Bachelor Thesis

The influence of arsenic on iron mobilisation via sulfur-electron shuttling by S.deleyianum

Anja Schnell (11/2012-09/2013)

Support: Britta Planer-Friedrich, Regina Lohmayer

Sulfurospirillum deleyianum as a sulfur reducing bacteria is able to reduce Fe(III) indirectly by means of sulfur-electron-shuttling and is maybe able to even use arsenate as an electron acceptor. Therefore, it can promote the release of arsenic, which is bound to the surface of iron oxides. Microcosm experiments were conducted with S. deleyianum in absence and presence of thiosulfate and ferrihydrite. Bacteria were provided with formate as electron donor, acetate as carbon source, cysteine as sulfur source and either arsenite, arsenate or monothioarsenate as electron acceptor. The samples were analyzed for cysteine via HPLC, for iron and sulfide via photometry, as well as for changes in arsenic and sulfur species by IC-ICP-MS. The results indicated that Fe(III) was reduced completely in presence of arsenic, though supply of arsenate as sole electron acceptor did not cause significant growth of S. deleyianum. Furthermore, despite the presence of arsenic and sulfide, no significant formation of thioarsenates occurred. Hence, their role as potential sulfide reservoir alternative to FeS precipitation could not be proved. Based on total arsenic analysis, marked differences between different solutions were detected, with mobilization of arsenic occurring in the arsenite solution and fixation of arsenic in the arsenate solution. However, speciation data did not allow transfer of known mobilization and sorption theories for arsenite and arsenate, because of similarities in arsenic speciation. Hence, further experiments are required in order to improve experimental conditions and gain a better understanding of the occurring processes.