School of Molecular Bioscience, University of Sydney, Sydney, Australia.
PLoS One. 2013 Jul 18;8(7):e69306. doi: 10.1371/journal.pone.0069306. Print 2013.
This paper covers eight Salmonella serogroups, that are defined by O antigens with related structures and gene clusters. They include the serovars that are now most frequently isolated. Serogroups A, B1, B2, C2-C3, D1, D2, D3 and E have O antigens that are distinguished by having galactose as first sugar, and not N-acetyl glucosamine or N-acetyl galactosamine as in the other 38 serogroups, and indeed in most Enterobacteriaceae. The gene clusters for these galactose-initiated appear to have entered S. enterica since its divergence from E. coli, but sequence comparisons show that much of the diversification occurred long before this. We conclude that the gene clusters must have entered S. enterica in a series of parallel events. The individual gene clusters are discussed, followed by analysis of the divergence for those genes shared by two or more gene clusters, and a putative phylogenic tree for the gene clusters is presented. This set of O antigens provides a rare case where it is possible to examine in detail the relationships of a significant number of O antigens. In contrast the more common pattern of O-antigen diversity within a species is for there to be only a few cases of strains having related gene clusters, suggesting that diversity arose through gain of individual O-antigen gene clusters by lateral gene transfer, and under these circumstances the evolution of the diversity is not accessible. This paper on the galactose-initiated set of gene clusters gives new insights into the origins of O-antigen diversity generally.
本文涵盖了八个沙门氏菌血清群，这些血清群由具有相关结构和基因簇的 O 抗原定义。它们包括现在最常分离到的血清型。血清群 A、B1、B2、C2-C3、D1、D2、D3 和 E 的 O 抗原的第一个糖是半乳糖，而不是其他 38 个血清群以及实际上大多数肠杆菌科中的 N-乙酰葡萄糖胺或 N-乙酰半乳糖胺。这些半乳糖起始的基因簇似乎是在 S. enterica 从大肠杆菌分化出来之后进入的，但序列比较表明，大部分多样化发生在很久以前。我们得出结论，这些基因簇必须在一系列平行事件中进入 S. enterica。我们讨论了各个基因簇，然后分析了两个或更多基因簇共享的基因的分化，并提出了基因簇的假设系统发育树。这组 O 抗原提供了一个罕见的案例，可以详细研究大量 O 抗原之间的关系。相比之下，在一个物种中 O 抗原多样性的更常见模式是只有少数菌株具有相关的基因簇，这表明多样性是通过水平基因转移获得单个 O 抗原基因簇而产生的，在这种情况下，多样性的进化是无法获得的。本文关于半乳糖起始基因簇的研究为 O 抗原多样性的起源提供了新的见解。
