Bachelor Thesis

Degradation of arsenic and sulfur compounds by thermophilic microorganisms

Rita Schubert (11/2010-08/2011)

Support: Britta Planer-Friedrich, Cornelia Härtig

Thermophile bacteria are known to inhabit arsenic- and sulfur-rich alkaline thermal springs. Their degradation of thiosulfate, arsenite and thioarsenates was subject of the present thesis. Incubation experiments were conducted with Thermus thermophilus HB27, an enriched cell culture from Yellowstone National Park (YNP), USA, and Thermocrinis ruber OC1/4 in the laboratory and with natural streamer-samples of Thermocrinis at Conch Spring, YNP. Degradation of arsenic- and sulfur species over time was followed by IC-ICP-MS determinations and cell densities were observed in experiments conducted in the laboratory. Cultivation of the enrichment culture was only possible under permanently aerobic conditions. Thermus thermophilus HB27 showed growth on thiosulfate, monothioarsenate and arsenite, however, it did not catabolize any of those compounds. Thermocrinis ruber and the enrichment culture both showed degradation of thiosulfate to sulfate. Monothioarsenate was assimilated by Thermocrinis in the field and the laboratory. During the process mainly arsenate, sulfate and small quantities of arsenite and thiosulfate were produced. Further oxidation of these compounds could not be unequivocally identified as biotic process. Tetrathiosulfate was unstable in all laboratory experiments. No strain showed growth on tetrathioarsenate. In the field, assimilation and biotic transformation of products formed by abiotic degradation of tetrathioarsenate were observed. In contrast to results from the laboratory, arsenite was oxidized by Thermocrinis in the field, potentially as a detoxification reaction. Comparing biotic and abiotic samples, bacterial transformation processes play an important role for differentiation of dissolved arsenic- and sulfur species.