A comprehensive study on iodine-metabolizing bacteria: Exploring the origin of thyroid hormones

2019 Fiscal Year Final Research Report

• Project/Area Number: 17H03788
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Applied microbiology
• Research Institution: Chiba University
• Principal Investigator: Amachi Seigo 千葉大学, 大学院園芸学研究科, 教授 (80323393)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: ヨウ素 / 蓄積 / 甲状腺 / 呼吸 / 放射性ヨウ素 / バクテリア

Outline of Final Research Achievements

Localization of iodine in Arenibacter sp. SCT was found to be the membrane fraction, in which iodine was bound to a tyrosine residue of a protein annotated as PAP2 family protein. The PAP2 family is known to include histidine phosphatases and vanadium-dependent haloperoxidases (vHPOs), and the iodinated protein of strain C-21 formed a distinct clade within the vHPOs. Further study is needed to fully understand the function of iodine accumulated in strain C-21.
Dissimilatory iodate reductase (Idr) of Pseudomonas sp. SCT was identified by multiple proteomic and transcriptomic analyses as well as by the construction of a deletion mutant. The large subunit of Idr (IdrA) was a novel member of the DMSO reductase family. It was also suggested that both O2 and H2O2 are formed as by-products of iodate respiration. An electron transport chain model of strain SCT, in which iodate, H2O2, and O2 are used as terminal electron acceptors, was proposed.

Free Research Field

応用微生物学

Academic Significance and Societal Importance of the Research Achievements

ヨウ素蓄積細菌C-21株において、ヨードペルオキシダーゼがヨウ素の取り込みのみならず、ヨウ素の蓄積・貯蔵にも寄与することを初めて明らかにした。蓄積ヨウ素の機能は未だ不明であるが、原始的な甲状腺ホルモンが合成されている可能性もあり、ヨウ素と生物の共進化の謎にせまる興味深い結果が得られた。一方、ヨウ素酸呼吸細菌SCT株において、鍵となる酵素と遺伝子を初めて特定した。同様の遺伝子を持つ細菌は海洋・陸圏に広く分布することから、このような微生物が地球規模でのヨウ素の循環に大きく寄与する可能性がある。またこのような細菌は、放射性ヨウ素（I-129）で汚染された地下水環境の浄化に応用できるかもしれない。