Microbial degradation of typical amino acids and its impact on the formation of trihalomethanes, haloacetonitriles and haloacetamides during chlor(am)ination.

Nitrogenous disinfection by-products (N-DBPs) in chlorinated drinking water are receiving increasing attention due to their elevated toxicities. An effective strategy to control the formation of N-DBPs is to reduce their nitrogenous precursors (e.g., amino acids [AAs], believed to be the important N-DBP precursors) before disinfection. So far, little information is available about the effectiveness of conventional microbial degradation at controlling the formation of N-DBPs. In this study, the biodegradability of 20 AAs was investigated, and the impacts of microbial degradation for the selected 6 typical AAs on the formation of N-DBPs (haloacetonitriles and haloacetamides) and traditional carbonaceous DBP (chloroform) were investigated. The results indicated that glycine, arginine, aspartic acid, asparagine, alanine and serine were susceptible to biodegradation, and the formation potentials (FPs) of DBPs were remarkably reduced after biodegradation. The highest chloroform FP reduction rates from tryptophan and tyrosine were 85.4% and 56.2%, respectively. The FPs of dichloroacetonitrile and trichloroacetamide were also reduced after biodegradation of the all selected AA samples during chlor(am)ination. Dichloroacetamide FPs decreased continuously with incubation time during chlorination for phenylalanine, asparagine, aspartic acid, and the mixed AAs, and the highest reduction rates were 78.7%, 74.6%, 46.7% and 35.3% respectively. The results of integrated toxicity analysis indicated that the pre-treatment of microbial degradation significantly decreased the integrated toxicity of DBPs formed from AAs. Moreover, the microbial community analysis revealed that Proteobacteria was predominant at phylum level in the mixed AA sample, and the dominant genera were Acinetobacter and Pseudomonas. Proteobacteria may play an important role in controlling DBP precursor.

Metagenomic insights into the distribution of antibiotic resistome between the gut-associated environments and the pristine environments.

Antibiotic resistance genes (ARGs) in the environment are promoted by anthropogenic activities, which cause potential risks to human health. However, large-scale quantitative data on antibiotic resistome from the pristine and anthropogenic environments remains largely unexplored. Here, we used metagenome-wide analysis to investigate the share and divergence in ARG profiles and their potential bacterial hosts between the pristine and gut-associated environments. We found that the abundance of total ARGs in gut-associated environments was significantly higher than the pristine environments (P < 0.001). The mcr-1 and tetX, the genes resistant to the last resort antibiotics (colistin and tigecycline, respectively), were in high abundance (4.57 copies/Gb and 3.39 copies/Gb, respectively) in gut-associated environments, suggesting the ARG pollution caused by anthropogenic antibiotics. Metagenomic assembly-based host-tracking analysis identified Escherichia, Bacteroides, and Clostridium as the predominant bacterial hosts of ARGs in gut-associated environments, while Alteromonas, Vibrio, and Proteobacteria as the predominant bacterial hosts of ARGs in pristine environments. We first described the broad diversity of ARG hosts in different environments using metagenome-wide analysis. Our results revealed the heterogeneous distribution of ARGs and their hosts among different microbial niches in gut-associated environments and the pristine environments.

Draft genome sequence of an OXA-23, OXA-66, ADC-25 and TEM-1D co-producing Acinetobacter baumannii ST195 isolated from a patient with neonatal pneumonia in China.

OBJECTIVES: The rapid spread of multidrug-resistant (MDR) Acinetobacter baumannii poses a substantial threat for morbidity and mortality worldwide. In particular, carbapenem-resistant A. baumannii has caused a severe challenge to human health. Here we reported the draft genome sequence of A. baumannii S131434, an OXA-23, OXA-66, ADC-25 and TEM-1D co-producing strain recovered from a patient with neonatal pneumonia in China and belonging to the globally disseminated sequence type 195 (ST195) of clonal complex 92 (CC92). METHODS: Genomic DNA was sequenced using an Illumina HiSeq platform and the reads were de novo assembled into contigs using CLC Genomics Workbench. The assembled contigs were annotated and bioinformatics analysis was performed. RESULTS: The genome comprised a circular chromosome of 3898344bp. The presence of the blaOXA-23, blaOXA-66, blaADC-25 and blaTEM-1D genes was detected. In addition, genes conferring resistance to aminoglycosides, macrolides and tetracycline were also identified. Antimicrobial susceptibility testing revealed that the isolate was resistant to all of the tested antibiotics except for polymyxin B, piperacillin/sulbactam and trimethoprim/sulfamethoxazole. CONCLUSION: To our knowledge, this is the first report of a clinical A. baumannii ST195 (CC92) isolate producing OXA-23, OXA-66, ADC-25 and TEM-1D in southern China. This draft genome will facilitate further our understanding of the antimicrobial resistance and pathogenic mechanisms in this strain and provides valuable information regarding the colonisation and adaptation of MDR pathogens.

The contribution of atmospheric particulate matter to the formation of CX3R-type disinfection by-products in rainwater during chlorination.

Atmospheric particulate matter (PM) can be scavenged by rainfall and contribute dissolved organic matter (DOM) to rainwater. Rainwater may serve as a part or the whole of drinking water sources, leading to the introduction of PM-derived DOM into drinking water. However, little information is available on the role of PM-derived DOM as a remarkable precursor of CX3R-type disinfection by-products (DBPs) in rainwater. In this study, samples were collected from ten occurrences of rainfall in Shanghai and batch experiments were executed to explore the contribution of PM-derived DOM to CX3R-type DBP formation in rainwater and to further understand some of unknowns regarding its characteristics. Results revealed that a part of PM was scavenged by rainfall and the scavenge performance was better for smaller PM. The formation potentials (FPs) of individual CX3R-type DBP were similar among size-isolated PM. TCM was predominant (around 0.5-4.5 µg-C/mg-C) and TCAA was the secondary (around 0.6-3.2 µg-C/mg-C) among all detectable CX3R-type DBPs. Based on the PM removal data and DBP FP results, the contribution of PM-derived DOM to CX3R-type DBP formation in rainwater was modeled. Furthermore, aromatic proteins and soluble microbial product-like compounds were found to be significant compositions, which were reported to be DBP precursors. And low molecular weight (< 10 kDa) DOM derived from total PM and rainwater exhibited higher CX3R-type DBP FPs. DOM fractions with higher SUVA254 and SUVA285 values gave relatively higher yields of CX3R-type DBPs, indicating that aromatic compounds played an important role in DBP formation.