Xu-Xiang Zhang

Antibiotic resistance genes in water environment

The use of antibiotics may accelerate the development of antibiotic resistance genes (ARGs) and bacteria which shade health risks to humans and animals. The emerging of ARGs in the water environment is becoming an increasing worldwide concern. Hundreds of various ARGs encoding resistance to a broad range of antibiotics have been found in microorganisms distributed not only in hospital wastewaters and animal production wastewaters, but also in sewage, wastewater treatment plants, surface water, groundwater, and even in drinking water. This review summarizes recently published information on the types, distributions, and horizontal transfer of ARGs in various aquatic environments, as well as the molecular methods used to detect environmental ARGs, including specific and multiplex PCR (polymerase chain reaction), real-time PCR, DNA sequencing, and hybridization based techniques.

Metagenomic insights into chlorination effects on microbial antibiotic resistance in drinking water

This study aimed to investigate the chlorination effects on microbial antibiotic resistance in a drinking water treatment plant. Biochemical identification, 16S rRNA gene cloning and metagenomic analysis consistently indicated that Proteobacteria were the main antibiotic resistant bacteria (ARB) dominating in the drinking water and chlorine disinfection greatly affected microbial community structure. After chlorination, higher proportion of the surviving bacteria was resistant to chloramphenicol, trimethoprim and cephalothin. Quantitative real-time PCRs revealed that sulI had the highest abundance among the antibiotic resistance genes (ARGs) detected in the drinking water, followed by tetA and tetG. Chlorination caused enrichment of ampC, aphA2, bla(TEM-1), tetA, tetG, ermA and ermB, but sulI was considerably removed (p < 0.05). Metagenomic analysis confirmed that drinking water chlorination could concentrate various ARGs, as well as of plasmids, insertion sequences and integrons involved in horizontal transfer of the ARGs. Water pipeline transportation tended to reduce the abundance of most ARGs, but various ARB and ARGs were still present in the tap water, which deserves more public health concerns. The results highlighted prevalence of ARB and ARGs in chlorinated drinking water and this study might be technologically useful for detecting the ARGs in water environments.

Health risk assessment of polycyclic aromatic hydrocarbons in the source water and drinking water of China: Quantitative analysis based on published monitoring data

A carcinogenic risk assessment of polycyclic aromatic hydrocarbons (PAHs) in source water and drinking water of China was conducted using probabilistic techniques from a national perspective. The published monitoring data of PAHs were gathered and converted into BaP equivalent (BaP(eq)) concentrations. Based on the transformed data, comprehensive risk assessment was performed by considering different age groups and exposure pathways. Monte Carlo simulation and sensitivity analysis were applied to quantify uncertainties of risk estimation. The risk analysis indicated that, the risk values for children and teens were lower than the accepted value (1.00E-05), indicating no significant carcinogenic risk. The probability of risk values above 1.00E-05 was 5.8% and 6.7% for adults and lifetime groups, respectively. Overall, carcinogenic risks of PAHs in source water and drinking water of China were mostly accepted. However, specific regions, such as Yellow river of Lanzhou reach and Qiantang river should be paid more attention. Notwithstanding the uncertainties inherent in the risk assessment, this study is the first attempt to provide information on carcinogenic risk of PAHs in source water and drinking water of China, and might be useful for potential strategies of carcinogenic risk management and reduction.

Health risk from exposure of organic pollutants through drinking water consumption in Nanjing, China.

Human health risk analysis for 24 organic pollutants in drinking water of Nanjing was conducted. For non-carcinogenic risk, the 95th percentile hazard quotient (HQ) values of pollutants were all less than the unacceptable level of one. Considering the lifetime carcinogenic risk (LCR), however, the 95th percentile LCR values of 2,6-dinitrotoluene (1.30E-05), benzo(b)fluoranthene (3.10E-05), benzo(a)pyrene (3.37E-05) and dibenz(a,h)anthracene (2.09E-05) exceeded the unacceptable level of 1.00 E-05. These results suggest that organic pollutants in drinking water of Nanjing might pose potential lifetime carcinogenic risk for local consumers, and concerted efforts are required to ensure safety of consumers.

