Assessing the impact, genomics and evolution of type II secretion across a large, medically important genus: the
Richard C White1, Nicholas P Cianciotto1
11 Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, IL 60611, USA.
Abstract:
The type II secretion system (T2SS) plays a major role in promoting bacterial survival in the environment and in human hosts. One of the best characterized T2SS is that of Legionella pneumophila, the agent of Legionnaires' disease. Secreting at least 25 proteins, including degradative enzymes, eukaryotic-like proteins and novel effectors, this T2SS contributes to the ability of L. pneumophila to grow at low temperatures, infect amoebal and macrophage hosts, damage lung tissue, evade the immune system, and undergo sliding motility. The genes encoding the T2SS are conserved across the genus Legionella, which includes 62 species and >30 pathogens in addition to L. pneumophila. The vast majority of effectors associated with L. pneumophila are shared by a large number of Legionella species, hinting at a critical role for them in the ecology of Legionella as a whole. However, no other species has the same repertoire as L. pneumophila, with, as a general rule, phylogenetically more closely related species sharing similar sets of effectors. T2SS effectors that are involved in infection of a eukaryotic host(s) are more prevalent throughout Legionella, indicating that they are under stronger selective pressure. The Legionella T2SS apparatus is closest to that of Aquicella (another parasite of amoebae), and a significant number of L. pneumophila effectors have their closest homologues in Aquicella. Thus, the T2SS of L. pneumophila probably originated within the order Legionellales, with some of its effectors having arisen within that Aquicella-like progenitor, while other effectors derived from the amoebal host, mimiviruses, fungi and less closely related bacteria.
Insights
The type II secretion system (T2SS) in Legionella pneumophila is crucial for bacterial survival and virulence. Its diverse effectors, shared across Legionella species, highlight their ecological importance and evolutionary origins.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- The type II secretion system (T2SS) is essential for bacterial survival and virulence, particularly in pathogens like Legionella pneumophila.
- Legionella pneumophila causes Legionnaires' disease, utilizing its T2SS to secrete numerous proteins that facilitate host infection and environmental adaptation.
Purpose of the Study:
- To investigate the role and evolutionary origins of the T2SS and its effectors in Legionella species.
- To understand the contribution of T2SS to the pathogenesis and ecological adaptability of Legionella.
Main Methods:
- Comparative genomics analysis of T2SS genes and effectors across Legionella species.
- Phylogenetic analysis to determine the evolutionary relationships of T2SS components.
- Bioinformatic analysis to identify effector origins from various sources like hosts and other microbes.
Main Results:
- The T2SS is conserved across the genus Legionella, with a large proportion of effectors shared among species.
- Legionella pneumophila possesses a unique repertoire of T2SS effectors, with variations correlating with phylogenetic relatedness.
- Effectors involved in eukaryotic host infection are more widespread, suggesting strong selective pressure.
Conclusions:
- The Legionella T2SS apparatus likely originated within the Legionellales order, with contributions from an Aquicella-like progenitor.
- Effectors have diverse origins, including horizontal gene transfer from amoebae, viruses, fungi, and bacteria.
- T2SS plays a critical role in Legionella's ecological success and pathogenic potential.
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