Maiko Harada

Publications (2)12.59 Total impact

• Article: Expression of genes for sulfur oxidation in the intracellular chemoautotrophic symbiont of the deep-sea bivalve Calyptogena okutanii.

  Maiko Harada, Takao Yoshida, Hirokazu Kuwahara, Shigeru Shimamura, Yoshihiro Takaki, Chiaki Kato, Tetsuya Miwa, Hiroshi Miyake, Tadashi Maruyama
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  ABSTRACT: To understand sulfur oxidation in thioauto-trophic deep-sea clam symbionts, we analyzed the recently reported genomes of two chemoautotrophic symbionts of Calyptogena okutanii (Candidatus Vesicomyosocius okutanii strain HA: Vok) and C. magnifica (Candidatus Ruthia magnifica strain Cm: Rma), and examined the sulfur oxidation gene expressions in the Vok by RT-PCR. Both symbionts have genes for sulfide-quinone oxidoreductase (sqr), dissimilatory sulfite reductase (dsr), reversible dissimilatory sulfite reductase (rdsr), sulfur-oxidizing multienzyme system (sox)(soxXYZA and soxB but lacking soxCD), adenosine phosphosulfate reductase (apr), and ATP sulfurylase (sat). While these genomes share 29 orthologous genes for sulfur oxidation implying that both symbionts possess the same sulfur oxidation pathway, Rma has a rhodanese-related sulfurtransferase putative gene (Rmag0316) that has no corresponding ortholog in Vok, and Vok has one unique dsrR (COSY0782). We propose that Calyptogena symbionts oxidize sulfide and thiosulfate, and that sulfur oxidation proceeds as follows. Sulfide is oxidized to sulfite by rdsr. Sulfite is oxidized to sulfate by apr and sat. Thiosulfate is oxidized to zero-valence sulfur by sox, which is then reduced to sulfide by dsr. In addition, thiosulfate may also be oxidized into sulfate by another component of sox. The result of the RT-PCR showed that genes (dsrA, dsrB, dsrC, aprA, aprB, sat, soxB, and sqr) encoding key enzymes catalyzing sulfur oxidation were all equally expressed in the Vok under three different environmental conditions (aerobic, semioxic, and aerobic under high pressure at 9 MPa), indicating that all sulfur oxidation pathways function simultaneously to support intracellular symbiotic life.
  Extremophiles 10/2009; 13(6):895-903. · 2.94 Impact Factor
• Article: Reduced genome of the thioautotrophic intracellular symbiont in a deep-sea clam, Calyptogena okutanii.

  Hirokazu Kuwahara, Takao Yoshida, Yoshihiro Takaki, Shigeru Shimamura, Shinro Nishi, Maiko Harada, Kazuyo Matsuyama, Kiyotaka Takishita, Masaru Kawato, Katsuyuki Uematsu, Yoshihiro Fujiwara, Takako Sato, Chiaki Kato, Masanari Kitagawa, Ikunoshin Kato, Tadashi Maruyama
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  ABSTRACT: Although dense animal communities at hydrothermal vents and cold seeps rely on symbioses with chemoautotrophic bacteria [1, 2], knowledge of the mechanisms underlying these chemosynthetic symbioses is still fragmentary because of the difficulty in culturing the symbionts and the hosts in the laboratory. Deep-sea Calyptogena clams harbor thioautotrophic bacterial symbionts in their gill epithelial cells [1, 2]. They have vestigial digestive tracts and nutritionally depend on their symbionts [3], which are vertically transmitted via eggs [4]. To clarify the symbionts' metabolic roles in the symbiosis and adaptations to intracellular conditions, we present the complete genome sequence of the symbiont of Calyptogena okutanii. The genome is a circular chromosome of 1,022,154 bp with 31.6% guanine + cytosine (G + C) content, and is the smallest reported genome in autotrophic bacteria. It encodes 939 protein-coding genes, including those for thioautotrophy and for the syntheses of almost all amino acids and various cofactors. However, transporters for these substances to the host cell are apparently absent. Genes that are unnecessary for an intracellular lifestyle, as well as some essential genes (e.g., ftsZ for cytokinesis), appear to have been lost from the symbiont genome. Reductive evolution of the genome might be ongoing in the vertically transmitted Calyptogena symbionts.
  Current Biology 06/2007; 17(10):881-6. · 9.65 Impact Factor