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1.
Bell G 《The American naturalist》2000,155(5):606-617
2.
Ammonia- and Nitrite-Oxidizing Bacterial Communities in a Pilot-Scale Chloraminated Drinking Water Distribution System 总被引:5,自引:1,他引:4
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Nitrification in drinking water distribution systems is a common operational problem for many utilities that use chloramines for secondary disinfection. The diversity of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in the distribution systems of a pilot-scale chloraminated drinking water treatment system was characterized using terminal restriction fragment length polymorphism (T-RFLP) analysis and 16S rRNA gene (ribosomal DNA [rDNA]) cloning and sequencing. For ammonia oxidizers, 16S rDNA-targeted T-RFLP indicated the presence of Nitrosomonas in each of the distribution systems, with a considerably smaller peak attributable to Nitrosospira-like AOB. Sequences of AOB amplification products aligned within the Nitrosomonas oligotropha cluster and were closely related to N. oligotropha and Nitrosomonas ureae. The nitrite-oxidizing communities were comprised primarily of Nitrospira, although Nitrobacter was detected in some samples. These results suggest a possible selection of AOB related to N. oligotropha and N. ureae in chloraminated systems and demonstrate the presence of NOB, indicating a biological mechanism for nitrite loss that contributes to a reduction in nitrite-associated chloramine decay. 相似文献
3.
Long-Term Succession of Structure and Diversity of a Biofilm Formed in a Model Drinking Water Distribution System 总被引:6,自引:1,他引:5
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Adam C. Martiny Thomas M. Jrgensen Hans-Jrgen Albrechtsen Erik Arvin Sren Molin 《Applied microbiology》2003,69(11):6899-6907
In this study, we examined the long-term development of the overall structural morphology and community composition of a biofilm formed in a model drinking water distribution system with biofilms from 1 day to 3 years old. Visualization and subsequent quantification showed how the biofilm developed from an initial attachment of single cells through the formation of independent microcolonies reaching 30 μm in thickness to a final looser structure with an average thickness of 14.1 μm and covering 76% of the surface. An analysis of the community composition by use of terminal restriction fragment length polymorphisms showed a correlation between the population profile and the age of the sample, separating the samples into young (1 to 94 days) and old (571 to 1,093 days) biofilms, whereas a limited spatial variation in the biofilm was observed. A more detailed analysis with cloning and sequencing of 16S rRNA fragments illustrated how a wide variety of cells recruited from the bulk water initially attached and resulted in a species richness comparable to that in the water phase. This step was followed by the growth of a bacterium which was related to Nitrospira, which constituted 78% of the community by day 256, and which resulted in a reduction in the overall richness. After 500 days, the biofilm entered a stable population state, which was characterized by a greater richness of bacteria, including Nitrospira, Planctomyces, Acidobacterium, and Pseudomonas. The combination of different techniques illustrated the successional formation of a biofilm during a 3-year period in this model drinking water distribution system. 相似文献
4.
We surveyed the functional gene composition and diversity of microbial biofilm communities in 18 New Zealand streams affected by different types of catchment land use, using a comprehensive functional gene array, GeoChip 3.0. A total of 5,371 nutrient cycling and energy metabolism genes within 65 gene families were detected among all samples (342 to 2,666 genes per stream). Carbon cycling genes were most common, followed by nitrogen cycling genes, with smaller proportions of sulphur, phosphorus cycling and energy metabolism genes. Samples from urban and native forest streams had the most similar functional gene composition, while samples from exotic forest and rural streams exhibited the most variation. There were significant differences between nitrogen and sulphur cycling genes detected in native forest and urban samples compared to exotic forest and rural samples, attributed to contrasting proportions of nitrogen fixation, denitrification, and sulphur reduction genes. Most genes were detected only in one or a few samples, with only a small minority occurring in all samples. Nonetheless, 42 of 65 gene families occurred in every sample and overall proportions of gene families were similar among samples from contrasting streams. This suggests the existence of functional gene redundancy among different stream biofilm communities despite contrasting taxonomic composition. 相似文献
5.
Emilie Bruez Jessica Vallance Jonathan Gerbore Pascal Lecomte Jean-Pierre Da Costa Lucia Guerin-Dubrana Patrice Rey 《PloS one》2014,9(5)
Esca, a Grapevine Trunk Disease (GTD), is of major concern for viticulture worldwide. Our study compares the fungal communities that inhabit the wood tissues of vines that expressed or not foliar esca-symptoms. The trunk and rootstock tissues were apparently healthy, whether the 10 year-old plants were symptomatic or not. The only difference was in the cordon, which contained white rot, a typical form of esca, in 79% of symptomatic plants. Observations over a period of one year using a fingerprint method, Single Strand Conformation Polymorphism (SSCP), and the ITS-DNA sequencing of cultivable fungi, showed that shifts occurred in the fungal communities colonizing the healthy wood tissues. However, whatever the sampling time, spring, summer, autumn or winter, the fungi colonizing the healthy tissues of asymptomatic or symptomatic plants were not significantly different. Forty-eight genera were isolated, with species of Hypocreaceae and Botryosphaeriaceae being the most abundant species. Diverse fungal assemblages, made up of potentially plant-pathogenic and -protective fungi, colonized these non-necrotic tissues. Some fungi, possibly involved in GTD, inhabited the non-necrotic wood of young plants, but no increase in necrosis areas was observed over the one-year period. 相似文献
6.
