Resolution of Prochlorococcus and Synechococcus ecotypes by using 16S-23S ribosomal DNA internal transcribed spacer sequences
Resolution of Prochlorococcus and Synechococcus ecotypes by using 16S-23S ribosomal DNA internal transcribed spacer sequences
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DOI：
10.1128/aem.68.3.1180-1191.2002
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发表时间：
2002-03-01
影响因子：
4.4
通讯作者：
Chisholm, SW
中科院分区：
文献类型：
--
作者：
Rocap, G;Distel, DL;Chisholm, SW
海洋蓝藻原绿球藻和聚球藻的培养分离株在其色素组成以及对光和营养物的生长反应方面差异很大，但其 16S 核糖体 DNA (rDNA) 序列显示出超过 96% 的同一性。为了更好地定义伴随其生理多样性的遗传变异，在来自全球的 32 个原绿球藻分离株和 25 个聚球藻分离株中确定了 16S-23S rDNA 内转录间隔区 (ITS) 区域的序列。检查的每个菌株都产生一个包含两个 tRNA 基因的 ITS 序列。在菌株之间观察到间隔区的长度和 G+C 含量的显着变化，特别是在原绿球藻菌株之间。预测 ITS 的二级结构模型，以便于系统发育分析的序列比对。先前观察到的原绿球藻分为两种生态型（因叶绿素含量不同而被称为高 B/A 型和低 B/A 型）的观点得到了支持，高 B/A 生态型又细分为四个遗传上不同的分支。基于 ITS 的系统发育将海洋 A 聚球藻群划分为 6 个进化枝，其中 3 个可能与特定表型（运动性、色适应和缺乏藻胆素）相关。进化枝内部和进化枝之间的序列分歧模式暗示了由适应性扫描驱动的进化模式，并且意味着每个进化枝代表了一个生态上独特的种群。此外，许多进化枝由从世界海洋不同区域分离出来的菌株组成，这意味着它们在地理上分布广泛。这些结果提供了进一步的证据，证明原绿球藻和聚球藻的自然种群由多种共存的生态型组成，它们在遗传上密切相关但在生理上不同，其相对丰度可能随着环境条件的变化而变化。
Cultured isolates of the marine cyanobacteria Prochlorococcus and Synechococcus vary widely in their pigment compositions and growth responses to light and nutrients, yet show greater than 96% identity in their 16S ribosomal DNA (rDNA) sequences. In order to better define the genetic variation that accompanies their physiological diversity, sequences for the 16S-23S rDNA internal transcribed spacer (ITS) region were determined in 32 Prochlorococcus isolates and 25 Synechococcus isolates from around the globe. Each strain examined yielded one ITS sequence that contained two tRNA genes. Dramatic variations in the length and G+C content of the spacer were observed among the strains, particularly among Prochlorococcus strains. Secondary-structure models of the ITS were predicted in order to facilitate alignment of the sequences for phylogenetic analyses. The previously observed division of Prochlorococcus into two ecotypes (called high and low-B/A after their differences in chlorophyll content) were supported, as was the subdivision of the high-B/A ecotype into four genetically distinct clades. ITS-based phylogenies partitioned marine cluster A Synechococcus into six clades, three of which can be associated with a particular phenotype (motility, chromatic adaptation, and lack of phycourobilin). The pattern of sequence divergence within and between clades is suggestive of a mode of evolution driven by adaptive sweeps and implies that each clade represents an ecologically distinct population. Furthermore, many of the clades consist of strains isolated from disparate regions of the world's oceans, implying that they are geographically widely distributed. These results provide further evidence that natural populations of Prochlorococcus and Synechococcus consist of multiple coexisting ecotypes, genetically closely related but physiologically distinct, which may vary in relative abundance with changing environmental conditions.