9,10-Phenanthrenedione biodegradation by a soil bacterium and identification of transformation products by LC/ESI-MS/MS

Assessment of bacterial biotransformation of alkylnaphthalene lubricating base oil component 1-butylnaphthalene by LC/ESI-MS(/MS)

Alkylnaphthalene lubricating oils are synthetic Group V base oils that are utilized in wide-ranging industrial applications and which are composed of polyalkyl chain-alkylated naphthalenes. Identification of alkylnaphthalene biotransformation products and determination of their mass spectrometry (MS) fragmentation signatures provides valuable information for predicting their environmental fates and for development of analytical methods to monitor their biodegradation. In this work, laboratory-based environmental petroleomics was applied to investigate the catabolism of the alkylnaphthalene, 1-butylnaphthalene (1-BN), by liquid chromatography electrospray ionization MS data mapping and targeted collision-induced dissociation (CID) analyses. Comparative mapping revealed that numerous catabolites were produced from soil bacterium, Sphingobium barthaii KK22. Targeted CID showed unique patterns of production of even-valued deprotonated fragments that were found to originate from specific classes of bacterial catabolites. Based upon results of CID analyses of catabolites and authentic standards, MS signatures were proposed to occur through formation of distonic radical anions from bacterially-produced alkylphenol biotransformation products. Finally, spectra interpretation was guided by CID results to propose chemical structures for twenty-two 1-BN catabolites resulting in construction of 1-BN biotransformation pathways. Multiple pathways were identified that included aromatic ring-opening, alkyl chain-shortening and production of α,β-unsaturated aldehydes from alkylated phenols. Until now, α,β-unsaturated aldehydes have not been a class of compounds much reported from alkylated polycyclic aromatic hydrocarbon (APAH) and PAH biotransformation. This work provides a new understanding of alkylnaphthalene biotransformation and proposes MS markers applicable to monitoring APAH biotransformation in the form of alkylated phenols, and by extension, α,β-unsaturated aldehydes, and toxic potential during spilled oil biodegradation.

Nondesulfurizing benzothiophene biotransformation to hetero and homodimeric ortho-substituted diaryl disulfides by the model PAH-degrading Sphingobium barthaii

Understanding the biotransformation mechanisms of toxic sulfur-containing polycyclic aromatic hydrocarbon (PASH) pollutants such as benzothiophene (BT) is useful for predicting their environmental fates. In the natural environment, nondesulfurizing hydrocarbon-degrading bacteria are major active contributors to PASH biodegradation at petroleum-contaminated sites; however, BT biotransformation pathways by this group of bacteria are less explored when compared to desulfurizing organisms. When a model nondesulfurizing polycyclic aromatic hydrocarbon-degrading soil bacterium, Sphingobium barthaii KK22, was investigated for its ability to cometabolically biotransform BT by quantitative and qualitative methods, BT was depleted from culture media but was biotransformed into mostly high molar mass (HMM) hetero and homodimeric ortho-substituted diaryl disulfides (diaryl disulfanes). HMM diaryl disulfides have not been reported as biotransformation products of BT. Chemical structures were proposed for the diaryl disulfides by comprehensive mass spectrometry analyses of the chromatographically separated products and were supported by the identification of transient upstream BT biotransformation products, which included benzenethiols. Thiophenic acid products were also identified, and pathways that described BT biotransformation and novel HMM diaryl disulfide formation were constructed. This work shows that nondesulfurizing hydrocarbon-degrading organisms produce HMM diaryl disulfides from low molar mass polyaromatic sulfur heterocycles, and this may be taken into consideration when predicting the environmental fates of BT pollutants.

Complete Genome Sequence of Sphingobium barthaii KK22, a High-Molecular-Weight Polycyclic Aromatic Hydrocarbon-Degrading Soil Bacterium

Sphingobium barthaii KK22^T is a high-molecular-weight polycyclic aromatic hydrocarbon-degrading soil bacterium that has been investigated in biotransformation, microbial ecology, and DNA damage studies. The complete genome sequence of S. barthaii revealed four closed circular sequences, including two chromosomes, a megaplasmid, and a smaller plasmid, by hybrid assembly using short- and long-read sequencing technologies.

