Hung Chih-Hsin, Wu Hsung-Chi, Tseng Yi-Hsiung
Institute of Molecular Biology, National Chung Hsing University, Taiwan, Republic of China.
Biochem Biophys Res Commun. 2002 Feb 22;291(2):338-43. doi: 10.1006/bbrc.2002.6440.
(Phi)L7 is a lytic phage infecting the gram-negative Xanthomonas campestis pv. campestris, a plant pathogen. To study phage-host interaction, a (phi)L7-resistant mutant was isolated from strain Xc17 by mini-Tn5 transposition and designated CH7LR. CH7LR could not plate (phi)L7 in double-layered assay and formed turbid clearing zones when the cell lawn was dropped with a high titer of (phi)L7. Sequence analysis showed that the mutated gene is xanA coding for phosphoglucomutase/phosphomannomutase, required for the synthesis of lipopolysaccharide and exopolysaccharide (xanthan). The involvement of xanA was confirmed by isolating another mutant with interrupted xanA and complementing with the cloned wild-type gene. Nonmucoid mutants are still sensitive to (phi)L7, indicating that xanthan is not involved in (phi)L7 adsorption. Since the mutants still exhibited low efficiencies of phage adsorption, we predict, by analogy with the cases in other bacteriophages of gram-negative bacteria, that other outer membrane components such as a protein are required for the formation of a complex receptor.
（Phi）L7是一种裂解性噬菌体，可感染革兰氏阴性植物病原菌野油菜黄单胞菌野油菜致病变种。为了研究噬菌体与宿主的相互作用，通过mini-Tn5转座从Xc17菌株中分离出一株（phi）L7抗性突变体，并命名为CH7LR。在双层试验中，CH7LR不能使（phi）L7形成噬菌斑，当用高滴度的（phi）L7滴加细胞菌苔时，会形成浑浊的清亮区。序列分析表明，突变基因是xanA，其编码磷酸葡萄糖变位酶/磷酸甘露糖变位酶，这是脂多糖和胞外多糖（黄原胶）合成所必需的。通过分离另一个xanA中断的突变体并用克隆的野生型基因进行互补，证实了xanA的参与。非黏液型突变体对（phi）L7仍敏感，这表明黄原胶不参与（phi）L7的吸附。由于这些突变体仍表现出较低的噬菌体吸附效率，我们通过与其他革兰氏阴性菌噬菌体的情况进行类比预测，形成复合受体需要其他外膜成分，如一种蛋白质。
