Untersuchungen zum Einfluss von Redoxpotential und alternativen Elektronenakzeptoren als Umweltfaktoren auf die reduktive Dehalogenierung von Tetrachlorethen in Sulfurospirillum multivorans
Tetrachloroethene (PCE) is among the most ubiquitous contaminats in aquifers and is degradable to less chlorinated ethenes by microorganisms under reductive conditions. The anaerobic bacterium Sulfurospirillum multivorans can couple the reductive dechlorination of PCE to energy conversion via chemiosmotic mechanism (organohalid respiration). In this study the influence of different alternative electron acceptors and the redox potentials on the reductive dechlorination of PCE by S. multivorans was investigated. During the growth of S. multivorans the redox potential of the cultivation media changed and was, depending on the used substrates, adjusted to values between -250 mV and -50 mV. The redox potential of the medium was adjusted by the usage of redox active compounds and by potentiostat-controlled graphite electrodes. There was only a little impact on the dechlorination of PCE when the redox potential of the media was adjusted between +400 mV and -600 mV. It could be demonstrated that S. multivorans is able to grow in the presence of O2 in the gas phase of closed cultivation vessels and pyruvate as electron donor. The optimal growth was observed with 10 % O2 in the gas phase. During growth oxygen and pyruvate are consumed. This indicates, S. multivorans is a microaerobic organism. The dechlorination of PCE was not inhibited in the presence of the alternative electron acceptors fumarate, nitrate and oxygen, respectively, in combination with pyruvate as electron donor. During long term cultivation with different substrates in the absence of PCE or trichloroethene (TCE) the activity of the PCE dehalogenase (PceA) was lost attended with a loss of pceA gene expression and protein biosynthesis of PceA after more than 60 generations. However, the PCE dehalogenase in PceA depleded (PceA–) cells was inducible with PCE or TCE. It was shown that long-term cultivated cells still contain the functional pceA gene.