A genomic island present along the bacterial chromosome of the Parachlamydiaceae UWE25, an obligate amoebal endosymbiont, encodes a potentially functional F-like conjugative DNA transfer system.
A genomic island present along the bacterial chromosome of the Parachlamydiaceae UWE25, an obligate amoebal endosymbiont, encodes a potentially functional F-like conjugative DNA transfer system.
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DOI：
10.1186/1471-2180-4-48
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发表时间：
2004-12-22
期刊：
影响因子：
4.2
通讯作者：
Roten CA
中科院分区：
文献类型：
--
作者：
Greub G;Collyn F;Guy L;Roten CA
Protochlamydia amoebophila UWE 25是一种与副衣原体相关的自由生活阿米巴内共生体，其基因组最近发表，为寻找基因组岛（GI）提供了机会。在残留累积G+C含量曲线上，观察到富含G+ C的19-kb区域。该序列是100 kb染色体区域的一部分，包含100个高度共定向的ORF，两侧是两个17 bp的同向重复序列。两个相同的gly-tRNA基因串联存在于该遗传元件的近端。编码转座酶和噬菌体相关蛋白的几个迁移基因位于该染色体区域内。因此，该地区基本上符合地理标志的标准。G+C的内容分析表明，几个模块组成的GI。令人惊讶的是，其中一个编码F样接合DNA转移所必需的所有基因（traF，traG，traH，traN，traU，traW和trbC），参与性菌毛收缩和交配对稳定，强烈表明，类似于其他F样操纵子，副衣原体tra单位致力于DNA转移。一个密切相关的这一tra单位的F-样tra操纵子参与接合转移证实了系统发育分析进行串联基因和基因顺序保守。这些分析和gly-tRNA分布在140个地理标志物表明变形菌起源的副衣原体tra单位。UWE 25染色体的GI编码潜在功能的F样DNA接合系统。这是披衣植物中假定的接合系统的第一个线索。接合最可能发生在自由生活的阿米巴原虫中，阿米巴原虫可能含有数百个紧密包装在空泡中的副衣原体细菌。这种接合系统可能参与内化细菌之间的DNA转移。由于该系统是不存在的衣原体科的测序基因组，我们假设它是收购后的分歧副衣原体科和衣原体科，当副衣原体相关的共生体是一个细胞内的细菌。这表明，这种异源DNA是从一个遗传上遥远的细菌共享一个变形虫空泡。由于副衣原体科是肺炎的新兴病原体，因此该GI可能参与致病性。在未来，接合系统可能被开发为衣原体的遗传工具。
The genome of Protochlamydia amoebophila UWE25, a Parachlamydia-related endosymbiont of free-living amoebae, was recently published, providing the opportunity to search for genomic islands (GIs). On the residual cumulative G+C content curve, a G+C-rich 19-kb region was observed. This sequence is part of a 100-kb chromosome region, containing 100 highly co-oriented ORFs, flanked by two 17-bp direct repeats. Two identical gly-tRNA genes in tandem are present at the proximal end of this genetic element. Several mobility genes encoding transposases and bacteriophage-related proteins are located within this chromosome region. Thus, this region largely fulfills the criteria of GIs. The G+C content analysis shows that several modules compose this GI. Surprisingly, one of them encodes all genes essential for F-like conjugative DNA transfer (traF, traG, traH, traN, traU, traW, and trbC), involved in sex pilus retraction and mating pair stabilization, strongly suggesting that, similarly to the other F-like operons, the parachlamydial tra unit is devoted to DNA transfer. A close relatedness of this tra unit to F-like tra operons involved in conjugative transfer is confirmed by phylogenetic analyses performed on concatenated genes and gene order conservation. These analyses and that of gly-tRNA distribution in 140 GIs suggest a proteobacterial origin of the parachlamydial tra unit. A GI of the UWE25 chromosome encodes a potentially functional F-like DNA conjugative system. This is the first hint of a putative conjugative system in chlamydiae. Conjugation most probably occurs within free-living amoebae, that may contain hundreds of Parachlamydia bacteria tightly packed in vacuoles. Such a conjugative system might be involved in DNA transfer between internalized bacteria. Since this system is absent from the sequenced genomes of Chlamydiaceae, we hypothesize that it was acquired after the divergence between Parachlamydiaceae and Chlamydiaceae, when the Parachlamydia-related symbiont was an intracellular bacteria. It suggests that this heterologous DNA was acquired from a phylogenetically-distant bacteria sharing an amoebal vacuole. Since Parachlamydiaceae are emerging agents of pneumonia, this GI might be involved in pathogenicity. In future, conjugative systems might be developed as genetic tools for Chlamydiales.
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