Whole genome sequence analysis reveals the broad distribution of the RtxA type 1 secretion system and four novel putative type 1 secretion systems throughout the Legionella genus

Autoři: Connor L. Brown aff001;  Emily Garner aff001;  Guillaume Jospin aff004;  David A. Coil aff004;  David O. Schwake aff005;  Jonathan A. Eisen aff004;  Biswarup Mukhopadhyay aff002;  Amy J. Pruden aff001
Působiště autorů: Via Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA, United States of America aff001;  Department of Biochemistry, Virginia Tech, Blacksburg, VA, United States of America aff002;  Department of Civil and Environmental Engineering, West Virginia University, Morgantown, WV, United States of America aff003;  Genome Center, University of California, Davis, CA, United States of America aff004;  Department of Natural Sciences, Middle Georgia State University, Macon, GA, United States of America aff005;  Evolution and Ecology, Medical Microbiology and Immunology, University of California, Davis, CA, United States of America aff006
Vyšlo v časopise: PLoS ONE 15(1)
Kategorie: Research Article
doi: https://doi.org/10.1371/journal.pone.0223033


Type 1 secretion systems (T1SSs) are broadly distributed among bacteria and translocate effectors with diverse function across the bacterial cell membrane. Legionella pneumophila, the species most commonly associated with Legionellosis, encodes a T1SS at the lssXYZABD locus which is responsible for the secretion of the virulence factor RtxA. Many investigations have failed to detect lssD, the gene encoding the membrane fusion protein of the RtxA T1SS, in non-pneumophila Legionella, which has led to the assumption that this system is a virulence factor exclusively possessed by L. pneumophila. Here we discovered RtxA and its associated T1SS in a novel Legionella taurinensis strain, leading us to question whether this system may be more widespread than previously thought. Through a bioinformatic analysis of publicly available data, we classified and determined the distribution of four T1SSs including the RtxA T1SS and four novel T1SSs among diverse Legionella spp. The ABC transporter of the novel Legionella T1SS Legionella repeat protein secretion system shares structural similarity to those of diverse T1SS families, including the alkaline protease T1SS in Pseudomonas aeruginosa. The Legionella bacteriocin (1–3) secretion systems T1SSs are novel putative bacteriocin transporting T1SSs as their ABC transporters include C-39 peptidase domains in their N-terminal regions, with LB2SS and LB3SS likely constituting a nitrile hydratase leader peptide transport T1SSs. The LB1SS is more closely related to the colicin V T1SS in Escherichia coli. Of 45 Legionella spp. whole genomes examined, 19 (42%) were determined to possess lssB and lssD homologs. Of these 19, only 7 (37%) are known pathogens. There was no difference in the proportions of disease associated and non-disease associated species that possessed the RtxA T1SS (p = 0.4), contrary to the current consensus regarding the RtxA T1SS. These results draw into question the nature of RtxA and its T1SS as a singular virulence factor. Future studies should investigate mechanistic explanations for the association of RtxA with virulence.

Klíčová slova:

Genetic loci – Legionella – Outer membrane proteins – Phylogenetic analysis – Proteases – Secretion systems – Sequence alignment – Legionella pneumophila


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