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Title: Lifestyle Evolution in Cyanobacterial Symbionts of Sponges

The “Candidatus Synechococcus spongiarum” group includes different clades of cyanobacteria with high 16S rRNA sequence identity (~99%) and is the most abundant and widespread cyanobacterial symbiont of marine sponges. The first draft genome of a “Ca. Synechococcus spongiarum” group member was recently published, providing evidence of genome reduction by loss of genes involved in several nonessential functions. However, “Ca. Synechococcus spongiarum” includes a variety of clades that may differ widely in genomic repertoire and consequently in physiology and symbiotic function. Here, we present three additional draft genomes of “Ca. Synechococcus spongiarum,” each from a different clade. By comparing all four symbiont genomes to those of free-living cyanobacteria, we revealed general adaptations to life inside sponges and specific adaptations of each phylotype. Symbiont genomes shared about half of their total number of coding genes. Common traits of “Ca. Synechococcus spongiarum” members were a high abundance of DNA modification and recombination genes and a reduction in genes involved in inorganic ion transport and metabolism, cell wall biogenesis, and signal transduction mechanisms. Moreover, these symbionts were characterized by a reduced number of antioxidant enzymes and low-weight peptides of photosystem II compared to their free-living relatives. Variability within the “Ca. Synechococcus spongiarum” group wasmore » mostly related to immune system features, potential for siderophore-mediated iron transport, and dependency on methionine from external sources. The common absence of genes involved in synthesis of residues, typical of the O antigen of free-living Synechococcus species, suggests a novel mechanism utilized by these symbionts to avoid sponge predation and phage attack.« less
 [1] ;  [2] ;  [3] ;  [1] ;  [4] ;  [5] ;  [6] ;  [2] ;  [1]
  1. Univ. of Haifa (Israel). Leon H. Charney School of Marine Sciences
  2. Univ. of Würzburg, Würzburg (Germany). Julius-von-Sachs Institute for Biosciences
  3. Univ. of Chicago, IL (United States). Dept. of Ecology and Evolution
  4. Justus-Liebig-Univ. (Germany)
  5. Argonne National Lab. (ANL), Argonne, IL (United States)
  6. Univ. of Chicago, IL (United States). Dept. of Ecology and Evolution; Argonne National Lab. (ANL), Argonne, IL (United States); Marine Biological Lab., Woods Hole, MA (United States of America); Zhejiang Univ. (China). College of Environmental and Resource Sciences
Publication Date:
OSTI Identifier:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
mBio (Online)
Additional Journal Information:
Journal Name: mBio (Online); Journal Volume: 6; Journal Issue: 3; Journal ID: ISSN 2150-7511
American Society for Microbiology
Research Org:
Argonne National Laboratory (ANL), Argonne, IL (United States)
Sponsoring Org:
Country of Publication:
United States