Isolation of a Xanthobacter sp. degrading dichloromethane and characterization of the gene involved in the degradation.

A bacterial strain able to degrade dichloromethane (DCM) as the sole carbon source was isolated from a wastewater treatment plant receiving domestic and pharmaceutical effluent. 16S rDNA studies revealed the strain to be a Xanthobacter sp. (strain TM1). The new isolated strain when grown aerobically on DCM showed Luong type growth kinetics, with 1(max) of 0.094 h(-1) and S (m) of 1,435 mg l(-1). Strain TM1 was able to degrade other aromatic and aliphatic halogenated compounds, such as halobenzoates, 2-chloroethanol and dichloroethane. The gene for DCM dehalogenase, which is the key enzyme in DCM degradation, was amplified through PCR reactions. Strain TM1 contains type A DCM dehalogenase (dcmAa), while no product could be obtained for type B dehalogense (dcmAb). The sequence was compared against 12 dcmAa from other DCM degrading strains and 98% or 99% similarity was observed with all other previously isolated DCM dehalogenase genes. This is the first time a Xanthobacter sp. is reported to degrade DCM.

Biodegradation of 2-fluorobenzoate and dichloromethane under simultaneous and sequential alternating pollutant feeding.

Two up-flow fixed-bed reactors (UFBRs), inoculated with activated sludge and operated for 162 days, were fed 1mmolL(-1)d(-1) with two model halogenated compounds, 2-fluorobenzoate (2-FB) and dichloromethane (DCM). Expanded clay (EC) and granular activated carbon (GAC) were used as biofilm carrier. EC did not have any adsorption capacity for both model compounds tested, whereas GAC could adsorb 1.3mmolg(-1) GAC for 2-FB and 4.5mmolg(-1) GAC for DCM. Both pollutants were degraded in both reactors under simultaneous feeding. However, biodegradation in the EC reactor was more pronounced, and re-inoculation of the GAC reactor was required to initiate 2-FB degradation. Imposing sequential alternating pollutant (SAP) feeding caused starvation periods in the EC reactor, requiring time-consuming recovery of 2-FB biodegradation after resuming its feeding, whereas DCM degradation recovered significantly faster. The SAP feeding did not affect performance in the GAC reactor as biodegradation of both pollutants was continuously observed during SAP feeding, indicating the absence of true starvation.

Treatment of halogenated organic compounds and monitoring of microbial dynamics in up-flow fixed bed reactors under sequentially alternating pollutant scenarios.

Two up-flow fixed bed reactors (UFBR) were operated for 8 months treating a model synthetic wastewater containing 2-fluorobenzoate (2-FB) and dichloromethane (DCM). The stability of the reactors under dynamic conditions, that is, sequentially alternating pollutants (SAP), shock loads, and starvation periods was assessed. Two support materials were used: expanded clay (EC) that does not adsorb 2-FB or DCM, and granular-activated carbon (GAC) that adsorbs 180 mg g(-1) of 2-FB and 390 mg g(-1) of DCM. The reactors were inoculated with a 2-FB-degrading strain (FB2) and a DCM degrader (TM1). 2-FB was fed at organic loads ranging from 0 to 800 mg L(-1) d(-1), while DCM was fed at 0-250 mg L(-1) d(-1). 2-FB or DCM were never detected at the outlet of the GAC reactor, while in the EC reactor outlet small amounts were observed. Nevertheless, the highest biological elimination capacity was observed in the EC reactor (over 700 mg L(-1) d(-1) of 2-FB). DGGE analysis revealed a fairly stable bacterial community with the largest shifts occurring during starvation periods and changes in feed composition. Several bacterial strains isolated from the reactors showed capacity for 2-FB degradation, while only strain TM1 degraded DCM.