DNA sequence analysis of three Lactococcus lactis plasmids encoding phage resistance mechanisms
DNA sequence analysis of three Lactococcus lactis plasmids encoding phage resistance mechanisms
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DOI：
10.3168/jds.s0022-0302(01)74595-x
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发表时间：
2001-07-01
影响因子：
3.5
通讯作者：
Moineau, S
中科院分区：
文献类型：
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作者：
Boucher, I;Émond, É;Moineau, S
三种乳酸乳球菌质粒pSRQ 700、pSRQ 800和pSRQ 900分别编码先前描述的抗噬菌体抗性机制LlaDCHI、AbiK和AbiQ。由于这些质粒很可能被引入到用于生产商业发酵乳制品的工业乳酸乳球菌菌株中，因此测定并分析了它们的完整DNA序列。质粒pSRQ 700（7784 bp）、pSRQ 800（7858 bp）和pSRQ 900（10，836 bp）显示出相似的遗传结构，包括共同的乳球菌θ型复制子。在pSRQ 700上还发现了显示pMV 158滚环复制子家族特征的第二复制模块。三种质粒的θ复制区与两个额外的编码区相关，其中一个编码HsdS，即I型限制/修饰系统的特异性亚基。引入L. pSRQ 800和pSRQ 900的HsdS对噬菌体P008（936种）具有弱抗性。这些结果表明，两个HsdS亚基可以补充IL 1403中染色体编码的I型限制/修饰系统。发现参与噬菌体抗性系统LlaDCHI、AbiK和AbiQ的基因紧邻复制模块并位于复制模块的下游。在pSRQ 800和pSRQ 900中，在θ复制子的上游发现了转移起点和推定的酪氨酸重组酶。在pSRQ 700上也发现了编码重组蛋白的基因。最后，在pSRQ 900上发现了与细菌素产生相关的开放阅读框，但未检测到抗乳球菌活性。根据我们目前的知识，这三种质粒是安全的，适用于食品级应用。
The three Lactococcus lactis plasmids pSRQ700, pSRQ800, and pSRQ900 encode the previously described anti-phage resistance mechanisms LlaDCHI, AbiK, and AbiQ, respectively. Since these plasmids are likely to be introduced into industrial Lactococcus lactis strains used to manufacture commercial fermented dairy products, their complete DNA sequences were determined and analyzed. The plasmids pSRQ700 (7784 bp), pSRQ800 (7858 bp), and pSRQ900 (10,836 bp) showed a similar genetic organization including a common lactococcal theta-type replicon. A second replication module showing features of the pMV158 family of rolling circle replicons was also found on pSRQ700. The theta replication regions of the three plasmids were associated with two additional coding regions, one of which encodes for HsdS, the specificity subunit of the type I restriction/modification system. When introduced into L. lactis IL1403, the HsdS of pSRQ800 and pSRQ900 conferred a weak resistance against phage P008 (936 species). These results indicated that both HsdS subunits can complement the chromosomally encoded type I restriction/modification system in IL1403. The genes involved in the phage resistance systems LlaDCHI, AbiK, and AbiQ were found in close proximity to and downstream of the replication modules. In pSRQ800 and pSRQ900, transfer origins and putative tyrosine recombinases were found upstream of the theta replicons. Genes encoding recombination proteins were also found on pSRQ700. Finally, open reading frames associated with bacteriocin production were found on pSRQ900, but no anti-lactococcal activity was detected. Based on our current knowledge, these three plasmids are safe and suitable for food-grade applications.