭毛虫在所有三个水层中都具有噬菌活性，是主分层区的主要捕食者。有色鞭毛虫占混合层总摄食的 70%，而纤毛虫在每个深度的摄食中仅占很小一部分。在界面处，原核生物生物量的去除达到峰值，但原生动物对相应原核生物丰度的影响较低。缺氧主分层区的摄食可忽略不计，原核生物周转率仅为现存量的 0.4%。我们的研究结果支持这样的假设，即在缺氧水域中，原生动物捕食作用低于含氧水域，并确定界面为支持高食草生物量的微生境，突出了紫硫细菌作为上混合层和下主分层区碳源的重要性。
