Microbiological quality of roof tank water in an urban village in southeastern China

Urban villages are unique residential neighborhoods in urban areas in China. Roof tanks are their main form of water supply, and water quality deterioration might occur in this system because of poor hygienic conditions and maintenance. In this study, water samples were seasonally collected from an urban village to investigate the influence of roof tanks as an additional water storage device on the variation in the microbial community structure and pathogenic gene markers. Water stagnation in the roof tank induced significant decreases in chlorine(p < 0.05), residual chlorine was as low as 0.02 mg/L in spring. Propidium monoazide(PMA)-qPCR revealed a one-magnitude higher level of total viable bacterial concentration in roof tank water samples(2.14 ± 1.81 × 105gene copies/mL) than that in input water samples(3.57 ± 2.90 × 104gene copies/mL, p < 0.05), especially in spring and summer. In addition,pathogenic fungi, Mycobacterium spp., and Legionella spp. were frequently detected in the roof tanks. Terminal users might be exposed to higher microbial risk induced by high abundance of Legionella gene marker. Spearman’s rank correlation and redundancy analysis showed that residual chlorine was the driving force that promoted bacterial colonization and shaped the microbial community. It is worth noted that the sediment in the pipe will be agitated when the water supply is restored after the water outages, which can trigger an increase in turbidity and bacterial biomass. Overall, the findings provide practical suggestions for controlling microbiological health risks in roof tanks in urban villages.

WHIRLY1 recruits the histone deacetylase HDA15 repressing leaf senescence and flowering in Arabidopsis

Leaf senescence is controlled by a complex regulatory network in which robustness is ensured by the activity of transcription factors and epigenetic regulators.However,how these coordinate the process of leaf senescence remains poorly understood.We found that WHIRLY1 interacts with Histone Deacetylase(HDA)15,a Reduced Potassium Dependence3(RPD3)/HDA1-type HDA,by using green fluorescent protein-nanotrap-mass spectrum assays.The development-dependent interaction between WHIRLY1 and HDA15 was further confirmed by bimolecular fluorescence complementation assays and co-immunoprecipitation assays in Arabidopsis.Multi-omics genome-wide transcriptome and H3K9 acetylome enrichment analysis showed that HDA15 delays leaf senescence and flowering by repressing the expression of the positive regulators of leaf senescence and flowering,such as LOX2 and LARP1 C,and reducing H3K9 ac levels at these loci;WHIRLY1 and HDA15 co-target to the region near the transcription start site of a subset of nutrient recycling-related genes(e.g.,Glutathione S-transferases 10,non-coding RNA,and photosystem II protein D1 synthesizer attenuator PDIL1-2),as well as WRKY53 and ELF4,and co-repress their expression by removing H3K9 acetylation.Our study revealed a key transcription regulatory node of nutrient recycling and senescence-associated genes involved in leaf senescence and flowering via the recruitment of HDA15 by the single-stranded DNA/RNA-binding protein WHIRLY1.

Molecular analysis of long-term biofilm formation on PVC and cast iron surfaces in drinking water distribution system

To understand the impacts of different plumbing materials on long-term biofilm formation in water supply system, we analyzed microbial community compositions in the bulk water and biofilms on faucets with two different materials-polyvinyl chloride （PVC） and cast iron, which have been frequently used for more thanlO years. Pyrosequencing was employed to describe both bacterial and eukaryotic microbial compositions. Bacterial communities in the bulk water and biofilm samples were significantly different from each other. Specific bacterial populations colonized on the surface of different materials. Hyphomicrobia and corrosion associated bacteria, such as Acidithiobacillus spp., Aquabacterium spp., Limnobacter thiooxidans, and Thiocapsa spp., were the most dominant bacteria identified in the PVC and cast iron biofilms, respectively, suggesting that bacterial colonization on the material surfaces was selective. Mycobacteria and Legionella spp. were common potential pathogenic bacteria occurred in the biofilm samples, but their abundance was different in the two biofilm bacterial communities. In contrast, the biofilm samples showed more similar eukaryotic communities than the bulk water. Notably, potential pathogenic fungi, i.e., Aspergillus spp. and Candida parapsilosis, occurred in similar abundance in both biofilms. These results indicated that microbial community, especially bacterial composition was remarkably affected by the different pipe materials （PVC and cast iron）.

Low nutrient levels as drinking water conditions can reduce the fitness cost of efflux pump-mediated ciprofloxacin resistance in Pseudomonas aeruginosa

The long-term persistence of antibiotic resistance in the environment, especially in drinking water, is a public health concern. Expression of an efflux pump, an important mechanism of resistance to antibiotics, usually confers a fitness cost in bacteria. In this study, we aimed to determine why antibiotic resistance conferred by overexpression of an efflux pump persisted in low-nutrient environments(TOC < 10 mg/L) such as drinking and source water in which antibiotic selective pressure might be very low or even absent.Competition experiments between wild-type Pseudomonas aeruginosa and ciprofloxacinresistant mutants revealed that the fitness cost of ciprofloxacin resistance significantly decreased(p < 0.05) under low-nutrient(0.5 mg/L total organic carbon(TOC)) relative to high-nutrient(500 mg/L TOC) conditions. Mechanisms underlying this fitness cost were analyzed. The mexD gene expression in resistant bacteria(cip3 strain) was significantly lower(p < 0.05) in low-nutrient conditions, with 10 mg/L TOC((8.01 ± 0.82)-fold), than in high-nutrient conditions, with 500 mg/L TOC((48.89 ± 4.16)-fold). Moreover, rpoS gene expression in resistant bacteria((1.36 ± 0.13)-fold) was significantly lower(p < 0.05) than that in the wild-type strain((2.78 ± 0.29)-fold) under low-nutrient conditions(10 mg/L TOC),suggesting a growth advantage. Furthermore, the difference in metabolic activity between the two competing strains was significantly smaller(p < 0.05) in low-nutrient conditions(5 and 0.5 mg/L TOC). These results suggest that nutrient levels are a key factor in determining the persistence of antibiotic resistance conferred by efflux pumps in the natural environment with trace amounts or no antibiotics.

Biofiltration and disinfection codetermine the bacterial antibiotic resistome in drinking water:A review and meta-analysis

The bacterial antibiotic resistome(BAR)is one of the most serious contemporary medical challenges.The BAR problem in drinking water is receiving growing attention.In this study,we focused on the distribution,changes,and health risks of the BAR throughout the drinking water treatment system.We extracted the antibiotic resistance gene(ARG)data from recent publications and analyzed ARG profiles based on diversity,absolute abundance,and relative abundance.The absolute abundance of ARG was found to decrease with water treatment processes and was positively correlated with the abundance of 16S rRNA(r=0.963,/?<0.001),indicating that the reduction of ARG concentration was accompanied by decreasing biomass.Among treatment processes,biofiltration and chlorination were discovered to play important roles in shaping the bacterial antibiotic resistome.Chlorination exhibited positive effects in controlling the diversity of ARG,while biofiltration,especially granular activated carbon filtration,increased the diversity of ARG.Both biofiltration and chlorination altered the structure of the resistome by affecting relative ARG abundance.In addition,we analyzed the mechanism behind the impact of biofiltration and chlorination on the bacterial antibiotic resistome.By intercepting influent ARG-carrying bacteria,biofilters can enrich various ARGs and maintain ARGs in biofilm.Chlorination further selects bacteria co-resistant to chlorine and antibiotics.Finally,we proposed the BAR health risks caused by biofiltration and chlorination in water treatment.To reduce potential BAR risk in drinking water,membrane filtration technology and water boiling are recommended at the point of use.