Expression-based identification of genetic determinants of the bacterial symbiosis ‘Chlorochromatium aggregatum

Authors

  • Roland Wenter,

    1. Bereich Mikrobiologie, Department Biologie I, Ludwig-Maximilians-Universität München, Großhadernerstrasse 2-4, D-82152 Planegg-Martinsried, Germany.
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  • Katharina Hütz,

    1. Bereich Mikrobiologie, Department Biologie I, Ludwig-Maximilians-Universität München, Großhadernerstrasse 2-4, D-82152 Planegg-Martinsried, Germany.
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  • Dörte Dibbern,

    1. Bereich Mikrobiologie, Department Biologie I, Ludwig-Maximilians-Universität München, Großhadernerstrasse 2-4, D-82152 Planegg-Martinsried, Germany.
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  • Tao Li,

    1. Department of Biochemistry and Molecular Biology, The Pennsylvania State University, S-234 Frear Building, University Park, PA 16802, USA.
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    • Present addresses: Algal Genomics Research Group, Institute of Hydrobiology, Chinese Academy of Sciences, No. 7 Donghu South Road, Wuhan 430072, China;

  • Veronika Reisinger,

    1. Bereich Botanik, Department Biologie I, Ludwig-Maximilians-Universität München, Großhadernerstrasse 2-4, D-82152 Planegg-Martinsried, Germany.
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    • Center for Organelle Research (CORE), University of Stavanger, Kristine Bonnevis vei 22, N-4036 Stavanger, Norway;

  • Matthias Plöscher,

    1. Bereich Botanik, Department Biologie I, Ludwig-Maximilians-Universität München, Großhadernerstrasse 2-4, D-82152 Planegg-Martinsried, Germany.
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    • TRION Pharma GmbH, Frankfurter Ring 193a, 80807 München, Germany;

  • Lutz Eichacker,

    1. Bereich Botanik, Department Biologie I, Ludwig-Maximilians-Universität München, Großhadernerstrasse 2-4, D-82152 Planegg-Martinsried, Germany.
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    • Center for Organelle Research (CORE), University of Stavanger, Kristine Bonnevis vei 22, N-4036 Stavanger, Norway;

  • Brian Eddie,

    1. College of Earth, Ocean, and Environment, University of Delaware, 15 Innovation Way, Newark, DE 19711, USA.
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  • Thomas Hanson,

    1. College of Earth, Ocean, and Environment, University of Delaware, 15 Innovation Way, Newark, DE 19711, USA.
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  • Donald A. Bryant,

    1. Department of Biochemistry and Molecular Biology, The Pennsylvania State University, S-234 Frear Building, University Park, PA 16802, USA.
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  • Jörg Overmann

    Corresponding author
    1. Bereich Mikrobiologie, Department Biologie I, Ludwig-Maximilians-Universität München, Großhadernerstrasse 2-4, D-82152 Planegg-Martinsried, Germany.
      E-mail joerg.overmann@dsmz.de; Tel. (+49) 531 2616 352; Fax (+49) 531 2616 418.
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    • Deutsche Sammlung von Mikroorganismen und Zellkulturen (DSMZ), Inhoffenstraße 7B, 38124 Braunschweig


E-mail joerg.overmann@dsmz.de; Tel. (+49) 531 2616 352; Fax (+49) 531 2616 418.

Summary

The phototrophic consortium ‘Chlorochromatium aggregatum’ is a highly structured association of green sulfur bacterial epibionts surrounding a central, motile bacterium and is the most specific symbiosis currently known between two phylogenetically distinct bacterial species. Genes and gene products potentially involved in the symbiotic interaction were identified on the genomic, transcriptomic and proteomic level. As compared with the 11 available genomes of free-living relatives, only 186 open reading frames were found to be unique to the epibiont genome. 2-D differential gel electrophoresis (2-D DIGE) of the soluble proteomes recovered 1612 protein spots of which 54 were detected exclusively in consortia but not in pure epibiont cultures. Using mass spectrometry analyses, the 13 most intense of the 54 spots could be attributed to the epibiont. Analyses of the membrane proteins of consortia, of consortia treated with cross-linkers and of pure cultures indicated that a branched chain amino acid ABC-transporter binding protein is only expressed in the symbiotic state of the epibiont. Furthermore, analyses of chlorosomes revealed that an uncharacterized 11 kDa epibiont protein is only expressed during symbiosis. This protein may be involved in the intracellular sorting of chlorosomes. Application of a novel prokaryotic cDNA suppression subtractive hybridization technique led to identification of 14 differentially regulated genes, and comparison of the transcriptomes of symbiotic and free-living epibionts indicated that 328 genes were differentially transcribed. The three approaches were mostly complementary and thereby yielded a first inventory of 352 genes that are likely to be involved in the bacterial interaction in ‘C. aggregatum’. Notably, most of the regulated genes encoded components of central metabolic pathways whereas only very few (7.5%) of the unique ‘symbiosis genes’ turned out to be regulated under the experimental conditions tested. This pronounced regulation of central metabolic pathways may serve to fine-tune the symbiotic interaction in ‘C. aggregatum’ in response to environmental conditions.

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