Sphingobium barthaii KK22^T is a high-molecular-weight polycyclic aromatic hydrocarbon-degrading soil bacterium that has been investigated in biotransformation, microbial ecology, and DNA damage studies. The complete genome sequence of S. barthaii revealed four closed circular sequences, including two chromosomes, a megaplasmid, and a smaller plasmid, by hybrid assembly using short- and long-read sequencing technologies.

Selective removal of phenanthrene for the recovery of sodium dodecyl sulfate by UV-C and UV-C/PDS processes: Performance, mechanism and soil washing recycling

Soil washing is commonly used to remediate PAHs contaminated sites. However, the effluent after washing containing PAHs and surfactant may cause secondary pollution and remediation cost is still high, unless PAHs are selectively removed from the effluent and the surfactant is recovered and recycled. Herein, ultraviolet irradiation (254 nm, UV-C) and its combination with peroxydisulfate (UV-C/PDS) were applied to selectively degrade PHE in the synthetic soil washing effluent. At natural pH of 8.6, 98.2 % of PHE was removed within 30 min under 6 W UV-C irradiation. After adding 2 mM PDS, the time was shortened to 8 min but still achieving 98.7 % PHE removal and less toxic treated effluent than UV-C alone. The ¹O₂ was the main oxidizing species in UV-C alone system, while ¹O₂ as well OH and SO₄^- were responsible for PHE removal in the UV-C/PDS system. The possible intermediates of PHE degradation were recognized using liquid chromatography-mass spectrometry technique and the degradation pathways in both systems were proposed. Soil washing recycling experiments verified the recovered SDS could be reused directly without surfactant supplement and the soil washing efficiency changed insignificantly during three cycles. It indicates UV-C/PDS coupled with soil washing is a promising remediation technology.

Application of DNA adductomics to soil bacterium Sphingobium sp. strain KK22

Toward the development of ecotoxicology methods to investigate microbial markers of impacts of hydrocarbon processing activities, DNA adductomic analyses were conducted on a sphingomonad soil bacterium. From growing cells that were exposed or unexposed to acrolein, a commonly used biocide in hydraulic fracturing processes, DNA was extracted, digested to 2'-deoxynucleosides and analyzed by liquid chromatography-positive ionization electrospray-tandem mass spectrometry in selected reaction monitoring mode transmitting the [M + H](+) > [M + H - 116](+) transition over 100 transitions. Overall data shown as DNA adductome maps revealed numerous putative DNA adducts under both conditions with some occurring specifically for each condition. Adductomic analyses of triplicate samples indicated that elevated levels of some targeted putative adducts occurred in exposed cells. Two exposure-specific adducts were identified in exposed cells as 3-(2'-deoxyribosyl)-5,6,7,8-tetrahydro-6-hydroxy-(and 8-hydroxy-)pyrimido[1,2-a]- purine-(3H)-one (6- and 8-hydroxy-PdG) following synthesis of authentic standards of these compounds and subsequent analyses. A time course experiment showed that 6- and 8-hydroxy-PdG were detected in bacterial DNA within 30 min of acrolein exposure but were not detected in unexposed cells. This work demonstrated the first application of DNA adductomics to examine DNA damage in a bacterium and sets a foundation for future work.

Degradation of chiral neonicotinoid insecticide cycloxaprid in flooded and anoxic soil

Cycloxaprid (CYC), with two stereogenic centers from oxabridged ring, is a novel potent neonicotinoid insecticide. The investigation of relevant transformation products (TPs) is critical for the risk evaluation of CYC on environment impact and further regulatory decisions. In this study, stereoselective soil metabolism of CYC enantiomers was investigated using isotope labeling techniques. Liquid scintillation counting with LC-MS/MS was used to identify and quantify the major transformation products (TPs) of CYC enantiomers in four various soils under anoxic and flooded condition. Most of CYC had been transformed in four soils at 5d after treatment. Furthermore, CYC was found converted to a range of transformation products, which exhibited soil-specific dynamic changes. Cleavage of the oxabridged seven-member ring, reductive dechlorination in the chloropyridinyl and cleavage of C-N between the chloropyridinylmethyl and imidazalidine ring are the main transformation pathways of CYC. It is presumed that acidic condition may conduce to form the cleavage product of oxabridged seven-member ring. However, abiotic or biotic stereoselective persistence of TPs in all soils was not observed from the experimental data and may be attributed to the unstable oxabridged ring.