Non-destructive speciation of iron sulfides formed by sulfate-reducing bacteria in river sediments and estimation of the formation process.

为了阐明硫酸盐还原菌在河口沉积物铁硫体系反应机理中的作用，进行了多方面的研究。首先研究了几个河口地区沉积物中硫酸盐还原细菌和黄铁矿(FeS_2)的垂直分布，其中包括塔玛河，这是一条主要的城市河流。对于黄铁矿的检测，应用了穆斯堡尔光谱，这是表征铁的化学状态的最有用的非破坏性手段之一。在琼脂平板上用菌落计数法计算硫酸盐还原菌活菌数。对人类影响较大的北九肯河和人类影响较小的滨海滩涂的沉积物也进行了调查。结果表明，硫酸盐还原菌的垂直分布与黄铁矿的垂直分布基本一致。其次，利用硫酸盐…进行了培养实验多还原细菌(Desulfovibrio sp.)从塔玛河河口沉积物中分离出来。在厌氧条件下，将细菌培养在含有硫酸盐离子和三种浓度的亚铁离子(40ppm，80ppm和200ppm)的30℃的培养基中。在适当的孵育时间后，用离心法分离培养液中产生的沉淀物，冷冻停止生物活性，然后测量Moessbauer谱。铁浓度影响产物的化学变化，表明硫酸盐还原菌辅助的培养产物不能用硫化物离子与亚铁离子的简单无机反应来解释。X-射线吸收精细结构测量结果表明，几天后孵化产物中的铁原子与硫配位，而初始沉淀中的铁原子与氧配位。这些事实有力地表明，硫酸盐还原细菌是河口沉积物中黄铁矿形成的原因。较少

In this study, various investigations were performed in order to clarify the contribution of sulfate-reducing bacteria to the reaction mechanism of iron-sulfur system in estuarine sediments. At first, vertical distributions of sulfate-reducing bacteria and pyrite (FeS_2) in the sediments were examined in several estuarine areas including Tama-river, which is a major and typical urban river. For the detection of pyrite, ^<57>Fe Moessbauer spectroscopy was applied, which is one of the most useful non-destructive means for characterizing the chemical states of iron. The number of living sulfate-reducing bacteria was calculated by a colony counting method on an agar plate. Sediments of Kitajukken-river with large human impact and those of Yatsu-tideland with little human impact were also investigated. The results showed that the vertical distribution of living sulfate-reducing bacteria and that of pyrite agreed well in all areas.Next, the incubation experiment was carried out using sulfate … More -reducing bacteria (Desulfovibrio sp.) isolated from estuarine sediments of Tama-river. The bacteria were incubated in the medium containing sulfate ion and three levels of concentration of ferrous ion (40 ppm,80 ppm and 200 ppm) at 30 degrees under an anaerobic condition. After an appropriate incubation time, the precipitate produced in the medium was separated by centrifugation and bioactivity was stopped by freezing, and then the Moessbauer spectrum was measured. The level of iron concentration affected the chemical change of the products, suggesting that the incubation products with the aid of sulfate-reducing bacteria could not be explained in terms of the simple inorganic reaction of a sulfide ion with a ferrous ion. The result of X-ray absorption fine structure measurements showed that iron atoms were coordinated by sulfur in the incubation products after several days, whereas they were coordinated by oxygen in the initial precipitate. These facts strongly suggest that the sulfate-reducing bacteria are responsible for the pyrite formation in estuarine sediments. Less