Evolutionary Changes in DnaA-Dependent Chromosomal Replication in Cyanobacteria
Evolutionary Changes in DnaA-Dependent Chromosomal Replication in Cyanobacteria
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DOI：
10.3389/fmicb.2020.00786
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发表时间：
2020-04
影响因子：
5.2
通讯作者：
R. Ohbayashi;S. Hirooka;Ryo Onuma;Y. Kanesaki;Yuu Hirose;Yusuke Kobayashi;T. Fujiwara;C. Furusawa-
中科院分区：
文献类型：
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作者：
R. Ohbayashi;S. Hirooka;Ryo Onuma;Y. Kanesaki;Yuu Hirose;Yusuke Kobayashi;T. Fujiwara;C. Furusawa-
环状细菌染色体的复制是以依赖于DNAA的方式在唯一起始点(ORIC)启动的，其中复制从ORIC到TER双向进行。大多数细菌的核苷酸组成在领先的和落后的DNA链之间不同。因此，染色体DNA序列通常表现出不对称的GC偏斜分布。此外，没有编码DNAA的基因组的自由生活的细菌是未知的。因此，依赖于DNAA的复制启动机制对大多数细菌可能是必不可少的。然而，大多数蓝藻基因组表现出不规则的GC偏斜分布。我们先前发现，细长聚球藻的染色体呈规则的GC偏斜分布，是以依赖于DNAA的方式复制的，而聚球藻的染色体则是以DNAA依赖的方式复制。PCC6803和发菜属(Nostoc sp.)PCC7120表现出不规则的GC歪斜特征，以DNAA独立的方式从多个来源复制。在这里，我们研究了蓝藻染色体复制机制的变化。我们发现，某些自由生活物种的基因组不编码DNAA，包括蓝藻aponinum PCC 10605和双胞藻sp.Nies-3708，从多个来源复制它们的染色体。聚球藻Pcc 7002，它与缺乏Dna A的自由生活物种以及编码Dna A但不依赖Dna A的集胞藻有密切的亲缘关系。PCC6803，具有DNAA。在聚球藻中。PCC7002，Dna A不是必需的，其染色体是以独立于Dna A的方式从唯一来源复制的。我们的结果还表明，在蓝藻进化过程中，DNAA依赖的丧失独立地发生了多次，并提出了一种可能性，即DNAA的丧失或DNAA依赖的丧失与倍性水平的增加有关。
Replication of the circular bacterial chromosome is initiated at a unique origin (oriC) in a DnaA-dependent manner in which replication proceeds bidirectionally from oriC to ter. The nucleotide compositions of most bacteria differ between the leading and lagging DNA strands. Thus, the chromosomal DNA sequence typically exhibits an asymmetric GC skew profile. Further, free-living bacteria without genomes encoding dnaA were unknown. Thus, a DnaA-oriC-dependent replication initiation mechanism may be essential for most bacteria. However, most cyanobacterial genomes exhibit irregular GC skew profiles. We previously found that the Synechococcus elongatus chromosome, which exhibits a regular GC skew profile, is replicated in a DnaA-oriC-dependent manner, whereas chromosomes of Synechocystis sp. PCC 6803 and Nostoc sp. PCC 7120, which exhibit an irregular GC skew profile, are replicated from multiple origins in a DnaA-independent manner. Here we investigate the variation in the mechanisms of cyanobacterial chromosome replication. We found that the genomes of certain free-living species do not encode dnaA and such species, including Cyanobacterium aponinum PCC 10605 and Geminocystis sp. NIES-3708, replicate their chromosomes from multiple origins. Synechococcus sp. PCC 7002, which is phylogenetically closely related to dnaA-lacking free-living species as well as to dnaA-encoding but DnaA-oriC-independent Synechocystis sp. PCC 6803, possesses dnaA. In Synechococcus sp. PCC 7002, dnaA was not essential and its chromosomes were replicated from a unique origin in a DnaA-oriC independent manner. Our results also suggest that loss of DnaA-oriC-dependency independently occurred multiple times during cyanobacterial evolution and raises a possibility that the loss of dnaA or loss of DnaA-oriC dependency correlated with an increase in ploidy level.