In ecology, the enumeration of living aquatic unicellular protists is a century-old complicated task. The organisms are small, perhaps motile, and if they are non-motile their vitality is hard to gauge. A respectable technique still in use today is the Serial Dilution Culture-Most Probable Number (MPN) assay that determines the total viable phytoplankton concentration from the highest sample dilutions that exhibit chlorophyll-fluorescence after incubation. However, 99% of extant phytoplankton species have not been shown to grow in MPN tubes (false-negatives) and in ballast water applications, 10-50 µm species can be outcompeted by <10 µm autotrophs in abundance, biomass, and chlorophyll-fluorescence (false-positives). In addition, it is shown that after microscopic identification, contrary to established practice, the concentration of individual species or species-groups (10-50 µm) cannot be derived from standard MPN tables. Examples of a corrected derivation are given for simple (2-3 species) assemblages, but this correction becomes increasingly difficult in more complex mixtures. The MPN assay should not be used as a quantitative method in ecological studies or in applications such as ballast water testing.

中文翻译：

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用于估计压载水中浮游植物浓度的连续稀释培养 - 最可能的数量测定：评论和改进


在生态学中，活体水生单细胞原生生物的计数是一项长达一个世纪的复杂任务。这些生物体很小，可能是可以运动的，如果它们不运动，它们的活力就很难衡量。今天仍在使用的一种受人尊敬的技术是连续稀释培养-最可能数 （MPN） 测定，它从孵育后表现出叶绿素荧光的最高样品稀释度中确定活浮游植物的总活体浓度。然而，99% 的现存浮游植物物种尚未显示在 MPN 管中生长（假阴性），并且在压载水中应用，10-50 μm 物种在丰度、生物量和叶绿素荧光（假阳性）方面可以被 <10 μm 自养生物竞争。此外，结果表明，在显微镜鉴定后，与既定做法相反，单个物种或物种组 （10-50 μm） 的浓度不能从标准 MPN 表中得出。对于简单（2-3 种）组合，给出了校正推导的示例，但在更复杂的混合物中，这种校正变得越来越困难。MPN 分析不应用作生态研究或压载水测试等应用中的定量方法。