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Understanding Viral Evolution in Endosymbionts and the Role of Mobile DNA

This article explores the intricate relationship between viral evolution and endosymbionts, focusing on how bacterial genomes adapt during symbiosis. It discusses key mechanisms such as DNA insertions, duplications, and mutations, revealing how genome sizes and variations correlate with ecological factors. The roles of mobile DNA agents like plasmids and bacteriophages in open-source evolution are analyzed. Additionally, the impact of ecological constraints and mobile DNA density on bacterial phylogeny and ecology is examined, providing insights into the evolution of complex life forms.

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Understanding Viral Evolution in Endosymbionts and the Role of Mobile DNA

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  1. Viral Evolution in Endosymbionts Seth Bordenstein Departments of Biological Sciences & Pathology, Microbiology, and Immunology s.bordenstein@vanderbilt.edu February 11, 2012

  2. Symbiosis: “The living together of dissimilar organisms” de Bary 1879

  3. How do bacterial genomes change during symbiosis? Insertions of DNA from foreign sources; Duplications Single nt mutations Gene loss / Genome reduction

  4. The Genome Sizes of Life

  5. Rule 1: Genome Size Variation Correlates with Gene Number Variation Protein Coding Genes Genome Size (Mb)

  6. Eukaryotic cell Rule 2: Bacterial Ecology Alters Genome Evolution DNA Inflow DNA Outflow • Mutation bias for DNA deletions • Relaxed selection on redundant genes between bacteria and host • Reduced exposure to novel gene pools Diagram modified from Mira, A., Ochman, H. & Moran, N.A. 2001. Trends Genet 17, 589-96.

  7. Rule 3: Bacterial Mobile DNAs AreThe Agents of Open Source Evolution Plasmid Bacteriophage Transposon

  8. Ecology Affects Mobile DNA Abundance Free-living Bacteria Obligate Intracellular Bacteria • Exposure to other microbes • Horizontal Gene Transfer • Mobile DNA • Reduced exposure to other microbes • Genome Reduction • Genome Stability

  9. Eukaryotic cell DNA Inflow DNA Outflow DNA Inflow? Mobile DNA? Diagram modified from Mira, A., Ochman, H. & Moran, N.A. 2001. Trends Genet 17, 589-96.

  10. Three Questions • How variable are mobile DNA contents in Bacteria? • Does this variation statistically associate with phylogeny, genome size, or ecology? • How do mobile elements survive and flourish in obligate, intracellular bacteria?

  11. The Genomes of Life Bacteria 2622 Genomes Archaea 147 Genomes Eucarya 166 Genomes

  12. How variable are mobile DNA contents in Bacteria? % Prophage % Plasmid % Transposon Newton & Bordenstein 2011

  13. Is Mobile DNA Gene Density Independentof Phylogeny?

  14. 16S rRNA Tree & Mobile DNA % K statistic Full dataset, K = 0.0024 K > 1 is significant association Mobile DNA % is scattered randomly across the tree Newton & Bordenstein 2011

  15. Do Constraints in Ecology Vary with Mobile DNA Gene Density?

  16. Three Bacterial Ecotypes Extracellular Facultative Free-living world Intracellular world Obligate Intracellular Facultative

  17. Newton & Bordenstein 2011 Extracellular Facultative Free-living world Intracellular world Facultative P < 0.005 P < 0.001 Obligate N = 74 N = 270 N = 40 > >

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