Department of Biology, University of Crete, P.O. Box 2208, 71409 Heraklion, Greece.
Infect Genet Evol. 2011 Aug;11(6):1352-60. doi: 10.1016/j.meegid.2011.04.029. Epub 2011 May 11.
A diversity of molecular translocation mechanisms, including various secretion systems, has been elaborated in host-bacterial interactions. The newly described type VI secretion system (T6SS) appears to be involved in bacterial pathogenesis by acting as a nano-syringe, contributing in translocation of several effector-proteins into the eukaryotic host cell cytoplasm. Recent evidences revealed the involvement of T6SS machinery in inter-bacterial interactions. Several Pseudomonas species are found to harbour multiple and well organised T6SS loci, however, their genomic structural similarities as well as phylogenetic divergence suggest an independent evolution. Until now elementary evidence was provided for the presence of T6SS in the genomes of Pseudomonas entomophila (Pen), an aggressive insect pathogen as well as the human opportunistic pathogen Pseudomonas mendocina (Pme). In this report we evidenced by in silico genome mining along with bioinformatic analysis the presence of genes encoding for putative T6SS core components and secreted proteins in the sequenced Pen L48 and Pme ymp, strains and designated their putative promoters, sigma factors binding sites and various regulatory proteins. Moreover, we investigated the phylogenetic relatedness of four T6SS core proteins from these strains with their orthologues from various Pseudomonas species. Our analysis revealed two phylogenetically distinguishable T6SS loci in the genome of Pme that appeared to be highly homologous to Pseudomonas aeruginosa Hcp-Secretion Island-I (HSI-I) and -II. Our findings suggest that Pme could be excellent additional to P. aeruginosa model, for the elucidation of HSI-I and -II biological role(s), avoiding the overlapping activity HSI-III (Lesic et al., 2009), which is missing from Pme's genome. Likewise, our analysis revealed the presence of a unique entire T6SS in Pen genome, which appears to be phylogenetically close to Pme T6SS-II and P. aeruginosa HSI-II. Since Pen lacks the common secretion systems T3SS and T4SS, the single T6SS locus could have an enforced role in the insect-bacterial interactions, providing thus a promising model for studying its biological function.
在宿主-细菌相互作用中，已经阐述了多种分子转运机制，包括各种分泌系统。新描述的类型 VI 分泌系统（T6SS）似乎通过充当纳米注射器参与细菌发病机制，将几种效应蛋白转运到真核宿主细胞质中。最近的证据表明 T6SS 机制参与了细菌间的相互作用。几种假单胞菌被发现具有多个组织良好的 T6SS 基因座，但它们的基因组结构相似性以及系统发育分歧表明它们是独立进化的。到目前为止，已经提供了假单胞菌昆虫病原（Pen）和人类机会性病原体假单胞菌门多明哥（Pme）基因组中存在 T6SS 的基本证据。在本报告中，我们通过对测序的 Pen L48 和 Pme ymp 菌株的基因组进行计算机挖掘以及生物信息学分析，证明了存在编码 T6SS 核心成分和分泌蛋白的基因，并对其推定启动子、sigma 因子结合位点和各种调节蛋白进行了鉴定。此外，我们还研究了这两个菌株的四个 T6SS 核心蛋白与来自不同假单胞菌物种的同源蛋白的系统发育关系。我们的分析表明，Pme 基因组中有两个在系统发育上可区分的 T6SS 基因座，它们与铜绿假单胞菌 Hcp-Secretion Island-I（HSI-I）和 -II 高度同源。我们的研究结果表明，Pme 可以成为铜绿假单胞菌模型的极好补充，用于阐明 HSI-I 和 -II 的生物学作用，避免了重叠的 HSI-III（Lesic 等人，2009 年）活性，而 Pme 的基因组中缺少 HSI-III。同样，我们的分析表明，Pen 基因组中存在一个独特的完整 T6SS，它在系统发育上与 Pme T6SS-II 和铜绿假单胞菌 HSI-II 接近。由于 Pen 缺乏常见的分泌系统 T3SS 和 T4SS，单个 T6SS 基因座可能在昆虫-细菌相互作用中具有强制作用，因此为研究其生物学功能提供了一个有前途的模型。
