Department of Biological Oceanography, Leibniz Institute for Baltic Sea Research Warnemünde, Rostock, Germany.
PLoS One. 2012;7(7):e41970. doi: 10.1371/journal.pone.0041970. Epub 2012 Jul 30.
Our knowledge of the phylogeny and diversity of aquatic protists is rapidly increasing due to molecular surveys and next-generation sequencing approaches. This has led to a considerable discrepancy between the taxa known from cultures and those known from environmental 18S rRNA gene sequences. Hence, it is generally difficult to assign ecological functions to new taxa detected by culture-independent molecular approaches.
METHODOLOGY/PRINCIPAL FINDINGS: A combination of unamended dark incubations and 18S rRNA sequencing was chosen to link molecular diversity data of uncultured protists with heterotrophic, presumably bacterivorous, growth. The incubations, conducted with Baltic Sea brackish water, resulted in a consistent shift from a protistan community dominated by phototrophs to one in which heterotrophs predominated. This was determined on the basis of cell abundance and 18S rRNA sequences derived from fingerprint analysis and clone libraries. The bulk of enriched phylotypes after incubation were related to hitherto uncultured marine taxa within chrysophytes, ochrophytes, choanoflagellates, cercozoans, and picobiliphytes, mostly represented in recently established or here defined environmental clades. Their growth in the dark, together with coinciding results from studies with a similar objective, provides evidence that these uncultured taxa represent heterotrophic or mixotrophic species.
CONCLUSIONS/SIGNIFICANCE: These findings shed some light into the trophic role of diverse uncultured protists especially within functionally heterogeneous groups (e.g., chrysophytes, ochrophytes) and groups that appear to be puzzling with regard to their nutrition (picobiliphytes). Additionally, our results indicate that the heterotrophic flagellate community in the southwestern Baltic Sea is dominated by species of marine origin. The combination of unamended incubations with molecular diversity analysis is thus confirmed as a promising approach to explore the trophic mode of environmentally relevant protist taxa for which only sequence data are currently available.
由于分子调查和下一代测序方法的应用，我们对水生原生生物的系统发育和多样性的认识正在迅速增加。这导致了从培养物中已知的分类单元与从环境 18S rRNA 基因序列中已知的分类单元之间存在相当大的差异。因此，通常很难将通过非培养分子方法检测到的新分类单元的生态功能分配给它们。
方法/主要发现：选择未经修饰的暗培养和 18S rRNA 测序相结合，将未培养原生生物的分子多样性数据与异养（可能是细菌食性）生长联系起来。这些培养实验是在波罗的海咸水中进行的，结果导致了一个从以光合生物为主的原生生物群落向以异养生物为主的原生生物群落的一致转变。这是基于细胞丰度和从指纹分析和克隆文库中获得的 18S rRNA 序列来确定的。培养后大量富集的类群与以前未培养的海洋分类群有关，这些分类群属于金藻、黄藻、领鞭毛生物、有孔虫和蓝藻门，主要代表了最近建立的或在此定义的环境分支。它们在黑暗中的生长，以及具有类似目标的研究的结果，提供了证据表明这些未培养的分类群代表异养或混养物种。
结论/意义：这些发现为不同的未培养原生生物的营养作用提供了一些线索，特别是在功能上具有异质性的群体（如金藻门、黄藻门）和那些在营养方面似乎令人困惑的群体（如蓝藻门）。此外，我们的结果表明，波罗的海南部的异养鞭毛虫群落主要由海洋来源的物种组成。因此，未经修饰的培养与分子多样性分析相结合，被证实是一种很有前途的方法，可以探索目前只有序列数据的与环境相关的原生生物分类单元的营养模式。
