Draft Genome Sequence of a Propanotroph, Rhodococcus sp. Strain ENV425, Capable of Degrading Methyl tert-Butyl Ether and N-Nitrosodimethylamine

Biotransformation of PFAA Precursors by Oxygenase-Expressing Bacteria in AFFF-Impacted Groundwater and in Pure-Compound Studies with 6:2 FTS and EtFOSE

Numerous US drinking water aquifers have been contaminated with per- and polyfluoroalkyl substances (PFAS) from fire-fighting and fire-training activities using aqueous film-forming foam (AFFF). These sites often contain other organic compounds, such as fuel hydrocarbons and methane, which may serve as primary substrates for cometabolic (i.e., nongrowth-linked) biotransformation reactions. This work investigates the abilities of AFFF site relevant bacteria (methanotrophs, propanotrophs, octane, pentane, isobutane, toluene, and ammonia oxidizers), known to express oxygenase enzymes when degrading their primary substrates, to biotransform perfluoroalkyl acid (PFAA) precursors to terminal PFAAs. Microcosms containing AFFF-impacted groundwater, 6:2 fluorotelomer sulfonate (6:2 FTS), or N-ethylperfluorooctane sulfonamidoethanol (EtFOSE) were inoculated with the aerobic cultures above and incubated for 4 and 8 weeks at 22 °C. Bottles were sacrificed, extracted, and subjected to target, nontarget, and suspect screening for PFAS. The PFAA precursors 6:2 FTS, N-sulfopropyldimethyl ammoniopropyl perfluorohexane sulfonamide (SPrAmPr-FHxSA), and EtFOSE transformed up to 99, 71, and 93%, respectively, and relevant daughter products, such as the 6:1 fluorotelomer ketone sulfonate (6:1 FTKS), were identified in quantities previously not observed, implicating oxygenase enzymes. This is the first report of a suite of site relevant PFAA precursors being transformed in AFFF-impacted groundwater by bacteria grown on substrates known to induce specific oxygenase enzymes. The data provide crucial insights into the microbial transformation of these compounds in the subsurface.

Implementation of in situ aerobic cometabolism for groundwater treatment: State of the knowledge and important factors for field operation

In situ aerobic cometabolism of groundwater contaminants has been demonstrated to be a valuable bioremediation technology to treat many legacy and emerging contaminants in dilute plumes. Several well-designed and documented field studies have shown that this technology can concurrently treat multiple contaminants and reach very low cleanup goals. Fundamentally different from metabolism-based biodegradation of contaminants, microorganisms that cometabolically degrade contaminants do not obtain sufficient carbon and energy from the degradation process to support their growth and require an exogenous growth supporting primary substrate. Successful applications of aerobic cometabolic treatment therefore require special considerations beyond conventional in situ bioremediation, such as competitive inhibition between growth-supporting primary substrate(s) and contaminant non-growth substrates, toxic effects resulting from contaminant degradation, and differences in microbial population dynamics exhibited by biostimulated indigenous consortia versus bioaugmentation cultures. This article first provides a general review of microbiological factors that are likely to affect the rate of aerobic cometabolic biodegradation. We subsequently review fourteen well documented field-scale aerobic cometabolic bioremediation studies and summarize the underlying microbiological factors that may affect the performance observed in these field studies. The combination of microbiological and engineering principles gained from field testing leads to insights and recommendations on planning, design, and operation of an in situ aerobic cometabolic treatment system. With a vision of more aerobic cometabolic treatments being considered to tackle large, dilute plumes, we present several novel topics and future research directions that can potentially enhance technology development and foster success in implementing this technology for environmental restoration.

A multicomponent propane monooxygenase catalyzes the initial degradation of methyl tert-butyl ether in Mycobacterium vaccae JOB5

Methyl tert-butyl ether (MTBE) has been recognized as a groundwater contaminant due to its widespread distribution and potential threat to human health. The limited understanding of the enzymes catalyzing MTBE degradation restricts their application in MTBE bioremediation. In this study, an MTBE-degrading soluble di-iron monooxygenase that clusters phylogenetically with a known propane monooxygenase (PRM) encoded by the prmABCD gene cluster was identified and functionally characterized, revealing their role in MTBE metabolism by Mycobacterium vaccae JOB5. Transcriptome analysis demonstrated that the expression of prmABCD was upregulated when JOB5 was induced by MTBE. Escherichia coli Rosetta heterologously expressing prmABCD from JOB5 could transform MTBE, indicating that the PRM of JOB5 is capable of the initial degradation of MTBE. The loss of the gene encoding the oxygenase α-subunit or β-subunit, the coupling protein, or the reductase disrupted MTBE transformation by the recombinant E. coli Rosetta. In addition, the catalytic capacity of PRM is likely affected by residue G95 in the active site pocket and residues I84, P165, A269, and V270 in the substrate tunnel structure. Mutation of amino acids in the active site and substrate tunnel resulted in inefficiency or inactivation of MTBE degradation, and the activity in 1,4-dioxane (1,4-D) degradation was diminished less than that in MTBE degradation.IMPORTANCEMulticomponent monooxygenases catalyzing the initial hydroxylation of MTBE are important in MTBE biodegradation. Previous studies of MTBE degradation enzymes have focused on P450s, alkane monooxygenase and MTBE monooxygenase, but the vital role of soluble di-iron monooxygenases has rarely been reported. In this study, we deciphered the essential catalytic role of a PRM and revealed the key residues of the PRM in MTBE metabolism. Our findings provide new insight into the MTBE-degrading gene cluster and enzymes in bacteria. This characterization of the PRM associated with MTBE degradation expands our understanding of MTBE-degrading gene diversity and provides a novel candidate enzyme for the bioremediation of MTBE-contaminated sites.