An Inducible Propane Monooxygenase Is Responsible for N -Nitrosodimethylamine Degradation by Rhodococcus sp. Strain RHA1 (original) (raw)
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Applied and Environmental Microbiology, 2007
Rhodococci are common soil heterotrophs that possess diverse functional enzymatic activities with economic and ecological significance. In this study, the correlation between gene expression and biological removal of the water contaminant N-nitrosodimethylamine (NDMA) is explored. NDMA is a hydrophilic, potent carcinogen that has gained recent notoriety due to its environmental persistence and emergence as a widespread micropollutant in the subsurface environment. In this study, we demonstrate that Rhodococcus sp. strain RHA1 can constitutively degrade NDMA and that activity toward this compound is enhanced by approximately 500-fold after growth on propane. Transcriptomic analysis of RHA1 and reverse transcriptase quantitative PCR assays demonstrate that growth on propane elicits the upregulation of gene clusters associated with (i) the oxidation of propane and (ii) the oxidation of substituted benzenes. Deletion mutagenesis of prmA, the gene encoding the large hydroxylase component of propane monooxygenase, abolished both growth on propane and removal of NDMA. These results demonstrate that propane monooxygenase is responsible for NDMA degradation by RHA1 and explain the enhanced cometabolic degradation of NDMA in the presence of propane.
Aerobic Biodegradation of N-Nitrosodimethylamine by the Propanotroph Rhodococcus ruber ENV425
Applied and Environmental Microbiology, 2009
The propanotroph Rhodococcus ruber ENV425 was observed to rapidly biodegrade N-nitrosodimethylamine (NDMA) after growth on propane, tryptic soy broth, or glucose. The key degradation intermediates were methylamine, nitric oxide, nitrite, nitrate, and formate. Small quantities of formaldehyde and dimethylamine were also detected. A denitrosation reaction, initiated by hydrogen atom abstraction from one of the two methyl groups, is hypothesized to result in the formation of n-methylformaldimine and nitric oxide, the former of which decomposes in water to methylamine and formaldehyde and the latter of which is then oxidized further to nitrite and then nitrate. Although the strain mineralized more than 60% of the carbon in [ 14 C]NDMA to 14 CO 2 , growth of strain ENV425 on NDMA as a sole carbon and energy source could not be confirmed. The bacterium was capable of utilizing NDMA, as well as the degradation intermediates methylamine and nitrate, as sources of nitrogen during growth on propane. In addition, ENV425 reduced environmentally relevant microgram/liter concentrations of NDMA to <2 ng/liter in batch cultures, suggesting that the bacterium may have applications for groundwater remediation.
Diversity of ‘benzenetriol dioxygenase’ involved in p -nitrophenol degradation in soil bacteria
Indian Journal of Microbiology, 2008
Ring hydroxylating dioxygenases (RHDOs) are one of the most important classes of enzymes featuring in the microbial metabolism of several xenobiotic aromatic compounds. One such RHDO is benzenetriol dioxygenase (BtD) which constitutes the metabolic machinery of microbial degradation of several mono- phenolic and biphenolic compounds including nitrophenols. Assessment of the natural diversity of benzenetriol dioxygenase (btd) gene sequence is of great significance from basic as well as applied study point of view. In the present study we have evaluated the gene sequence variations amongst the partial btd genes that were retrieved from microorganisms enriched for PNP degradation from pesticide contaminated agriculture soils. The gene sequence analysis was also supplemented with an in silico restriction digestion analysis. Furthermore, a phylogenetic analysis based on the deduced amino acid sequence(s) was performed wherein the evolutionary relatedness of BtD enzyme with similar aromatic dioxygenases was determined. The results obtained in this study indicated that this enzyme has probably undergone evolutionary divergence which largely corroborated with the taxonomic ranks of the host microorganisms.
Biodegradation, 2019
N-nitrosodimethylamine (NDMA) is a potential carcinogen that is produced as a disinfection by-product of chloramination or chlorination process in water and wastewater treatment systems. The ability of the dioxygenase-expressing bacteria, Rhodococcus sp. strain L4, to degrade NDMA after induction with cumene was examined in the presence and absence of its potential precursors. Dimethylamine (DMA), aniline (AN) and humic acid (HA) were selected as the precursors. The induced bacteria were able to degrade NDMA from initial concentrations ranging between 1 and 10 mg L-1 to an undetectable level (\ 0.24 lg L-1) while there was no degradation of NDMA by the corresponding non-induced strain. The specific first-order degradation rate of NDMA ranged from 0.337 to 0.426 lg g-protein-1 h-1. Successful removal of all precursors was achieved by the induced bacteria. The presence of DMA had no negative effect on NDMA degradation. In contrast, a lag period was observed for the degradation of NDMA when AN or HA was present (except for the presence of 0.1 mg L-1 AN). In the presence of all precursors, NDMA degradation was negatively affected by the increased concentration (from 1 to 10 mg L-1) of all precursors.
