微生物令人吃驚的多樣性向科學(xué)家提出了一些棘手的問題,，如在任何一個給定環(huán)境中有多少種不同細(xì)菌共同生活在一起,？它們之間是什么關(guān)系？甚至還包括什么樣的東西才算是細(xì)菌這樣一個問題,。研究人員利用從海水中提取出的DNA對這些問題進(jìn)行了研究,。盡管數(shù)以千計的在基因組成上明顯不同的細(xì)菌共同生活在這些海水中，但它們多數(shù)都能歸入彼此關(guān)系非常相近的類別中,，這些類別與其他類別明顯不同,。預(yù)計執(zhí)行類似生態(tài)功能的生物也存在這種情況，在微生物世界中這可能就代表著一個物種,。
Fine-scale phylogenetic architecture of a complex bacterial community
Although molecular data have revealed the vast scope of microbial diversity, two fundamental questions remain unanswered even for well-defined natural microbial communities: how many bacterial types co-exist, and are such types naturally organized into phylogenetically discrete units of potential ecological significance? It has been argued that without such information, the environmental function, population biology and biogeography of microorganisms cannot be rigorously explored. Here we address these questions by comprehensive sampling of two large 16S ribosomal RNA clone libraries from a coastal bacterioplankton community. We show that compensation for artefacts generated by common library construction techniques reveals fine-scale patterns of community composition. At least 516 ribotypes (unique rRNA sequences) were detected in the sample and, by statistical extrapolation, at least 1,633 co-existing ribotypes in the sampled population. More than 50% of the ribotypes fall into discrete clusters containing less than 1% sequence divergence. This pattern cannot be accounted for by interoperon variation, indicating a large predominance of closely related taxa in this community. We propose that such microdiverse clusters arise by selective sweeps and persist because competitive mechanisms are too weak to purge diversity from within them.
