Changzheng Cui

Removal of trace level amounts of twelve sulfonamides from drinking water by UV-activated peroxymonosulfate

Trace levels of residual antibiotics in drinking water may threaten public health and become a serious problem in modern society. In this work, we investigated the degradation of twelve sulfonamides (SAs) at environmentally relevant trace level concentrations by three different methods: ultraviolet (UV) photolysis, peroxymonosulfate (PMS) oxidation, and UV-activated PMS (UV/PMS). Sulfaguanidine, sulfadiazine, sulfamerazine, sulfamethazine, sulfathiazole, sulfamethoxydiazine, and sulfadimethoxine were be effectively removed by direct UV photolysis and PMS oxidation. However, sulfanilamide, sulfamethizole, sulfamethoxazole, sulfisoxazole, and sulfachloropyridazine were not completely degraded, despite prolonging the UV irradiation time to 30min or increasing the PMS concentration to 5.0mg·L-1. UV/PMS provided more thorough elimination of SAs, as demonstrated by the complete removal of 200ng·L-1 of all SAs within 5min at an initial PMS concentration of 1.0mg·L-1. UV/PMS promoted SA decomposition more efficiently than UV photolysis or PMS oxidation alone. Bicarbonate concentration and pH had a negligible effect on SA degradation by UV/PMS. However, humic acid retarded the process. Removal of 200ng·L-1 of each SA from a sample of sand-filtered effluent from a drinking water treatment plant (DWTPs) was quickly and completely achieved by UV/PMS. Meanwhile, about 41% of the total organic carbon (TOC) was eliminated. Scavenging experiments showed that sulfate radical (SO4-) was the predominant species involved in the degradation. It is concluded that UV/PMS is a rapid and efficient method for removing trace-level SAs from drinking water.

Development of a method for trace level determination of antibiotics in drinking water sources by high performance liquid chromatography-tandem mass spectrometry

The presence of antibiotics in drinking water sources is worthy of concern regarding their potentially harmful effects on drinking water quality. In this study, a sensitive and reliable method was developed for the detection of 14 antibiotics in drinking water sources based on solid phase extraction (SPE) and high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The primary parameters for the SPE procedure, including different SPE cartridges, pH value of the sample, extraction volume and washing conditions, were optimized to extract the analytes efficiently in a single step with improved recoveries. Chromatographic separation conditions and MS/MS parameters in multiple reaction monitoring (MRM) mode were optimized to improve the sensitivity and specificity of the method. The optimized method provided acceptable recoveries ranging from 60.5% to 103.3%. The validation study indicated that the method detection limits varied from 0.001 to 2.160 ng L−1 and the method quantification limits varied from 0.003 to 6.740 ng L−1. The precision of the method, expressed as relative standard deviation (RSD), ranged from 0.1% to 2.6% and from 0.3% to 3.8% for inter- and intra-day analyses, respectively. Assessment of matrix effects exhibited partial signal suppression from 1.2% to 28.7% for most analytes, but it indicated signal enhancement for tetracycline (15.2%) and oxytracycline (12.6%). The method was successfully applied to the determination of trace levels of antibiotics in drinking water sources in East China. Up to 13 antibiotics were detected at concentrations ranging from 0.16 to 147.05 ng L−1, and the primary antibiotic residues belonged to the groups of fluoroquinolones and tetracyclines.

Identification and Characterization of a Novel Gentisate 1,2-Dioxygenase Gene from a Halophilic Martelella Strain

Halophilic Martelella strain AD-3, isolated from highly saline petroleum-contaminated soil, can efficiently degrade polycyclic aromatic hydrocarbons (PAHs), such as phenanthrene and anthracene, in 3–5% salinity. Gentisic acid is a key intermediate in the microbial degradation of PAH compounds. However, there is little information on PAH degradation by moderately halophilic bacteria. In this study, a 1,077-bp long gene encoding gentisate 1,2-dioxygenase (GDO) from a halophilic Martelella strain AD-3 was cloned, sequenced, and expressed in Escherichia coli. The recombinant enzyme GDO was purified and characterized in detail. By using the 18O isotope experiment and LC-MS analysis, the sources of the two oxygen atoms added onto maleylpyruvate were identified as H2O and O2, respectively. The Km and kcat values for gentisic acid were determined to be 26.64 μM and 161.29 s−1, respectively. In addition, optimal GDO activity was observed at 30 °C, pH 7.0, and at 12% salinity. Site-directed mutagenesis demonstrated the importance of four highly conserved His residues at positions 155, 157, 167, and 169 for enzyme activity. This finding provides new insights into mechanism and variety of gentisate 1,2-dioxygenase for PAH degradation in high saline conditions.

