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Legionella encodes multiple classes of Type IV Secretion Systems (T4SSs), including the Dot/Icm protein secretion system that is essential for intracellular multiplication in amoebal and human hosts. Other T4SSs not essential for virulence are thought to facilitate the acquisition of niche-specific adaptation genes including the numerous effector genes that are a hallmark of this genus. Previously, we identified two novel gene clusters in the draft genome of Legionella pneumophila strain 130b that encode homologues of a subtype of T4SS, the genomic island-associated T4SS (GI-T4SS), usually associated with integrative and conjugative elements (ICE). In this study, we performed genomic analyses of 14 homologous GI-T4SS clusters found in eight publicly available Legionella genomes and show that this cluster is unusually well conserved in a region of high plasticity. Phylogenetic analyses show that Legionella GI-T4SSs are substantially divergent from other members of this subtype of T4SS and represent a novel clade of GI-T4SSs only found in this genus. The GI-T4SS was found to be under purifying selection, suggesting it is functional and may play an important role in the evolution and adaptation of Legionella. Like other GI-T4SSs, the Legionella clusters are also associated with ICEs, but lack the typical integration and replication modules of related ICEs. The absence of complete replication and DNA pre-processing modules, together with the presence of Legionella-specific regulatory elements, suggest the Legionella GI-T4SS-associated ICE is unique and may employ novel mechanisms of regulation, maintenance and excision. The Legionella GI-T4SS cluster was found to be associated with several cargo genes, including numerous antibiotic resistance and virulence factors, which may confer a fitness benefit to the organism. The in-silico characterisation of this new T4SS furthers our understanding of the diversity of secretion systems involved in the frequent horizontal gene transfers that allow Legionella to adapt to and exploit diverse environmental niches.
Pubmed ID: 24358157 RIS Download
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Software package for DNA and protein sequence alignment to find regions of local or global similarity between Protein or DNA sequences, either by searching Protein or DNA databases, or by identifying local duplications within a sequence.
View all literature mentionsWeb phylogeny server based on the maximum-likelihood principle.
View all literature mentionsApplication that uses molecular sequence data to compute unrooted phylogenetic networks. Given an alignment of sequences, a distance matrix, or a set of trees, the program will compute a phylogenetic tree or network using methods such as split decomposition, neighbor-net, consensus network, super networks methods or methods for computing hybridization or simple recombination networks.
View all literature mentionsSource code that infers approximately-maximum-likelihood phylogenetic trees from alignments of nucleotide or protein sequences. It uses the Jukes-Cantor or generalized time-reversible (GTR) models of nucleotide evolution and the JTT, WAG, or LG models of amino acid evolution.
View all literature mentionsWeb application for prediction of the presence and location of signal peptide cleavage sites in amino acid sequences from different organisms. The method incorporates a prediction of cleavage sites and a signal peptide/non-signal peptide prediction based on a combination of several artificial neural networks.
View all literature mentionsThe SciCrunch Infrastructure was developed as a cooperative data platform to be used by diverse communities in making data more FAIR.
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