報告書番号

U99056

タイトル（和文）

石炭の生物加工-15- --黄鉄鉱吸着因子、ラスチシアニン遺伝子の多様性--

タイトル（英文）

Bio-processing if coal -15-Diversity of pyrite-binding protein, rusticyanin from iron-oxidizing bacterium

概要 （図表や脚注は「報告書全文」に掲載しております）

微生物による固体の特異的吸着は，広範に見られる現象であるが，その機構は詳細には理解されていない。当所の微生物石炭脱硫システムでも，鉄酸化細菌の黄鉄鉱への特異的吸着が重要な役割を果たしている。近年，コンクリートの腐食作用などに関しても，微生物吸着が重要な要素であることが分かってきた。 本報告では，吸着の本質を理解するため，鉄酸化細菌の黄鉄鉱吸着因子（ラスチシアニン）の遺伝子を単離・分析し，次のような成果を得た。 ６株の鉄酸化細菌からラスチシアニン遺伝子を単離し，配列を比較した結果，既知のものとは系統を異にするラスチシアニンの存在が明らかになった。系統間の３次元構造の比較から，新たに発見されたラスチシアニンも黄鉄鉱結合能を持つ可能性が示された。また，既知の系統の遺伝子は６株すべてに共通に存在していた。このことから，既知の系統の遺伝子が吸着現象に深く関わっていることが推察された。

概要 （英文）

We have been developing the coal desulfurization technique using iron-oxidizing bacterium, Thiobacillus ferrooxidans as a biological surfactant which can selectively adhere to pyrite existing in pulverized coal. In the former report, we isolated a pyrite-binding protein from T. ferrooxidans. The binding protein was identified as rusticyanin. Rusticyanin is a blue copper protein and it plays an important role in the electron transfer system of the iron oxidation. In spite of its significance, the diversities of its gene have not been discussed. In this study, we cloned seven different genes of rusticyanin from six different strains. We found out that some strains had multiple rusticyanin genes, which had deferent amino acids sequence each other. In addition, a new type rusticyanin existed in some strains incidentally although all strains had the known type one commonly. Between common types and incidental types, sequence similarities were 74.1 to 75.9%. In brief, because four copper binding residues were conserved completely, little difference would exist in their functions. But 44% of amino acids were different in the signal peptide known as a “tag” for protein transports in the cell. On the other hand, in mature protein, 12 out of 20 different amino acids located protein surface. It would cause a difference in protein surface acidity. In the previous report, rusticyanin was found at three areas, cell surface, periplasmic space and inside of inner cell membrane. Because of their extremely acidity growth environment, some strain would select the proper rusticyanin depending on the area. It cloud explain why extra signal peptide existed. The pedigree tree from the analysis of common type rusticyanin genes gave us a hypothesis that an uptake of optional gene occurred at recent era. Therefore the evolution of the optional gene would happen in a strain that we have not known. These hypotheses suggested that the diversity of T. ferrooxidans would be larger than our knowledge. In nature, some strains may have more suitable rusticyanin for the coal desulfurization systems than one from now studying.

報告者

キーワード