Complete genome of Martelella sp. AD-3, a moderately halophilic polycyclic aromatic hydrocarbons-degrading bacterium.

Martelella sp. strain AD-3, a moderate halophilic bacterium, was isolated from a petroleum-contaminated soil with high salinity in China. Here, we report the complete genome of strain AD-3, which contains one circular chromosome and two circular plasmids. An array of genes related to metabolism of polycyclic aromatic hydrocarbons and halophilic mechanism in this bacterium was identified by the whole genome analysis.

Oxidation of antiepileptic drug oxcarbazepine stimulated by thermally activated persulfate

Oxcarbazepine (OXC) is widely used nowadays due to its similar therapeutic effects of carbamazepine (CBZ) but with fewer side effects. The prescribed consumption of OXC has increased significantly in some countries, and its environmental pollutions have become a major concern. This paper firstly reported the degradation of OXC by heat-activated persulfate. Effects of temperature, dosage of persulfate and pH on the oxidation of OXC were examined. OXC degradation followed a pseudo-first-order decay model. The rate of OXC oxidation rose with the increase of persulfate (2.0 mM to 6.0 mM) and pH (5.0 to 9.0). OXC can be oxidised almost completely within 10 min by persulfate (4.0 mM, pH 9.0, 50°C). HO was the major active free radical, 9-oxo-9, 10-dihydroacridine-4-carbaldehyde and 9, 10-dihydroacridine-9-carbaldehyde were the major intermediates of OXC degradation by heat-activated persulfate. The heat-activated persulfate demonstrating high potential for the degradation of OXC, is a promising technique for its removal.

Occurrence and removal of sulfonamide antibiotics and antibiotic resistance genes in conventional and advanced drinking water treatment processes

Sulfonamides (SAs) and sul antibiotic resistance genes (ARGs) have been extensively detected in drinking water sources and warrant further studies on the removal of them in different drinking water treatment processes (DWTPs). The prevalence of 13 SAs, sul1, sul2 and class I integrase gene intI1 in conventional and advanced processes was investigated using HPLC-MS/MS and real-time quantitative PCR (qPCR), respectively. The most abundant SA was sulfamethoxazole, with the maximum concentration of 67.27 ng/L. High concentration of sulfamethoxazole was also measured in finished water in both conventional (22.05 ng/L) and advanced (11.24 ng/L) processes. Overall, the removal efficiency of advanced process for each SA was higher than that of conventional process, except for sulfameter. The absolute concentrations of sul1, sul2 and intI1 in raw water ranged from 1.8 × 103 to 2.4 × 105 gene abundance/mL. After treatment, the residual sul ARGs and intI1 in finished water still remained at 102 - 104 gene abundance/mL. Conventional treatment units, including flocculation/sedimentation/sand filtration, played a more important role in removing sul1, sul2 and intI1 than oxidation (chlorination or ozonation) and granular activated carbon filtration treatments. Based on this work, more investigations are needed to help improve the removal of both antibiotics and ARGs in DWTPs.

Purification and Initial Characterization of 3-Hydroxybenzoate 6-Hydroxylase From a Halophilic Martelella Strain AD-3

3-Hydroxybenzoate 6-hydroxylase, an NADH-dependent flavoprotein, can convert 3-hydroxybenzoate which is an important intermediate in the biodegradation of many aromatic hydrocarbons. 3-Hydroxybenzoate is metabolized by entering the TCA cycle through the gentisate pathway. We found a putative 3HB6H gene from a cluster that potentially encodes for gentisic acid degradation from a halophilic Martelella sp. strain AD-3. The corresponding protein was expressed with an N-terminal His-tag and purified by Ni2+-nitrilotriacetic acid affinity chromatography. The protein showed an overexpressed band of about 46 kDa by SDS–PAGE, and it was also proven that the enzyme contains FAD by absorption spectroscopy and HPLC analysis. The optimal activity of 3HB6H from strain AD-3 was observed in phosphate buffer (pH 8.0) at 37°C without salinity (NaCl) and metal salts. The Km values of 3-hydroxybenzoate 6-hydroxylase were determined to be 72.6 ± 10.1 μM and 104.1 ± 18.2 μM for 400 μM NADH and 3-hydroxybenzoate, respectively. Site-directed mutagenesis showed that residues 305, 306 and 308 are important for FAD binding. In addition, we found that Tyr221 and Gln305 of 3HB6H from strain AD-3 are involved in substrate binding.