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Title: A pangenomic atlas reveals eco-evolutionary dynamics that shape type VI secretion systems in plant-pathogenic Ralstonia
ABSTRACT SoilborneRalstonia solanacearumspecies complex (RSSC) pathogens disrupt microbial communities as they invade roots and fatally wilt plants. RSSC pathogens secrete antimicrobial toxins using a type VI secretion system (T6SS). To investigate how evolution and ecology have shaped the T6SS of these bacterial pathogens, we analyzed the T6SS gene content and architecture across the RSSC and their evolutionary relatives. Our analysis reveals that two ecologically similar Burkholderiaceae taxa, xylem-pathogenic RSSC andParacidovorax, have convergently evolved to wield large arsenals of T6SS toxins. To understand the mechanisms underlying genomic enrichment of T6SS toxins, we compiled an atlas of 1,066 auxiliary T6SS toxin clusters (“aux” clusters) across 99 high-quality RSSC genomes. We classified 25 types ofauxclusters with toxins that predominantly target lipids, nucleic acids, or unknown cellular substrates. Theauxclusters were located in diverse genetic neighborhoods and had complex phylogenetic distributions, suggesting frequent horizontal gene flow. Phages and other mobile genetic elements account for most of theauxcluster acquisition on the chromosome but very little on the megaplasmid. Nevertheless, RSSC genomes were more enriched inauxclusters on the megaplasmid. Although the single, ancestral T6SS was broadly conserved in the RSSC, the T6SS has been convergently lost in atypical, non-soilborne lineages. Overall, our data suggest dynamic interplay between the lifestyle of RSSC lineages and the evolution of T6SSes with robust arsenals of toxins. This pangenomic atlas poises the RSSC as an emerging, tractable model to understand the role of the T6SS in shaping pathogen populations.IMPORTANCEWe explored the eco-evolutionary dynamics that shape the inter-microbial warfare mechanisms of a globally significant plant pathogen, theRalstonia solanacearumspecies complex. We discovered that mostRalstoniawilt pathogens have evolved extensive and diverse repertoires of type VI secretion system-associated antimicrobial toxins. These expansive toxin arsenals potentially enhance the ability ofRalstoniapathogens to invade plant microbiomes, enabling them to rapidly colonize and kill their host plants. We devised a classification system to categorize theRalstoniatoxins. Interestingly, many of the toxin gene clusters are encoded on mobile genetic elements, including prophages, which may be mutualistic symbionts that enhance the inter-microbial competitiveness ofRalstoniawilt pathogens. Moreover, our findings suggest that the convergent loss of this multi-gene trait contributes to genome reduction in two vector-transmitted lineages ofRalstoniapathogens. Our findings demonstrate that the interplay between microbial ecology and pathogen lifestyle shapes the evolution of a genetically complex antimicrobial weapon.  more » « less
Award ID(s):
2336557
PAR ID:
10587268
Author(s) / Creator(s):
; ; ; ; ; ;
Editor(s):
Ruby, Edward G; Allen, Caitilyn
Publisher / Repository:
American Society for Microbiology
Date Published:
Journal Name:
mBio
Volume:
15
Issue:
10
ISSN:
2150-7511
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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