Jon R. Lloyd

Potential role of the Fe(III)-reducing bacteria Geobacter and Geothrix in controlling arsenic solubility in Bengal delta sediments

Abstract Previous studies from our laboratory have suggested a role for indigenous metal-reducing bacteria in the reduction of sediment-bound As(V), and have also shown that a stable enrichment culture of Fe(III)-reducing bacteria was able to mobilize arsenic (as As(III)) from sediments collected from West Bengal (Islam et al, 2004). To identify the Fe(III)-reducing bacteria that may play a role in the reduction of As(V) and mobilization of As(III), we made a detailed molecular analysis of this enrichment culture. It was dominated by a close relative of Geothrix fermentans, but the type strain of this organism was unable to conserve energy for growth via the dissimilatory reduction of As(V), or reduce As(V) present in a defined medium containing fumarate as the electron acceptor. Furthermore, when the cells were grown using soluble Fe(III)-Citrate as an electron acceptor in the presence of As(V), bacterial Fe(III) reduction resulted in the precipitation of the Fe(II)-bearing mineral vivianite in 2 weeks. This was accompanied by the efficient removal of As from solution. These results demonstrate that Geothrix fermentans, in common with other key Fe(III)-reducing bacteria such as Geobacter sulfurreducens, does not reduce As(V) enzymatically, but can capture arsenic in Fe(II) minerals formed during respiration using Fe(III) as an electron acceptor. Thus, the reduction of arsenicbearing Fe(III) oxide minerals is not sufficient to mobilize arsenic, but may result in the formation of Fe(II) biominerals that could potentially act as sinks for arsenic in sediments. Additional mechanisms, including dissimilatory As(V) reduction by other specialist anaerobic bacteria, are implicated in the mobilization of arsenic from sediments.

Chapter 11 Biochemical basis of microbe-radionuclide interactions

Publisher Summary This chapter discusses biochemical basis of microbe–radionuclide interactions. Microbial metabolism can significantly alter the mobility of radionuclides in the environment and is increasingly being proposed as the basis of novel remediation programmes. Enzymatically catalyzed redox transformations are discussed with respect to radionuclides, including U, Np, Pt, and Tc. Metabolism dependent uptake of radionuclides—such as Cs—are discussed in the chapter. The biochemical basis of indirect biomineralization processes driven by microbial products—including sulfide, phosphate and iron minerals—is reviewed. The broad range of techniques available to help characterize such transformations is also explained. The microbial reduction of technetium is used as a case study to illustrate the integrated use of (1) advanced spectroscopic techniques to characterize end products of radionuclide transformations, (2) physiological studies to characterize biochemical pathways of importance, and (3) the construction of defined mutants by using molecular biology to confirm the involvement of key enzymes in radionuclide transformations.

Geological repositories: scientific priorities and potential high-technology transfer from the space and physics sectors

Abstract The use of underground geological repositories, such as in radioactive waste disposal (RWD) and in carbon capture (widely known as Carbon Capture and Storage; CCS), constitutes a key environmental priority for the 21st century. Based on the identification of key scientific questions relating to the geophysics, geochemistry and geobiology of geodisposal of wastes, this paper describes the possibility of technology transfer from high-technology areas of the space exploration sector, including astrobiology, planetary sciences, astronomy, and also particle and nuclear physics, into geodisposal. Synergies exist between high technology used in the space sector and in the characterization of underground environments such as repositories, because of common objectives with respect to instrument miniaturization, low power requirements, durability under extreme conditions (in temperature and mechanical loads) and operation in remote or otherwise difficult to access environments.