François Jacob

Complete degradation of high concentrations of tetrachloroethylene by a methanogenic consortium in a fixed-bed reactor

Abstract Tetrachloroethylene (PCE) is a chlorinated aliphatic compound essentially used as a degreasing and dry-cleaning solvent. A methanogenic and sulfate-reducing consortium was obtained from anaerobic digested sludge from a waste water treatment plant (Bourg-en-Bresse, France). An ascending fixed-bed reactor inoculated with this mixed culture was fed semi-continuously with various PCE loading. The dechlorination of PCE was efficient and complete for high concentrations: 40–215 μM of PCE. Indeed, 215 μM PCE was degraded rapidly at the rate 3 μmol l−1 h−1 and with 98% PCE removal. No chlorinated products were accumulated in the effluent. The tracer experiments with 13C-labeled PCE indicated that the PCE was completely degraded to carbon in the biomass and CO2. The inhibitor of methanogenesis stopped the PCE dechlorination. Methanogens had a deciding role in the dechlorination process after the enrichment period with high concentration of PCE. To our knowledge, this is the first methanogenic consortium which dechlorinated with this capability. This fixed-bed reactor is an attractive method with high dechlorination rates, and the absence of chlorinated products, for removal of PCE in bioremediation processes.

Yeast production from crude sweet whey by a mixed culture ofCandida kefyr LY496 andCandida valida LY497.

SummaryThe conversion of crude sweet whey to single cell protein by a mixed culture of the yeastsCandida kefyr LY496 andCandida valida LY497 in non aseptic conditions was investigated. In comparison with single “pure culture” ofCandida kefyr LY496, ethanol accumulation during batch was prevented using the mixed culture. The efficiency of whey conversion to biomass was thus increased by as much as 20%.

Isolation of a methanogenic bacterium, Methanosarcina sp. strain FR, for its ability to degrade high concentrations of perchloroethylene

Tetrachloroethylene (PCE) is a toxic compound essentially used as a degreasing and dry-cleaning solvent. A methanogenic and sulfate-reducing consortium that dechlorinates and mineralizes high concentrations of PCE was derived from anaerobically digested sludge obtained from a waste water treatment plant (Bourg-en-Bresse, France). A methanogenic bacterium, strain FR, was isolated from this acclimated consortium. On the basis of morphological and physiological characteristics, strain FR was classified in the genus of Methanosarcina. Phylogeny analysis with the 16S rRNA gene sequence revealed that strain FR is highly related to Methanosarcina mazei and Methanosarcina frisia (99.6 and 99.5% identity, respectively). High concentrations (50-87 microM) of PCE were completely dechlorinated by strain FR cultures at the rate of 76 nM-mg protein(-1).day(-1). PCE dechlorination produced a nonidentified compound. The tracer experiments with [13C]PCE revealed that the product was nonchlorinated. Dechlorination of PCE to trichloroethylene was still active in the presence of boiled cell extract of the strain FR. However, no further dechlorination was observed. This result suggests that a cofactor rather than an enzymatic system is responsible for the first dechlorination of PCE. Dechlorination-active fractions purified from cell extracts on a XAD-4 column revealed the presence of F(420), F(430), and cobamides cofactors. This is the first report of the isolation of a methanogenic bacterium with the ability to dechlorinate high concentrations of PCE to a nonchlorinated product.