專題：Nature報導
小型浮遊藻對海洋生態系統有巨大貢獻，因為它們可通過光合作用來固定二氧化碳。對在夏季從北大西洋所取水樣進行的一項新的研究表明，浮遊藻類也消耗細菌，其細胞生物質的四分之一是通過「吃」浮遊菌獲得的。這一發現向認為浮遊藻類完全依靠無機營養物的假設提出了挑戰。
以前，專門化的原蟲被認為是細菌的主要捕食者，但儘管小型藻消耗細菌的速度比較慢，它們的數量卻非常大，以至於近表面海水中細菌消耗總量的40%至90%是由它們完成的。細菌消耗在一定程度上也許可解釋為什麼最小的藻類在海洋中佔據支配地位。（生物谷Bioon.com）
生物谷推薦原始出處：
Nature 455, 224-226 (11 September 2008) | doi:10.1038/nature07236
High bacterivory by the smallest phytoplankton in the North Atlantic Ocean
Mikhail V. Zubkov1 & Glen A. Tarran2
National Oceanography Centre, Southampton, Hampshire SO14 3ZH, UK
Plymouth Marine Laboratory, Plymouth, Devon PL1 3DH, UK
Planktonic algae <5 m in size are major fixers of inorganic carbon in the ocean1. They dominate phytoplankton biomass in post-bloom, stratified oceanic temperate waters2. Traditionally, large and small algae are viewed as having a critical growth dependence on inorganic nutrients, which the latter can better acquire at lower ambient concentrations owing to their higher surface area to volume ratios3, 4. Nonetheless, recent phosphate tracer experiments in the oligotrophic ocean5 have suggested that small algae obtain inorganic phosphate indirectly, possibly through feeding on bacterioplankton. There have been numerous microscopy-based studies of algae feeding mixotrophically6, 7 in the laboratory8, 9, 10 and field11, 12, 13,14, as well as mathematical modelling of the ecological importance of mixotrophy15. However, because of methodological limitations16 there has not been a direct comparison of obligate heterotrophic and mixotrophic bacterivory. Here we present direct evidence that small algae carry out 40–95% of the bacterivory in the euphotic layer of the temperate North Atlantic Ocean in summer. A similar range of 37–70% was determined in the surface waters of the tropical North-East Atlantic Ocean, suggesting the global significance of mixotrophy. This finding reveals that even the smallest algae have less dependence on dissolved inorganic nutrients than previously thought, obtaining a quarter of their biomass from bacterivory. This has important implications for how we perceive nutrient acquisition and limitation of carbon-fixing protists as well as control of bacterioplankton in the ocean.