Comparative analyses of Legionella species to identify genetic features of strains causing Legionnaires' disease. Legionella micdadei strain:ATCC33218

In this study we show that the comparative analyses of 11 Legionella genomes belonging to five species revealed a highly different genome content with >60% of species-specific genes. These comprise a complete prophage in L. micdadei, the first identified in a Legionella genome and the findng that L. fallonii synthesizes cellulose and an active chitin deacetylase. Mobile elements are abundant. Many encode type IV secretion systems for conjugative transfer pointing to their iportance for adaptation. Although the Dot/Icm secretion system is conserved the core set of substrates is small, as only 24 out of >300 described Dot/Icm effector genes are present in all species. New eukaryotic motifs including thaumatin, synaptobrevin or clathrin/coatomer adaptine like domains were identified. Key factors such as proteins involved in oxygen binding, iron storage, host membrane transport and certain Dot/Icm substrates are specific features of disease related strains.

本研究通过对隶属于5个物种的11株军团菌（Legionella）基因组开展比较分析，发现其基因组组成差异显著，超过60%的基因为物种特异性基因。这些物种特异性基因包括：在米克戴德军团菌（L. micdadei）中发现的完整前噬菌体——这是首次在军团菌基因组中鉴定到的前噬菌体——以及洛氏军团菌（L. fallonii）可合成纤维素并产生活性几丁质脱乙酰酶的特性。移动遗传元件在该类群中十分丰富，其中多数编码用于接合转移的IV型分泌系统（Type IV Secretion System），提示其在菌株适应环境过程中发挥关键作用。尽管Dot/Icm分泌系统在各物种间保守存在，但其核心底物集合却十分有限：在已报道的300余个Dot/Icm效应蛋白基因中，仅有24个存在于所有受试物种中。本研究还鉴定到全新的真核生物基序，包括类索马甜（thaumatin）结构域、类突触小泡蛋白（synaptobrevin）结构域以及类网格蛋白/衣被蛋白接头蛋白（clathrin/coatomer adaptin）结构域。与致病相关菌株的特异性特征涵盖诸多关键因子，例如参与氧结合、铁储存、宿主膜转运的蛋白，以及部分Dot/Icm效应蛋白。