The growing concern about antibiotic-resistant microorganisms has focused on the sludge from wastewater treatment plants (WWTPs) as a potential hotspot for their development and spread. To this end, it seems relevant to analyze the changes on the microbiota as a consequence of the antibiotics that wastewater may contain. This study aims at determining whether the presence of sulfamethoxazole (SMX), even in relatively low concentrations, modifies the microbial activities and the enzymatic expression of an activated sludge under aerobic heterotrophic conditions. For that purpose, we applied a metaproteomic approach in combination with genomic and transformation product analyses. SMX was biotransformed, and the metabolite 2,4(1H,3H)-pteridinedione-SMX (PtO-SMX) from the pterin-conjugation pathway was detected at all concentrations tested. Metaproteomics showed that SMX at 50−2000 μg/L slightly affected the microbial community structure, which was confirmed by DNA metabarcoding. Interestingly, an enhanced activity of the genus Corynebacterium and specifically of five enzymes involved in its central carbon metabolism was found at increased SMX concentrations. Our results suggest a role of Corynebacterium genus on SMX risks mitigation in our bioreactors.
Bacteria
of the genus Dehalogenimonas respire
with vicinally halogenated alkanes via dihaloelimination.
We aimed to describe involved proteins and their supermolecular organization.
Metagenomic sequencing of a Dehalogenimonas-containing culture resulted in a 1.65 Mbp draft genome of Dehalogenimonas alkenigignens strain BRE15M. It contained
31 full-length reductive dehalogenase homologous genes (rdhA), but only eight had cognate rdhB gene coding for
membrane-anchoring proteins. Shotgun proteomics of cells grown with
1,2-dichloropropane as an electron acceptor identified 1152 proteins
representing more than 60% of the total proteome. Ten RdhA proteins
were detected, including a DcpA ortholog, which was the strongest
expressed RdhA. Blue native gel electrophoresis
(BNE) demonstrating maximum activity was localized in a protein complex
of 146–242 kDa. Protein mass spectrometry revealed the presence
of DcpA, its membrane-anchoring protein DcpB, two hydrogen uptake
hydrogenase subunits (HupL and HupS), an iron–sulfur protein
(HupX), and subunits of a redox protein with a molybdopterin-binding
motif (OmeA and OmeB) in the complex. BNE after protein solubilization
with different detergent concentrations revealed no evidence for an
interaction between the putative respiratory electron input module
(HupLS) and the OmeA/OmeB/HupX module. All detected RdhAs comigrated
with the organohalide respiration complex. Based on genomic and proteomic
analysis, we propose quinone-independent respiration in Dehalogenimonas.
Many aquifers around the world are impacted by toxic chlorinated methanes derived from industrial processes due to accidental spills. Frequently, these contaminants co-occur with chlorinated ethenes and/or chlorinated benzenes in groundwater, forming complex mixtures that become very difficult to remediate. In this study, a multi-method approach was used to provide lines of evidence of natural attenuation processes and potential setbacks in the implementation of bioremediation strategies in multi-contaminated aquifers. First, this study determined i) the carbon and chlorine isotopic compositions (δ 13 C, δ 37 Cl) of several commercial pure phase chlorinated compounds, and ii) the chlorine isotopic fractionation (εCl =-5.2 ± 0.6‰) and the dual C-Cl isotope correlation (Λ C/Cl = 5.9 ± 0.3) during dichloromethane (DCM) degradation by a Dehalobacteriumcontaining culture. Such data provide valuable information for practitioners to support the interpretation of stable isotope analyses derived from polluted sites. Second, the bioremediation potential of two industrial sites contaminated with a mixture of organic pollutants (mainly DCM, chloroform (CF), trichloroethene (TCE), and monochlorobenzene (MCB)) was evaluated. Hydrochemistry, dual (C-Cl) isotope analyses, laboratory microcosms, and microbiological data were used to investigate the origin, fate and biodegradation potential of chlorinated methanes. At Site 1, δ 13 C and δ 37 Cl compositions from field samples were consistent with laboratory microcosms, which showed complete degradation of CF, DCM and TCE, while MCB remained.
Brominated organic compounds such as 1,2dibromoethane (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 organohaliderespiring bacteria (i.e., either Dehalococcoides or Dehalogenimonas). Different ε bulk C values (−1.8 ± 0.2 and −19.2 ± 3.5‰, respectively) were obtained, whereas their respective ε bulk Br values were lower and similar to each other (−1.22 ± 0.08 and −1.2 ± 0.5‰), leading to distinctly different trends (Λ C−Br = Δδ 13 C/Δδ 81 Br ≈ ε bulk C /ε bulk Br ) 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 (S N 2reaction). The strongly pathway-dependent Λ C−Br values illustrate the potential of this approach to elucidate the reaction mechanism of 1,2-DBA in the field and to select appropriate ε bulk C values for quantification of biodegradation. The results of this study provide valuable information for future biodegradation studies of 1,2-DBA in contaminated sites.
Dichloromethane (DCM, methylene chloride) is a toxic, high-volume industrial pollutant of long-standing. Anaerobic biodegradation is crucial for its removal from contaminated environments, yet prevailing mechanisms remain unresolved, especially concerning dehalogenation. In this study, we obtained an assembled genome of a novel DCM-degrading strain, Dehalobacterium formicoaceticum strain EZ94, from a stable DCM-degrading consortium, and we analyzed its proteome during degradation of DCM. A gene cluster recently predicted to play a major role in anaerobic DCM catabolism (the mec cassette) was found. Methyltransferases and other proteins encoded by the mec cassette were among the most abundant proteins produced, suggesting their involvement in DCM catabolism. Reductive dehalogenases were not detected. Genes and corresponding proteins for a complete Wood-Ljungdahl pathway, which could enable further metabolism of DCM carbon, were also found. Unlike for the anaerobic DCM degrader “Ca. F. warabiya,” no genes for metabolism of the quaternary amines choline and glycine betaine were identified. This work provides independent and supporting evidence that mec-associated methyltransferases are key to anaerobic DCM metabolism.
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