Since the delineation of 12 bacterial phyla by comparative phylogenetic analyses of 16S ribosomal RNA in 1987 knowledge of microbial diversity has expanded dramatically owing to the sequencing of ribosomal RNA genes cloned from environmental DNA. Currently, only 26 of the approximately 52 identifiable major lineages, or phyla, within the domain Bacteria have cultivated representatives. Evidence from field studies indicates that many of the uncultivated phyla are found in diverse habitats, and some are extraordinarily abundant. In some important environments, including seawater, freshwater, and soil, many biologically and geochemically important organisms are at best only remotely related to any strain that has been characterized by phenotype or by genome sequencing. Genome sequence information that would allow ribosomal RNA gene trees to be related to broader patterns in microbial genome evolution is scant, and therefore microbial diversity remains largely unexplored territory.

中文翻译：

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未经培养的微生物居多。

自从1987年通过对16S核糖体RNA的系统进化分析比较确定12种细菌菌门以来，由于从环境DNA克隆的核糖体RNA基因的测序，微生物多样性的知识得到了极大的扩展。目前，细菌域内大约52个可识别的主要谱系或门中只有26个培养了代表。野外研究的证据表明，许多未栽培的门都在不同的生境中发现，其中有些非常丰富。在一些重要的环境中，包括海水，淡水和土壤，许多生物学和地球化学上重要的生物充其量仅与已通过表型或基因组测序表征的任何菌株远距离相关。