Bachelor Thesis

Arsenite transformation in the presence of sulfide by Alkalilimnicola ehrlichii (MLHE-1)

Carolin Kerl (08/2012-08/2013)

Support: Britta Planer-Friedrich, Frank Thomas

The formation of thioarsenates plays an important role in anoxic water layers with naturally high arsenite and sulfide concentrations, like for example Mono Lake in California, USA. By conducting growth experiments in arsenic-rich anaerobic water the influence of sulfide on the growth of Alkalilimnicola ehrlichii (MLHE-1), a bacterium originally isolated from Mono Lake (pH 9.8), was tested. A. ehrlichii can convert equimolar concentrations of arsenite and nitrate completely to arsenate and nitrite. It was shown that A. ehrlichii is capable of oxidizing sulfide to polysulfides and elemental sulfur as well as arsenite to arsenate. The percentage of formed thioarsenates was higher in medium than in deionized water. Trithioarsenate was the dominant species in medium and dithioarsenate in deionized water. The formed thioarsenates were not transformed by A. ehrlichii. Due to the fact that a chemical equilibrium is formed between thioarsenates and sulfide in the medium, thioarsenates transform to arsenate and sulfide as soon as the sulfide concentration in the medium decreases. Furthermore, the growth of A. ehrlichii directly with monothioarsenate and different nitrate concentrations was investigated. No microbial growth was found in any of the experiments as monothioarsenate stayed stable during the experiments. Arsenite or monothioarsenate were not decomposed in any of the abiotic control experiments. Overall the experiments showed that thioarsenates play an important role in the As-S-cycle and transform abiotically due to microbial sulfide oxidation, but it seems that they could not be transformed directly by A. ehrlichii.