Wertz John E, Riley Margaret A
Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520, USA.
J Bacteriol. 2004 Mar;186(6):1598-605. doi: 10.1128/JB.186.6.1598-1605.2004.
The complete nucleotide sequences of two bacteriocin-encoding plasmids isolated from Hafnia alvei (pAlvA and pAlvB) were determined. Both plasmids resemble ColE1-type replicons and carry mobilization genes, as well as colicin-like bacteriocin operons. These bacteriocins appear to be chimeras consisting of translocation domains from Tol-dependent colicins, unique binding domains, and killing and immunity domains similar to those of the pore-forming colicin Ia. Just as is found for colicin Ia, these H. alvei bacteriocins (alveicins) lack lysis genes. The alveicins are unusually small at 408 and 358 amino acids for alveicin A and B, respectively, which would make alveicin B the smallest pore-forming bacteriocin yet discovered. The pattern of nucleotide substitution in the alveicins suggests that the dominant forces in the evolution of their killing domains and immunity genes are neutral mutation and random genetic drift rather than diversifying selection, which has been implicated in the evolution of other colicins. Five of six bacteriocinogenic isolates of H. alvei were found to carry plasmids identical to pAlvA. Comparisons of the levels of nucleotide divergence in five housekeeping genes to the levels of divergence in their respective plasmids led us to conclude that pAlvA is transferring laterally through the H. alvei population relatively rapidly.
测定了从蜂房哈夫尼亚菌中分离出的两种编码细菌素的质粒（pAlvA和pAlvB）的完整核苷酸序列。这两种质粒类似于ColE1型复制子，携带转移基因以及类大肠杆菌素细菌素操纵子。这些细菌素似乎是嵌合体，由来自Tol依赖性大肠杆菌素的转运结构域、独特的结合结构域以及与成孔大肠杆菌素Ia相似的杀伤和免疫结构域组成。正如在大肠杆菌素Ia中发现的那样，这些蜂房哈夫尼亚菌细菌素（蜂房菌素）缺乏裂解基因。蜂房菌素A和B分别异常小，仅含408和358个氨基酸，这将使蜂房菌素B成为迄今发现的最小的成孔细菌素。蜂房菌素中的核苷酸取代模式表明，其杀伤结构域和免疫基因进化中的主导力量是中性突变和随机遗传漂变，而非多样化选择，多样化选择与其他大肠杆菌素的进化有关。在蜂房哈夫尼亚菌的六个产细菌素分离株中，有五个被发现携带与pAlvA相同的质粒。通过比较五个管家基因的核苷酸差异水平与其各自质粒的差异水平，我们得出结论，pAlvA正在相对快速地在蜂房哈夫尼亚菌群体中横向转移。
