An Aggregation-defective Mutant of <i>Methanothermobacter</i> sp. CaT2 Reveals Unique Protein-dependent Aggregation

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  • Sumikawa Kana
    Applied Molecular Bioscience, Graduates School of Medicine, Yamaguchi University
  • Kosaka Tomoyuki
    Department of Biological Chemistry, College of Agriculture, Graduates School of Science and Technology for Innovation, Yamaguchi University Research Center for Thermotolerant Microbial Resources, Yamaguchi University
  • Mayahara Noriaki
    Applied Molecular Bioscience, Graduates School of Medicine, Yamaguchi University
  • Matsutani Minenosuke
    Department of Biological Chemistry, College of Agriculture, Graduates School of Science and Technology for Innovation, Yamaguchi University
  • Udo Koichi
    Science Research Center, Yamaguchi University
  • Yamada Mamoru
    Applied Molecular Bioscience, Graduates School of Medicine, Yamaguchi University Department of Biological Chemistry, College of Agriculture, Graduates School of Science and Technology for Innovation, Yamaguchi University Research Center for Thermotolerant Microbial Resources, Yamaguchi University

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  • An Aggregation-defective Mutant of Methanothermobacter sp. CaT2 Reveals Unique Protein-dependent Aggregation

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<p>The thermophilic hydrogenotrophic methanogen, Methanothermobacter sp. CaT2, which possesses an extracellular sugar layer, commonly aggregates by itself or with other microorganisms. To elucidate the molecular mechanisms responsible for this aggregation, the aggregation-defective mutant, CLA160, was isolated. Optical and electron microscopy observations revealed that the mutant exhibited a significant reduction in aggregation. Genomic sequencing showed that CLA160 has a single point mutation, causing a nonsense mutation in MTCT_1020, which encodes a hypothetical protein. Motif and domain analyses indicated that the hypothetical protein bears two membrane-spanning segments at the N- and C-terminal regions and a large middle repeat-containing region. The results of a bioinformatic analysis suggested that the first middle region (RII) of the protein or the whole structure is responsible for the function of the product of MTCT_1020 in the aggregation of CaT2. A treatment with proteinase K suppressed sedimentation in CaT2, indicating a reduction in aggregation, with almost no effect on sedimentation in CLA160. The addition of Ca2+ or Mg2+ ions enhanced sedimentation in CaT2, whereas a DNase treatment had no effect on sedimentation in either strain. These results suggest that the hypothetical protein encoded by MTCT_1020 plays a key role as a membrane-bound adhesion protein in the aggregation of CaT2, which is enhanced by the addition of Ca2+ or Mg2+ ions.</p>

Journal

  • Microbes and Environments

    Microbes and Environments 34 (3), 244-251, 2019

    Japanese Society of Microbial Ecology / Japanese Society of Soil Microbiology / Taiwan Society of Microbial Ecology / Japanese Society of Plant Microbe Interactions / Japanese Society for Extremophiles

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