Differential Microbial Transformation of Nitrosamines by an Inducible Propane Monooxygenase

Abstract

The toxicity of N-nitrosamines, their presence in drinking and environmental water supplies, and poorly understood recalcitrance collectively necessitate a better understanding of their potential for bioattenuation. Here, we show that the bacterial strain Rhodococcus jostii RHA1 can biotransform N-nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA), N-nitrosopyrrolidine (NPYR), and possibly N-nitrosomorpholine (NMOR) in addition to N-nitrosodimethylamine (NDMA). Growth of cells on propane as the sole carbon source greatly enhanced degradation rates when contrasted with cells grown on complex organics. Propane-induced rates in order of fastest to slowest were NDMA > NDEA > NDPA > NPYR > NMOR at concentrations <2000 μg/L. Removal rates for linear functional groups scaled inversely with mass and cyclic nitrosamines were more recalcitrant than linear nitrosamines. Controls demonstrated significant NDEA and NDPA losses independent of biomass, suggesting abiotic processes may play a role in attenuation of these two compounds under experimental conditions tested here. In contrast to NDMA, a transition from first to zero order kinetics was not observed for the other nitrosamines included in this study over a concentration range of 20-2000 μg/L. A genetic knockout for the propane monooxygenase enzyme (PrMO) confirmed the role of this enzyme in the biotransformation of NDEA and NPYR. This study furthers our understanding of environmental nitrosamine attenuation by revealing an enzymatic mechanism for the biotransformation of multiple nitrosamines, their relative recalcitrance to transformation, and potential for abiotic loss.

Effect of advanced oxidation on N-nitrosodimethylamine (NDMA) formation and microbial ecology during pilot-scale biological activated carbon filtration

“…Biofiltration, wherein an absence of chemical disinfectant residual encourages biomass growth on the filter media, is emerging as an effective post-AOP polishing step for the removal of trace organic contaminants and assimiliable organics liberated during advanced oxidation to reduce baseline toxicity (Gerrity and Snyder, 2011;Reungoat et al, 2010 and. Specifically, biofiltration using biological activated carbon (BAC) has been shown to provide excellent removal of NDMA in recent studies (Farre et al, 2011;Hollender et al, 2009;Reungoat et al, 2010;Sundaram et al, 2014) and is consistent with microbial oxidation of this recalcitrant nitrosamine (Homme et al, 2013;Sharp et al, 2005Sharp et al, , 2007Sharp et al, and 2010. The high surface area of BAC and ability to sequester bioavailable substrates lends itself to colonization by a diverse microbial biofilm that can further contribute to water treatment through the metabolism of nutrients and organics.…”

Propane biostimulation in biologically activated carbon (BAC) selects for bacterial clades adept at degrading persistent water pollutants

“…8,9 While limited data exist on this subject for nitrosamines other than NDMA, Ho et al (2011) demonstrated signicant removal of NDMA, NDEA, and NMOR in laboratory-scale GAC lters during the rst few days of lter operation. Prior work on nitrosamine biodegradation has conrmed the role of a propane monooxygenase during attenuation by Rhodococcus jostii RHA1; 16,18 however, neither this genus nor relatives were present in the column experiments and no clear difference in the emergence of Actinomycetales were discerned as a function of propane biostimulation. While mineralogical and Fe(II)/Fe(III) characterization was not investigated, the presence of approximately 2.4 mg-Fe/g-BAC in our columns could also inuence this retention if present as reactive species.…”

“…Nitrosamine concentrations were analyzed by LC-MS/MS using prior published methods 16 and were collected in 1 day increments throughout the duration of the nitrosamine spike. A subsequent pulse with a new, discreet azide-killed control column (using archived Binney-derived BAC) that had not been conditioned with soluble organics was then conducted to determine if biological activity or the experimental progression of the columns inuenced nitrosamine retention.…”

“…For example, Xie and Zhou 4 found BAC to more effectively remove haloacetic acids as contrasted to an autoclaved control and therefore attributed this removal to biodegradation. Propane-utilizing microorganisms have been found capable of biodegrading multiple persistent water pollutants such as chlorinated solvents 12,13 and nitrosamines [14][15][16][17] in both pure culture and more ecologically diverse batch systems. 5 In addition to dissolved organic matter and associated disinfection byproducts, BAC can remove nutrients such ammonia 6 and other persistent and hazardous pollutants such as phthalate esters.…”

Fate of Environmental Pollutants

“…Removal rates for linear functional groups scaled inversely with mass and cyclic nitrosamines were more recalcitrant than linear nitrosamines. Controls demonstrated significant NDEA and NDPA losses independent of biomass, suggesting abiotic processes may play a role in attenuation of these two compounds under experimental conditions tested(Homme and Sharp, 2013).The attenuation of bulk organic matter and trace organic contaminants (TOrCs) was evaluated for various aquifer recharge and recovery (ARR)-ozone (O 3 ) hybrid treatment process combinations using soil-batch reactor and bench-scale ozonation experiments as a proof of concept prior to pilot and/or field studies. NDMA was eliminated below the method detection limit (<5 ng/L) both during ARR treatment alone and the ARR-ozone hybrid(Yoon, Drewes et al, 2013).Explosives.A study showed that aggressive TAML activator with peroxides boosts the effectiveness of the known surfactant/base promoted breakdown of 2,4,6trinitrotoluene (TNT) and transforms the surfactant induced nondestructive binding of base to 1,3,5-trinitrobenzene (TNB) into an extensive multistep degradation process.Treatment of basic cationic surfactant solutions of eitherTNT or TNB with TAML/peroxide (hydrogen peroxide and tert-butylhydroperoxide, TBHP) gave complete pollutant removal for both in less than 1 h with above 75% of the nitrogen and above 20% of the carbon converted to nitrite/nitrate and formate, respectively(Kundu et al, 2013) A novel highly photocatalytic graphene-ZnO-Au nanocomposites (G-ZnO-Au NCs) has been developed byRoy et al (2013) and used to reduce nitrobenzene.…”