Duplessis M, Moineau S
Département de Biochimie et de Microbiologie, Faculté des Sciences et de Génie, Université Laval, Québec, Canada, G1K 7P4.
Mol Microbiol. 2001 Jul;41(2):325-36. doi: 10.1046/j.1365-2958.2001.02521.x.
Phage-host interactions remain poorly understood in lactic acid bacteria and essentially in all Gram-positive bacteria. The aim of this study was to identify the phage genetic determinant (anti-receptor) involved in the recognition of Streptococcus thermophilus hosts. The complete genomic sequence of the lytic S. thermophilus phage DT1 was determined previously, and bioinformatic analysis indicated that orf18 might be the anti-receptor gene. The orf18 of six additional S. thermophilus phages was determined (DT2, DT4, MD1, MD2, MD4 and Q5) and compared with the orf18 of DT1. The deduced ORF18 was divided into three domains. The first domain, which contains the N-terminal part of the protein, was conserved in all seven phages. The second domain was detected in only two phages and flanked by a motif called collagen-like repeats. The second domain also contained a variable region (VR1). All seven phages had a third domain that consisted of the C-terminal section of the protein as well as another variable region (VR2). Chimeric DT1 phages were constructed by recombination; a portion of its orf18 was replaced by the corresponding section in orf18 of the phage MD4. All DT1 chimeric phages acquired the host range of phage MD4. Analysis of the orf18 in the chimeric phages revealed that host specificity in phages DT1 and MD4 resulted from VR2. This is the first report on the identification and characterization of a phage gene involved in the host recognition process of Gram-positive bacteria.
噬菌体与宿主之间的相互作用在乳酸菌中，尤其是在所有革兰氏阳性菌中，仍未得到充分了解。本研究的目的是鉴定参与嗜热链球菌宿主识别的噬菌体遗传决定因素（抗受体）。此前已测定了裂解性嗜热链球菌噬菌体DT1的完整基因组序列，生物信息学分析表明orf18可能是抗受体基因。测定了另外六种嗜热链球菌噬菌体（DT2、DT4、MD1、MD2、MD4和Q5）的orf18，并与DT1的orf18进行了比较。推导的ORF18分为三个结构域。第一个结构域包含蛋白质的N端部分，在所有七种噬菌体中都是保守的。第二个结构域仅在两种噬菌体中检测到，两侧有一个称为胶原样重复序列的基序。第二个结构域还包含一个可变区（VR1）。所有七种噬菌体都有第三个结构域，由蛋白质的C端部分以及另一个可变区（VR2）组成。通过重组构建了嵌合DT1噬菌体；其orf18的一部分被噬菌体MD4的orf18中的相应部分取代。所有DT1嵌合噬菌体都获得了噬菌体MD4的宿主范围。对嵌合噬菌体中orf18的分析表明，噬菌体DT1和MD4中的宿主特异性是由VR2导致的。这是关于革兰氏阳性菌宿主识别过程中涉及的噬菌体基因的鉴定和表征的第一份报告。
