Biology subjects

Mack, E. E.

Publications and source records attributed to Mack, E. E..

3 recordsLinked to original sources

bioRxiv2025

Dehalobacter converts 2,3-dichloroaniline to aniline via 2-chloroaniline in a methanogenic enrichment culture

12,3-dichloroaniline (2,3-DCA) has widespread use in chemical manufacturing and remains a persistent groundwater contaminant. To better understand the pathway and kinetics of its reductive dechlorination, we conducted a laboratory kinetic experiment using an anaerobic enrichment culture dominated by Dehalobacter. At an initial field-relevant concentration of 40 mg/L, complete and stoichiometric dechlorination of 2,3-DCA to aniline via 2-CA was achieved. The intermediates, 2-chloroaniline (2-CA) and 3-chloroaniline, were transiently formed in a ratio of 8:1. The growth yields of Dehalobacter on 2,3-DCA and 2-CA were 1.2 {+/-} 0.1 x 108 and 1.3 {+/-} 0.1 x 108 16S rRNA gene copies/mol chloride, respectively. The maximum specific growth rate for 2,3-DCA, max, was 0.18 {+/-} 0.03 day-{superscript 1} with a half-saturation constant, Ks, at 45 {+/-} 16 mg /L. The first-order decay constant for Dehalobacter when starved of chlorinated electron acceptors was estimated at 0.017 {+/-} 0.001 day-{superscript 1}. Lactate fermentation, acetogenesis from ethanol, syntrophic propionate oxidation, and hydrogenotrophic methanogenesis were observed during dechlorination. This work provides insights into the organohalide respiration of 2,3-DCA to aniline and advances the understanding of microbial interactions during anaerobic dechlorination. These results offer guidance for developing stable dechlorinating microbial ecosystems and key kinetic parameters for predictive modeling of groundwater 2,3-DCA fate and transport. 3 SynopsisThis study demonstrated stoichiometric dechlorination of 2,3-dichloroaniline to aniline, characterized syntrophic interactions in a mixed anaerobic dechlorinating culture, and determined growth yield, first-order decay and Monod constants for Dehalobacter. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/639126v3_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@5d59c4org.highwire.dtl.DTLVardef@b05a3aorg.highwire.dtl.DTLVardef@1f39f6borg.highwire.dtl.DTLVardef@1676753_HPS_FORMAT_FIGEXP M_FIG C_FIG Created in BioRender. Wang, S. (2025) https://BioRender.com/f47t993

microbiology↗

bioRxiv2025

Dehalobacter dechlorinates dichloroanilines and contributes to the natural attenuation of dichloronitrobenzenes at a complex industrial site

The potential for bioremediation of dichloroanilines (2,3- and 3,4-DCA) and dichloronitrobenzenes (3,4-, 2,5- and 2,3-DCNB) was investigated using inocula from an industrial site in northeast of Brazil. Anaerobic biotransformation of these chlorinated compounds was observed in microcosms simulating site conditions, particularly when electron donor was added. To disentangle specific transformation reactions, sub-cultures from active anaerobic microcosms were enriched with individual DCA or DCNB isomers. In these single-compound enrichment cultures, DCNB isomers were reduced to the corresponding DCA. Each DCA isomer was stoichiometrically dechlorinated to the corresponding monochloroaniline (CA) isomers. Further dechlorination of CA to aniline was noted. The reduction of DCNB to DCA was sustained by known fermenters and possibly Desulfitobacterium, while Dehalobacter was clearly responsible for dechlorination of DCAs. These findings helped to attribute function to microbial community data retrieved from field samples to inform the conceptual site model and enable identification of bioactive zones and rate-limiting conditions at a complex site. More generally, these data broaden the understanding of the metabolic repertoire of Dehalobacter and provide a model for incorporating microbial community data into site remediation efforts. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=116 SRC="FIGDIR/small/638192v2_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@1667948org.highwire.dtl.DTLVardef@a4a128org.highwire.dtl.DTLVardef@507067org.highwire.dtl.DTLVardef@103a155_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical AbstractC_FLOATNO C_FIG Short synopsis statementA diverse microbial community contributes to natural attenuation at a complex contaminated site. Notably, dichloroanilines produced by biologically-mediated nitroreduction of dichloronitrobenzenes were dechlorinated by Dehalobacter.

microbiology↗

bioRxiv2021

Global distribution of anaerobic dichloromethane degradation potential

Anthropogenic activities and natural processes release dichloromethane (DCM), a toxic chemical with substantial ozone-depleting capacity. Specialized anaerobic bacteria metabolize DCM; however, the genetic basis for this process has remained elusive. Comparative genomics of the three known anaerobic DCM-degrading bacterial species revealed a homologous gene cluster, designated the methylene chloride catabolism (mec) gene cassette, comprising eight to ten genes with predicted 79.6 - 99.7% amino acid identity. Functional annotation identified genes encoding a corrinoid-dependent methyltransferase system, and shotgun proteomics applied to two DCM-catabolizing cultures revealed high expression of proteins encoded on the mec gene cluster during anaerobic growth with DCM. In a DCM-contaminated groundwater plume, the abundance of mec genes strongly correlated with DCM concentrations (R2 = 0.71 - 0.85) indicating their value as process-specific bioremediation biomarkers. mec gene clusters were identified in metagenomes representing peat bogs, the deep subsurface, and marine ecosystems including oxygen minimum zones (OMZs), suggesting DCM turnover in diverse habitats. The broad distribution of anaerobic DCM catabolic potential suggests a relevant control function for emissions to the atmosphere, and a role for DCM as a microbial energy source in critical zone environments. The findings imply that the global DCM flux might be far greater than emission measurements suggest. ImportanceDichloromethane (DCM) is an increasing threat to stratospheric ozone with both anthropogenic and natural emission sources. Anaerobic bacterial metabolism of DCM has not yet been taken into consideration as a factor in the global DCM cycle. The discovery of the mec gene cassette associated with anaerobic bacterial DCM metabolism and its widespread distribution in environmental systems highlight a strong attenuation potential for DCM. Knowledge of the mec cassette offers new opportunities to delineate DCM sources, enables more robust estimates of DCM fluxes, supports refined DCM emission modeling and simulation of the stratospheric ozone layer, reveals a novel, ubiquitous C1 carbon metabolic system, and provides prognostic and diagnostic tools supporting bioremediation of groundwater aquifers impacted by DCM.

microbiology↗