Dual C-Br Isotope Fractionation Indicates Distinct Reductive Dehalogenation Mechanisms of 1,2-Dibromoethane in Dehalococcoides- and Dehalogenimonas-Containing Cultures.

Brominated organic compounds such as 1,2-dibromoethane (1,2-DBA) are highly toxic groundwater contaminants. Multi-element compound-specific isotope analysis bears the potential to elucidate the biodegradation pathways of 1,2-DBA in the environment, which is crucial information to assess its fate in contaminated sites. This study investigates for the first time dual C-Br isotope fractionation during in vivo biodegradation of 1,2-DBA by two anaerobic enrichment cultures containing organohalide-respiring bacteria (i.e., either Dehalococcoides or Dehalogenimonas). Different εbulkC values (-1.8 ± 0.2 and -19.2 ± 3.5‰, respectively) were obtained, whereas their respective εbulkBr values were lower and similar to each other (-1.22 ± 0.08 and -1.2 ± 0.5‰), leading to distinctly different trends (ΛC-Br = Δδ13C/Δδ81Br ≈ εbulkC/εbulkBr) in a dual C-Br isotope plot (1.4 ± 0.2 and 12 ± 4, respectively). These results suggest the occurrence of different underlying reaction mechanisms during enzymatic 1,2-DBA transformation, that is, concerted dihaloelimination and nucleophilic substitution (SN2-reaction). The strongly pathway-dependent ΛC-Br values illustrate the potential of this approach to elucidate the reaction mechanism of 1,2-DBA in the field and to select appropriate εbulkC values for quantification of biodegradation. The results of this study provide valuable information for future biodegradation studies of 1,2-DBA in contaminated sites.

Dual carbon - chlorine isotope fractionation during dichloroelimination of 1,1,2-trichloroethane by an enrichment culture containing Dehalogenimonas sp.

Chlorinated ethanes are frequent groundwater contaminants but compound specific isotope analysis (CSIA) has been scarcely applied to investigate their degradation pathways. In this study, dual carbon and chlorine isotope fractionation was used to investigate for the first time the anoxic biodegradation of 1,1,2-trichloroethane (1,1,2-TCA) using a Dehalogenimonas-containing culture. The isotopic fractionation values obtained for the biodegradation of 1,1,2-TCA were ɛC = -6.9 ±â€¯0.4‰ and ɛCl = -2.7 ±â€¯0.3‰. The detection of vinyl chloride (VC) as unique byproduct and a closed carbon isotopic mass balance corroborated that dichloroelimination was the degradation pathway used by this strain. Combining the values of δ13C and δ37Cl resulted in a dual element C-Cl isotope slope of Λ = 2.5 ±â€¯0.2‰. Investigation of the apparent kinetic isotope effects (AKIEs) expected for cleavage of a CCl bond showed an important masking of the intrinsic isotope fractionation. Theoretical calculation of Λ suggested that dichloroelimination of 1,1,2-TCA was taking place via simultaneous cleavage of two CCl bonds (concerted reaction mechanism). The isotope data obtained in this study can be useful to monitor natural attenuation of 1,1,2-TCA via dichloroelimination and provide insights into the source and fate of VC in contaminated groundwaters.

Detoxification of 1,1,2-trichloroethane to ethene in a bioreactor co-culture of Dehalogenimonas and Dehalococcoides mccartyi strains.

1,1,2-Trichloroethane (1,1,2-TCA) is a non-flammable organic solvent and common environmental contaminant in groundwater. Organohalide-respiring bacteria are key microorganisms to remediate 1,1,2-TCA because they can gain metabolic energy during its dechlorination under anaerobic conditions. However, all current isolates produce hazardous end products such as vinyl chloride, monochloroethane or 1,2-dichloroethane that accumulate in the medium. Here, we constructed a syntrophic co-culture of Dehalogenimonas and Dehalococcoides mccartyi strains to achieve complete detoxification of 1,1,2-TCA to ethene. In this co-culture, Dehalogenimonas transformed 1,1,2-TCA via dihaloelimination to vinyl chloride, whereas Dehalococcoides reduced vinyl chloride via hydrogenolysis to ethene. Molasses, pyruvate, and lactate supported full dechlorination of 1,1,2-TCA in serum bottle co-cultures. Scale up of the cultivation to a 5-L bioreactor operating for 76d in fed-batch mode was successful with pyruvate as substrate. This synthetic combination of bacteria with known complementary metabolic capabilities demonstrates the potential environmental relevance of microbial cooperation to detoxify 1,1,2-TCA.

Molecular and carbon isotopic characterization of an anaerobic stable enrichment culture containing Dehalobacterium sp. during dichloromethane fermentation.

Biodegradation of dichloromethane (DCM) under reducing conditions is of major concern due to its widespread detection in contaminated groundwaters. Here, we report an anaerobic enrichment culture derived from a membrane bioreactor operating in an industrial wastewater treatment plant, capable of fermenting DCM and the brominated analogue dibromomethane (DBM). Comparative analysis of bacterial 16S rDNA-DGGE profiles from fresh liquid medium inoculated with single colonies picked from serial dilution-to-extinction agar vials showed that cultures degrading DCM contained a predominant band belonging to Dehalobacterium, however this band was absent in cultures unable to degrade DCM. Analysis of the microbial composition of the enrichment by bacterial 16S rRNA gene amplicon paired-end sequencing confirmed the presence of Dehalobacterium together with three additional phylotypes belonging to Acetobacterium, Desulfovibrio, and Wolinella, representing all four operational taxonomic units >99.9% of the retrieved sequences. The carbon isotopic fractionation (ε) determined for DCM degradation in this culture was -27±2‰. This value differs from the ε previously reported for the DCM-fermentative bacteria Dehalobacter (-15.5±1.5‰) but they are both significantly different from those reported for facultative methylotrophic organisms (ranging from -45 to -61‰). This significant difference in the ε allows differentiating between hydrolytic transformation of DCM via glutathione-dependent dehalogenases and fermentation pathway. CAPSULE: The carbon isotopic fractionation of dichloromethane by an enriched Dehalobacterium-containing culture has significant potential to monitor biodegradation of DCM in groundwaters.

Nonlinear process modeling of fructosyltransferase (FTase) using bootstrap re-sampling neural network model.

Recently, the increased demand of fructooligosaccharides (FOS) as a functional food has alarmed researchers to screen and identify new strains capable of producing fructosyltransferase (FTase). FTase is the enzyme that converts the substrate (sucrose) to glucose and fructose. The characterization of complex sugar such as table sugar, brown sugar, molasses, etc. will be carried out and the sugar that contained the highest sucrose concentration will be selected as a substrate. Eight species of macro-fungi will be screened for its ability to produce FTase and only one strain with the highest FTase activity will be selected for further studies. In this work, neural networks (NN) have been chosen to model the process based on their excellent 'resume' in coping with nonlinear process. Bootstrap re-sampling method has been utilized in re-sampling the data in this work. This method has successfully modeled the process as shown in the results.