Untersuchungen zur Bioverfügbarkeit von Elementarschwefel und biogenem Schwefel und zur biotechnologischen Sulfidentfernung durch Grüne- und Purpurschwefelbakterien

Abstract

The following model organisms were used to study bioavailability of both elemental sulfur (SÃ °) and biologically produced sulfur (biogenic SÃ °) by anoxygenic phototrophic bacteria: Prosthecochloris vibrioformis (green sulfur bacterium), Allochromatium vinosum and A. vinosum mutant strain 21D. During photolithoautotrophic growth of P. vibrioformis with SÃ ° it could be observed that cells attached to the SÃ °-particles 24 h after the addition of the latter. The SÃ ° became hydrophilic, which was not attributed to abiotic reactions. If cells of P. vibrioformis were separated from SÃ ° by a dialysis membrane (exclusion size: 12-14 kDa), growth was not observed. If SÃ ° was added directly to the medium, growth of P. vibrioformis was dependent on the SÃ ° concentration in the medium. The protein pattern of extracellular enzymes from growth of P. vibrioformis with SÃ ° and sulfide was compared by SDS PAGE but no differences were observed. Furthermore, the protein pattern of whole cell proteins (WCP) from growth of P. vibrioformis with SÃ °, biogenic SÃ ° and sulfide, respectively, was compared. Two bands (ca. 38 kDa and ca. 40 kDa) were detected, which were only expressed during growth on SÃ ° and biogenic SÃ °, respectively.A. vinosum mutant strain 21D was used as a biocatalyst to remove sulfide from synthetic wastewater in a 5 L photobioreactor. The process type was semicontinuous with three fed-batch periods. Running time of the experiment was 1464 h. Due to a genetic modification in A. vinosum strain 21D, the formation of sulfate, which was unwanted in this process, and the attachment of biogenic SÃ ° on the glass wall, were circumvented.The average sulfide removal rate was 49.3 Ã µM/h and the maximal sulfide removal 98.7 %. An average sulfide removal of 91.7 % and an overall biogenic SÃ ° recycling of 60.4 % was achieved. By means of these results, it was shown that the use of A. vinosum 21D for sulfide elimination and recycling of biogenic SÃ ° is a competitive alternative to the currently dominating physicochemical methods.