Energiekonservierung über Organohalid-Respiration in Sulfurospirillum multivorans
The epsilonproteobacterium Sulfurospirillum multivorans is able to couple the reductive dechlorination of tetrachloroethene (PCE) to energy conservation via electron transport phosphorylation (organohalide respiration). The key enzyme of this anaerobic respiration is the reductive PCE dehalogenase (PceA). In this thesis, we investigated which proteins and possible other components (for example, quinones) are involved in the electron transfer between the enzymes, responsible for the oxidation of the electron donors, and PceA. In order to elucidate the PCE respiratory chain the genome of S. multivorans was sequenced and a differential proteome analysis was conducted. Involvement of quinones and a reverse electron flow were tested by inhibition studies and the quinones were identified. The experimental approaches allowed for the identification of proteins specifically produced in PCE-grown cells. Among other proteins, a quinol dehydrogenase (similar to NapGH found in nitrate respiration) was identified, which is presumably involved in electron transfer to PceA. Subsequently, the periplasmic, iron-sulfur cluster-containing component of the quinol dehydrogenase was heterologously expressed in Escherichia coli and purified. With quinone analogues, PCE respiration was inhibited, pointing to the involvement of quinones. In S. multivorans, organohalide respiration was blocked by protonophores while there was no effect of uncouplers on PCE-respiration of the gram-positive Desulfitobacterium hafniense Y51. The latter organism lacks NapGH-type quinol dehydrogenase genes. Until now, the microbial dechlorination of PCE has only be described under anaerobic conditions. In this study, the ability of the microaerobic organism S. multivorans to dechlorinate PCE in the presence of oxygen concentrations below 0.5% was demonstrated. The results of this study include key parameters for studies on reductive dehalogenation in oxic-anoxic zones of PCE-contaminated sites.