Muñoz R, García E, López R
Departamento de Microbiología Molecular, CSIC, Madrid, Spain.
J Mol Evol. 1998 Apr;46(4):432-6. doi: 10.1007/pl00006322.
Capsular polysaccharides are important virulence factors both in Gram-positive and Gram-negative bacteria. A similar cluster organization of the genes involved in the synthesis of bacterial exopolysaccharides has been postulated in both cases, suggesting that these clusters evolved by module assembly. Horizontal gene transfer has been postulated to explain the polymorphism found in these cellular polymers. The cap1 K and cap3A genes coding for the pneumococcal type 1 and type 3 UDP-glucose dehydrogenases, respectively, have been compared with other UDP-sugar dehydrogenases. We have observed that the evolutionary distance between Cap1K and Cap3A is approximately equal to that found between Cap1K (or Cap3A) and other UDP-GlcDH of families evolutionarily distant like KfiD, the dehydrogenase from Escherichia coli K5. On the basis of comparisons of G + C content, patterns of synonymous and nonsynonymous substitutions, dinucleotide frequencies, and codon usage bias, we conclude that the kfiD gene has been introduced into E. coli from an exogenous source, probably from a streptococcal species.
荚膜多糖在革兰氏阳性菌和革兰氏阴性菌中都是重要的毒力因子。在这两种情况下，都假定参与细菌胞外多糖合成的基因具有相似的簇组织，这表明这些簇是通过模块组装进化而来的。有人提出水平基因转移来解释这些细胞聚合物中发现的多态性。分别编码肺炎球菌1型和3型UDP - 葡萄糖脱氢酶的cap1K和cap3A基因已与其他UDP - 糖脱氢酶进行了比较。我们观察到，Cap1K和Cap3A之间的进化距离大约等于Cap1K（或Cap3A）与其他进化距离较远的家族的UDP - GlcDH（如来自大肠杆菌K5的脱氢酶KfiD）之间的进化距离。基于对G + C含量、同义替换和非同义替换模式、二核苷酸频率以及密码子使用偏好的比较，我们得出结论，kfiD基因是从外源引入大肠杆菌的，可能来自链球菌物种。
