Experimental Investigation Of Interactions Between Dissimilatory Iron Reducing Bacteria And Organic Clay Mineral

Iron is the fourth most abundant element in the Earth’s crust and is ubiquitous in clay minerals. Clay minerals are ubiquitous in soils, sediments, and sedimentary rocks. Organic matters in sediments are usually associated with clay minerals due to their large specific area, surface activity and cation exchange capacity. Clay minerals have contributed significantly to the rise of atmospheric oxygen through the adsorption, concentration, and subsequent burial of significant amounts of organic matter from the terrestrial environment. Microorganism is the core participant of iron cycle in the earth surface. The dissimilatory iron redox is the key driver of natural iron cycle. The study of interactions between microbes and organic clay minerals plays an important role in the cycle of chemical elements, such as Si、Al、Fe and C,contaminant migration, organic matter maturation, and petroleum production.In this study, the preservation of organic matter in clay minerals under microbial activities and the utilization of organic matters in clay minerals by microorganisms were both investigated, making a primary exploration of interactions between microbes and organic clay minerals.The preservation of organic matter in clay minerals under microbial activities was investigated by using 12-Aminolauric acid(ALA)-iron-rich nontronite(NAu-2) complex( ALA-NAu-2), in which ALA, as a model organic molecule, was intercalated into NAu-2. Thermophilic iron-reducing bacteria Thermus scotoductus SA-01(65oC) and hyperthermophilic archaeon Geoglobus ahangari(85oC) were selected as dissimilatory iron reducing bacterium. Our results indicated that intercalated ALA inhibit the extent of Fe(III) reduction by microbes, and it was partially released from nontronite structure, which was correlated with the extent of Fe3+ reduction due to reductive dissolution. However, microbial reduction ability is limited(<30%), organic matter within the smectite structure should be effectively protected against microbial activities. Otherwise, the intercalated ALA released more in hyperthermal environment than thermal environment, indicating that the higher temperature was an unfavorable factor to the preservation of organic matter.In the study of the utilization of organic matters in clay minerals by microorganisms, thermophilic bacteria Thermus scotoductus SA-01 and mesophilic bacteria Shewanella putrefaciens CN32 were selected to reduce structural Fe(Ⅲ) in the nontronite NAu-2 without other carbon source. Experimental results demonstrated that: compared with Shewanella putrefaciens CN-32, Thermus scotoductus SA-01 can effectively use organic matter in NAu-2 as the carbon source. We concluded that the reductive dissolution happens when structural Fe(Ⅲ) in clay minerals is being reduced by microbes. The organic matter associated with nontronite is released into the aqueous solution due to reductive dissolution of nontronite. The organic compounds released from clay minerals are complicated, the rate and the type of organic compound released into solution differ under different temperatures.