Journal of Bacteriology, 2008
Proteomics and targeted gene disruption were used to investigate the catabolism of benzene, styrene, biphenyl, and ethylbenzene in Rhodococcus jostii RHA1, a well-studied soil bacterium whose potent polychlorinated biphenyl (PCB)-transforming properties are partly due to the presence of the related Bph and Etb pathways. Of 151 identified proteins, 22 Bph/Etb proteins were among the most abundant in biphenyl-, ethylbenzene-, benzene-, and styrene-grown cells. Cells grown on biphenyl, ethylbenzene, or benzene contained both Bph and Etb enzymes and at least two sets of lower Bph pathway enzymes. By contrast, styrene-grown cells contained no Etb enzymes and only one set of lower Bph pathway enzymes. Gene disruption established that biphenyl dioxygenase (BPDO) was essential for growth of RHA1 on benzene or styrene but that ethylbenzene dioxygenase (EBDO) was not required for growth on any of the tested substrates. Moreover, whole-cell assays of the ⌬bphAa and etbAa1::cmrA etbAa2::aphII mutants demonstrated that while both dioxygenases preferentially transformed biphenyl, only BPDO transformed styrene. Deletion of pcaL of the -ketoadipate pathway disrupted growth on benzene but not other substrates. Thus, styrene and benzene are degraded via meta-and ortho-cleavage, respectively. Finally, catalases were more abundant during growth on nonpolar aromatic compounds than on aromatic acids. This suggests that the relaxed specificities of BPDO and EBDO that enable RHA1 to grow on a range of compounds come at the cost of increased uncoupling during the latter's initial transformation. The stress response may augment RHA1's ability to degrade PCBs and other pollutants that induce similar uncoupling.
Detection of genes for alkane and naphthalene catabolism in Rhodococcus sp. strain 1BN
Environmental Microbiology, 2000
Rhodococcus sp. 1BN was isolated from a contaminated site and showed various biodegradative capabilities. Besides naphthalene, strain 1BN degraded medium-(C 6 ) and long-chain alkanes (C 16 ±C 28 ), benzene and toluene, alone or when the hydrocarbons were mixed in equal proportions. The nucleotide sequence of an alk polymerase chain reaction (PCR) fragment revealed a 59% nucleotide homology to the Pseudomonas oleovorans alkB gene. The nar fragments were highly homologous to genes coding for large and small subunits of cis-naphthalene 1,2-dioxygenase (narAa and narAb) and to cis-naphthalene dihydrodiol dehydrogenase (narB) from other rhodococci. The oxidation of indene to cis-(1S,2R)-1,2dihydroxyindan by toluene-induced cells allows to hypothesize that strain 1BN also carries a toluene dioxygenase-like system.
Biotechnology and Bioengineering, 2010
Propane-induced cometabolic degradation of n-nitrosodimethylamine (NDMA) by two propanotrophs is characterized through kinetic, gene presence, and expression studies. After growth on propane, resting cells of Rhodococcus sp. RR1 possessed a maximum transformation rate (v max,n ) of 44 AE 5 mg NDMA (mg protein) À1 h À1 ; the rate for Mycobacterium vaccae (austroafricanum) JOB-5 was modestly lower with v max,n of 28 AE 3 mg NDMA (mg protein) À1 h À1 . Both strains were capable of degrading environmentally relevant, trace quantities of NDMA to below the experimental limit of detection, calculated as 20 ng NDMA L À1 . However, a comparison of half saturation constants (K s,n ) and NDMA degradation in the presence of propane revealed pronounced differences between the strains. The K s,n for strain RR1 was 36 AE 10 mg NDMA L À1 while the propane concentration needed to inhibit NDMA rates by 50% (K inh ) occurred at 7,700 mg propane L À1 (R 2 ¼ 0.9669). In contrast, strain JOB-5 had a markedly lower affinity for NDMA verses propane with a calculated K s,n of 2,200 AE 1,000 mg NDMA L À1 and K inh of 120 mg propane L À1 (R 2 ¼ 0.9895). Genomic and transcriptional investigations indicated that the functional enzymes involved in NDMA degradation and propane metabolism are different for each strain. For Rhodococcus sp. RR1, a putative propane monooxygenase (PrMO) was identified and implicated in NDMA oxidation. In contrast, JOB-5 was not found to possess a PrMO homologue and two functionally analogous alkane monoxygenases (AlkMOs) were not induced by growth on propane. Differences between the PrMO in this Rhodococcus and the unidentified enzyme(s) in the Mycobacterium may explain differences in NDMA degradation and inhibition kinetics between these strains.
Current Genomics, 2020
Background: Petroleum polycyclic aromatic hydrocarbons (PAHs) are known to be toxic and carcinogenic for humans and their contamination of soils and water is of great environmental concern. Identification of the key microorganisms that play a role in pollutant degradation processes is relevant to the development of optimal in situ bioremediation strategies. Objective: Detection of the ability of Pseudomonas fluorescens AH-40 to consume phenanthrene as a sole carbon source and determining the variation in the concentration of both nahAC and C23O catabolic genes during 15 days of the incubation period. Methods: In the current study, a bacterial strain AH-40 was isolated from crude oil polluted soil by enrichment technique in mineral basal salts (MBS) medium supplemented with phenanthrene (PAH) as a sole carbon and energy source. The isolated strain was genetically identified based on 16S rDNA sequence analysis. The degradation of PAHs by this strain was confirmed by HPLC analysis. The...