The capacity of an aerobic bacterial strain to degrade several chlorinated aliphatic hydrocarbons (CAHs) via cometabolism was investigated. On the basis of the 16S rRNA gene sequencing analysis, the strain, provisionally called A, proved to be a Gram positive bacterium most closely related to members of the Genus Rhodococcus. Strain A proved capable to grow on the aliphatic hydrocarbons up to pentane, with the exception of methane. In resting-cell assays conducted in triplicate vials, it degraded vinyl chloride (VC) (studied concentration range: 0 – 165 μM), cis-1,2-dichloroethylene (cis-DCE) (0 – 390 μM), trans-1,2-dichloroethylene (0 – 1.4 μM), trichloroethylene (TCE) (0 – 0.7 μM), 1,1,2-trichloroethane (1,1,2-TCA) (0 – 190 μM) and chloroform (CF) (0 – 500 μM), but not 1,1,2,2-tetrachloroethane. The cometabolic transformation of these solvents was successfully interpolated with a Monod-type model comprising a term of biomass inactivation due to transformation product toxicity. The estimated maximum specific rates ranged between 1 μmol/(mg protein day) (for 1,1,2-TCA) and 11 μmol/(mg protein day) (for VC), whereas the estimated half-saturation constants varied between 49 μM (CF) to 96 μM (cis-DCE). Strain A proved significantly affected by CAH transformation product toxicity, with transformation capacities (a parameter defined as the amount of compound degraded per unit amount of cells inactivated) varying between 0.6 (for 1,1,2-TCA) and 3.1 (for CF) μmol CAH degraded / (mg protein inactivated). Propane inhibition on the transformation of both cis-DCE and CF proved significant and was successfully simulated with a model of competitive inhibition, whereas cis-DCE exerted a non-competitive inhibition on propane utilization. A strong mutual inhibition among the studied CAHs was also observed. Propane utilization and the degradation of cis-DCE and CF were strongly inactivated by the presence of acetylene (415 μM), indicating that these processes are mediated by a monooxygenase enzyme. The growth yield of strain A on propane proved equal to 0.16 mg protein / mg propane, and the endogenous decay coefficient to 0.005 1/day. In conclusion, the studied strain is potentially utilizable for the cometabolic biological treatment of wastewaters and groundwaters contaminated by mixtures of CAHs.
D. Frascari, E. Baleani, D. Pinelli, S. Fedi, D. Zannoni, M. Nocentini (2006). Chlorinated solvent biodegradation via aerobic cometabolism by a propane-grown Rhodococcus bacterial strain. s.l : s.n.
Chlorinated solvent biodegradation via aerobic cometabolism by a propane-grown Rhodococcus bacterial strain
FRASCARI, DARIO;BALEANI, EMILIA;PINELLI, DAVIDE;FEDI, STEFANO;ZANNONI, DAVIDE;NOCENTINI, MASSIMO
2006
Abstract
The capacity of an aerobic bacterial strain to degrade several chlorinated aliphatic hydrocarbons (CAHs) via cometabolism was investigated. On the basis of the 16S rRNA gene sequencing analysis, the strain, provisionally called A, proved to be a Gram positive bacterium most closely related to members of the Genus Rhodococcus. Strain A proved capable to grow on the aliphatic hydrocarbons up to pentane, with the exception of methane. In resting-cell assays conducted in triplicate vials, it degraded vinyl chloride (VC) (studied concentration range: 0 – 165 μM), cis-1,2-dichloroethylene (cis-DCE) (0 – 390 μM), trans-1,2-dichloroethylene (0 – 1.4 μM), trichloroethylene (TCE) (0 – 0.7 μM), 1,1,2-trichloroethane (1,1,2-TCA) (0 – 190 μM) and chloroform (CF) (0 – 500 μM), but not 1,1,2,2-tetrachloroethane. The cometabolic transformation of these solvents was successfully interpolated with a Monod-type model comprising a term of biomass inactivation due to transformation product toxicity. The estimated maximum specific rates ranged between 1 μmol/(mg protein day) (for 1,1,2-TCA) and 11 μmol/(mg protein day) (for VC), whereas the estimated half-saturation constants varied between 49 μM (CF) to 96 μM (cis-DCE). Strain A proved significantly affected by CAH transformation product toxicity, with transformation capacities (a parameter defined as the amount of compound degraded per unit amount of cells inactivated) varying between 0.6 (for 1,1,2-TCA) and 3.1 (for CF) μmol CAH degraded / (mg protein inactivated). Propane inhibition on the transformation of both cis-DCE and CF proved significant and was successfully simulated with a model of competitive inhibition, whereas cis-DCE exerted a non-competitive inhibition on propane utilization. A strong mutual inhibition among the studied CAHs was also observed. Propane utilization and the degradation of cis-DCE and CF were strongly inactivated by the presence of acetylene (415 μM), indicating that these processes are mediated by a monooxygenase enzyme. The growth yield of strain A on propane proved equal to 0.16 mg protein / mg propane, and the endogenous decay coefficient to 0.005 1/day. In conclusion, the studied strain is potentially utilizable for the cometabolic biological treatment of wastewaters and groundwaters contaminated by mixtures of CAHs.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
