Tetrachloroethene metabolism of Dehalospirillum multivorans

Abstract

Dehalospirillum multivorans is a strictly anaerobic bacterium that is able to dechlorinate tetrachloroethene (perchloroethylene; PCE) via trichloroethene (TCE) to cis-1,2-dichloroethene (DCE) as part of its energy metabolism. The present communication describes some features of the dechlorination reaction in growing cultures, cell suspensions, and cell extracts of D. multivorans. Cell suspensions catalyzed the reductive dechlorination of PCE with pyruvate as electron donor at specific rates of up to 150 nmol (chloride released) min-1 (mg cell protein)-1 (300 microM PCE initially, pH 7.5, 25 degrees C). The rate of dechlorination depended on the PCE concentration; concentrations higher than 300 microM inhibited dehalogenation. The temperature optimum was between 25 and 30 degrees C; the pH optimum at about 7.5. Dehalogenation was sensitive to potential alternative electron acceptors such as fumarate or sulfur; nitrate or sulfate had no significant effect on PCE reduction. Propyl iodide (50 microM) almost completely inhibited the dehalogenation of PCE in cell suspensions. Cell extracts mediated the dehalogenation of PCE and of TCE with reduced methyl viologen as the electron donor at specific rates of up to 0.5 mumol (chloride released) min-1 (mg protein).-1 An abiotic reductive dehalogenation could be excluded since cell extracts heated for 10 min at 95 degrees C were inactive. The PCE dehalogenase was recovered in the soluble cell fraction after ultracentrifugation. The enzyme was not inactivated by oxygen.

Use of Silicate Minerals for pH Control during Reductive Dechlorination of Chloroethenes in Batch Cultures of Different Microbial Consortia

“…Due to the higher mass of pollutant present, acidification is more likely to occur in the vicinity of the source zone of chlorinated ethenes (8,9). The tolerance of OHRB to low pH has been studied for pure cultures (10)(11)(12)(13)(14)(15)(16)(17)(18) and some consortia containing OHRB (19,20). It has been shown that OHRB are inactivated under acidic conditions (pH Ͻ5), and therefore, pH buffer amendments are required when the aquifer pH is Ͻ5 or when the soil buffering capacity is insufficient (3,9,21).…”

Analysis of acidity production during enhanced reductive dechlorination using a simplified reactive transport model

“…1). The first dataset combines the observations reported by Holliger et al [14] and Neumann et al [15], while the second includes results from Zhuang and Pavlostathis [22]. pH I > 0.5) at pH = 6, and a small amount of residual activity remains at pH = 4.…”

“…The metrics were normalized using the maximum value to facilitate the comparison. The solid line is the function assumed for the AAFB case, while the dashed line is the function fitted to the data from [22] and the dash-dot line is fitted to the data from [14] and [15]. The two behaviours observed in the laboratory experimental data result in significantly different behaviour in the field.…”

“…Several environmental factors are likely to influence the biomass sensitivity to pH; for example, the composition of the microbial consortium and other environmental variables (temperature, redox potential, availability of nutrients, etc.). It should also be noted that the three datasets, [14], [15] I could be more appropriate. The influence of the pH inhibition function used on the dechlorination extent is investigated in §4.…”

“…Low pH conditions are not optimal for microbial activity, and the highest microbial dechlorination rate is normally observed in the near-neutral pH range of 6.5-7.5 [6,[12][13][14][15].…”