Abundance and diversity of bacterial nitrifiers and denitrifiers and their functional genes in tannery wastewater treatment plants revealed by high-throughput sequencing.

Biological nitrification/denitrification is frequently used to remove nitrogen from tannery wastewater containing high concentrations of ammonia. However, information is limited about the bacterial nitrifiers and denitrifiers and their functional genes in tannery wastewater treatment plants (WWTPs) due to the low-throughput of the previously used methods. In this study, 454 pyrosequencing and Illumina high-throughput sequencing, combined with molecular methods, were used to comprehensively characterize structures and functions of nitrification and denitrification bacterial communities in aerobic and anaerobic sludge of two full-scale tannery WWTPs. Pyrosequencing of 16S rRNA genes showed that Proteobacteria and Synergistetes dominated in the aerobic and anaerobic sludge, respectively. Ammonia-oxidizing bacteria (AOB) amoA gene cloning revealed that Nitrosomonas europaea dominated the ammonia-oxidizing community in the WWTPs. Metagenomic analysis showed that the denitrifiers mainly included the genera of Thauera, Paracoccus, Hyphomicrobium, Comamonas and Azoarcus, which may greatly contribute to the nitrogen removal in the two WWTPs. It is interesting that AOB and ammonia-oxidizing archaea had low abundance although both WWTPs demonstrated high ammonium removal efficiency. Good correlation between the qPCR and metagenomic analysis is observed for the quantification of functional genes amoA, nirK, nirS and nosZ, indicating that the metagenomic approach may be a promising method used to comprehensively investigate the abundance of functional genes of nitrifiers and denitrifiers in the environment.

Metagenomic analysis reveals significant changes of microbial compositions and protective functions during drinking water treatment

The metagenomic approach was applied to characterize variations of microbial structure and functions in raw (RW) and treated water (TW) in a drinking water treatment plant (DWTP) at Pearl River Delta, China. Microbial structure was significantly influenced by the treatment processes, shifting from Gammaproteobacteria and Betaproteobacteria in RW to Alphaproteobacteria in TW. Further functional analysis indicated the basic metabolic functions of microorganisms in TW did not vary considerably. However, protective functions, i.e. glutathione synthesis genes in ‘oxidative stress’ and ‘detoxification’ subsystems, significantly increased, revealing the surviving bacteria may have higher chlorine resistance. Similar results were also found in glutathione metabolism pathway, which identified the major reaction for glutathione synthesis and supported more genes for glutathione metabolism existed in TW. This metagenomic study largely enhanced our knowledge about the influences of treatment processes, especially chlorination, on bacterial community structure and protective functions (e.g. glutathione metabolism) in ecosystems of DWTPs.

Multivariate statistical study of organic pollutants in Nanjing reach of Yangtze River.

Multivariate statistical approach was used to identify the source apportionment of 25 semi-volatile compounds (SVOCs) in surface water in Nanjing reach of Yangtze River, China. Surface water samples were collected from six sites in January 2007. Concentrations of SVOCs were determined by gas chromatography equipped with a mass spectrometry detector (GC-MS). Cluster analysis (CA) and principal component analysis-multiple linear regression (PCA-MLR) were used for evaluation of contamination status, distribution and source apportionment. The results of CA showed that the six sites in this study could be divided into two significant groups, i.e. low and high pollutant groups. PCA-MLR results suggested that four source types were identified, explaining about 84.5% of the total variance. Of four sources, industrial and domestic sewage sources contributed 43.5-64.8% of various SVOCs in six sites, precipitance and runoff sources 4.22-42.87%, shipping sources 4.22-23.49%, and other miscellaneous sources 1.05-8.97%. These results indicated that point source pollutants affected the water quality of this region. High correlation coefficient (R(2)=0.973) between the measured and predicted concentrations of SVOCs suggested the applicability of the PCA-MLR for estimation of source contribution to the SVOCs in water.

