Characterization of silica-induced protein and mechanism of microbial silica deposition

分子生态技术和地球化学调查的结合表明，生活在地热环境中的嗜热或超嗜热微生物可能与生物成因硅质矿床的形成有关。电镜观察表明，在自然形成的硅质沉积物中，如硅质烧结矿、硅辉石和硅垢中存在许多微生物样织物，这表明微生物对二氧化硅沉淀有贡献。分子系统发育分析表明，热菌属和氢杆菌属的极端嗜热细菌是日本地热发电厂管道和设备硅质沉积物中原生微生物群落的主要组成部分。这些细菌似乎积极地促成了巨大硅质沉积物的快速形成。此外，体外实验表明，Thermus细胞在指数生长阶段诱导过饱和无定形二氧化硅的沉淀，同时产生一种特定的细胞包膜蛋白（silica -induced protein, Sip）。Sip似乎是ABC转运体的一种铁结合质周蛋白。Al离子抑制了Sip的产生。地热热水中溶解的二氧化硅可能是维持微生物在有限生态位中的位置和生存的重要组成部分。

A combined use of molecular ecological techniques and geochemical surveys revealed that thermophilic or hyperthermophilic microorganisms living in the geothermal environments are likely to be implicated in the formation of biogenic siliceous deposits. Electron microscopic observations indicated that numerous microorganism-like fabrics were presented in naturally occurring siliceous deposits such as siliceous sinter, geyserite, and silica scale, which suggests microbial contribution to silica precipitation. Molecular phylogenetic analysis suggested that extreme thermophilic bacteria within the genera Thermus and Hydrogenobacter are predominant components among the indigenous microbial community in siliceous deposits formed in pipes and equipment of Japanese geothermal power plants. These bacteria seem to actively contribute to the rapid formation of huge siliceous deposits. Additionally, in vitro examination suggested that Thermus cells induced the precipitation of supersaturated amorphous silica during the exponential growth phase, concomitant with the production of a specific cell envelope protein (Silica-induced protein, Sip). Sip seems to be a ferric iron-binding periplasmic protein of ABC transporter). The production of Sip was inhibited by Al ion. Dissolved silica in geothermal hot water may be a significant component in the maintenance of position and survival of microorganisms in limited niches.