Metagenomic Profiling of Antibiotic Resistance Genes and Mobile Genetic Elements in a Tannery Wastewater Treatment Plant

Antibiotics are often used to prevent sickness and improve production in animal agriculture, and the residues in animal bodies may enter tannery wastewater during leather production. This study aimed to use Illumina high-throughput sequencing to investigate the occurrence, diversity and abundance of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in aerobic and anaerobic sludge of a full-scale tannery wastewater treatment plant (WWTP). Metagenomic analysis showed that Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria dominated in the WWTP, but the relative abundance of archaea in anaerobic sludge was higher than in aerobic sludge. Sequencing reads from aerobic and anaerobic sludge revealed differences in the abundance of functional genes between both microbial communities. Genes coding for antibiotic resistance were identified in both communities. BLAST analysis against Antibiotic Resistance Genes Database (ARDB) further revealed that aerobic and anaerobic sludge contained various ARGs with high abundance, among which sulfonamide resistance gene sul1 had the highest abundance, occupying over 20% of the total ARGs reads. Tetracycline resistance genes (tet) were highly rich in the anaerobic sludge, among which tet33 had the highest abundance, but was absent in aerobic sludge. Over 70 types of insertion sequences were detected in each sludge sample, and class 1 integrase genes were prevalent in the WWTP. The results highlighted prevalence of ARGs and MGEs in tannery WWTPs, which may deserve more public health concerns.

Responses of mouse liver to dechlorane plus exposure by integrative transcriptomic and metabonomic studies.

Dechlorane plus (DP), a chlorinated flame retardant, has been widely detected in different environmental matrices and biota. However, toxicity data for DP have seldom been reported. In the present study, we investigated hepatic oxidative stress, DNA damage, and transcriptomic and metabonomic responses of male mice administered 500 mg/kg, 2000 mg/kg, and 5000 mg/kg of DP by gavage for 10 days. The results showed that DP exposure increased the level of superoxide dismutase (SOD) and 8-hydroxy-2-deoxyguanosine (8-OHdG). The microarray-based transcriptomic results demonstrated that DP exposure led to significant alteration of gene expression involved in carbohydrate, lipid, nucleotide, and energy metabolism, as well as signal transduction processes. The NMR-based metabonomic analyses corroborated these results showing changes of metabolites associated with the above altered mechanisms. Our results demonstrate that an oral exposure to DP can induce hepatic oxidative damage and perturbations of metabolism and signal transduction. These observations provide novel insight into toxicological effects and mechanisms of action of DP at the transcriptomic and metabonomic levels.

Characterization of tetracycline resistant bacterial community in saline activated sludge using batch stress incubation with high-throughput sequencing analysis

An innovative and cost-effective method, i.e., batch stress incubation with tetracycline in combination with Cloning-Sanger sequencing and Illumina high-throughput sequencing was developed to identify tetracycline resistant bacteria (TRB) in activated sludge (AS) treating saline sewage. This method overcomes the drawbacks of culture-based approach (unrepresentative and biased results) and utilizes both the advantages of Cloning-Sanger sequencing and Illumina high-throughput sequencing, that is, long length read for correct taxonomic assignment at lower ranks and enough sequencing depth for accurate quantification of TRB communities with medium to low abundances, respectively. High precision (relative deviation ≤ 16.1%) was obtained for all taxon ranks with relative abundances over 0.01%. In the AS sample, TRB consisted of 13 genera with Haliea, Microbacterium and Paracoccus as dominate genera and 6 new TRB genera, i.e., Haliea, Rheinheimera, Alishewanella, Idiomarina, Pseudorhodobacter and Algoriphagus. The increase of tetG and tetA abundance might be associated with the significant increase of Pseudomonas (tetG and tetA host) in the AS after tetracycline stress incubation. tetS abundance also showed an obvious increase after 20 mg/L tetracycline treatment. This method provided a new tool to screen other antibiotic resistant bacteria, bacteria resistant to heavy metals or disinfectants in AS samples.