Biofilms in Drinking Water Distribution Systems 总被引:1,自引:0,他引:1
Batté M. Appenzeller B.M.R. Grandjean D. Fass S. Gauthier V. Jorand F. Mathieu L. Boualam M. Saby S. Block J.C. 《Reviews in Environmental Science and Biotechnology》2003,2(2-4):147-168
Biofilms and loose deposits in drinking water distribution systems provide a mosaic of electrochemical and nutritive environments. Limiting biofilms requires a combination of actions with impact is relatively low as discussed in this article. 相似文献
7.
Renee J. Smith James S. Paterson Cally A. Sibley John L. Hutson James G. Mitchell 《PloS one》2015,10(6)
Drought events and the overexploitation of freshwater resources have led to the increased need to manage groundwater reserves. Aquifer storage and recovery (ASR), whereby artificial water is injected into aquifers for storage, is one of the proposed methods by which freshwater supplies can be increased. Microbial clogging following injection, however, is a major issue. Here, during laboratory simulations of ASR, we used flow cytometry and bar-coded pyrosequencing to investigate changes in microbial abundance and community dynamics. Bacterial abundance ranged from 5.0 × 104 to 1.4 × 107 cells ml-1 before the addition of synthetic wastewater. Following wastewater addition, a 25-fold decrease in abundance was observed, coinciding with a 12-fold increase in viral abundance. Taxa shifted from an overrepresentation of Sphingomonadales, Sphingobacteriales, Rhodospirillales, Caulobacterales, Legionellales, Bacillales, Fusobacteriales and Verrucomicrobiales prior to the addition of synthetic wastewater to Burkholderiales, Actinomycetales, Pseudomonadales, Xanthomonadales, Rhodobacterales, Thizobiales and Thiotrichales following the addition of synthetic wastewater. Furthermore, a significant difference in overall taxonomic composition between the groundwater samples before and after the addition of synthetic wastewater was observed, with water samples exhibiting more similarity to sediment samples after wastewater was added. Collectively, these results suggest that ASR may alter the taxonomic composition of endemic microbial communities and that complete profiles of groundwater properties, including microbial community abundance and composition need to be taken into consideration when selecting aquifers for ASR practices. 相似文献
8.
Katherine E. Fish Richard Collins Nicola H. Green Rebecca L. Sharpe Isabel Douterelo A. Mark Osborn Joby B. Boxall 《PloS one》2015,10(2)
Within drinking water distribution systems (DWDS), microorganisms form multi-species biofilms on internal pipe surfaces. A matrix of extracellular polymeric substances (EPS) is produced by the attached community and provides structure and stability for the biofilm. If the EPS adhesive strength deteriorates or is overcome by external shear forces, biofilm is mobilised into the water potentially leading to degradation of water quality. However, little is known about the EPS within DWDS biofilms or how this is influenced by community composition or environmental parameters, because of the complications in obtaining biofilm samples and the difficulties in analysing EPS. Additionally, although biofilms may contain various microbial groups, research commonly focuses solely upon bacteria. This research applies an EPS analysis method based upon fluorescent confocal laser scanning microscopy (CLSM) in combination with digital image analysis (DIA), to concurrently characterize cells and EPS (carbohydrates and proteins) within drinking water biofilms from a full-scale DWDS experimental pipe loop facility with representative hydraulic conditions. Application of the EPS analysis method, alongside DNA fingerprinting of bacterial, archaeal and fungal communities, was demonstrated for biofilms sampled from different positions around the pipeline, after 28 days growth within the DWDS experimental facility. The volume of EPS was 4.9 times greater than that of the cells within biofilms, with carbohydrates present as the dominant component. Additionally, the greatest proportion of EPS was located above that of the cells. Fungi and archaea were established as important components of the biofilm community, although bacteria were more diverse. Moreover, biofilms from different positions were similar with respect to community structure and the quantity, composition and three-dimensional distribution of cells and EPS, indicating that active colonisation of the pipe wall is an important driver in material accumulation within the DWDS. 相似文献
9.
A Technique To Quantify the Population Size and Composition of the Biofilm Component in Communities of Bacteria in the Phyllosphere 总被引:2,自引:3,他引:2
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The presence of microbial biofilms in the phyllosphere of terrestrial plants has recently been demonstrated, but few techniques to study biofilms associated with living plant tissues are available. Here we report a technique to estimate the proportion of the bacterial population on leaves that is assembled in biofilms and to quantitatively isolate bacteria from the biofilm and nonbiofilm (solitary) components of phyllosphere microbial communities. This technique is based on removal of bacteria from leaves by gentle washing, separation of biofilm and solitary bacteria by filtration, and disintegration of biofilms by ultrasonication. The filters used for this technique were evaluated for their nonspecific retention rates of solitary bacteria and for the efficiency of filtration for different concentrations of solitary bacteria in the presence of biofilms and other particles. The lethality and efficiency of disintegration of the sonication conditions used here were also evaluated. Isolation and quantification of bacteria by this technique is based on use of culture media. However, oligonucleotide probes, sera, or epifluorescent stains could also be used for direct characterization of the biofilm and solitary bacteria in the suspensions generated by this technique. Preliminary results from estimates of biofilm abundance in phyllosphere communities show that bacteria in biofilms constitute between about 10 and 40% of the total bacterial population on broad-leaf endive and parsley leaves. 相似文献
10.
11.
Fig trees (Ficus) are often ecologically significant keystone species because they sustain populations of the many seed-dispersing animals that feed on their fruits. They are prominent components of riparian zones where they may also contribute to bank stability as well as supporting associated animals. The diversity and distributions of riparian fig trees in deciduous and evergreen forests in Chiang Mai Province, Northern Thailand were investigated in 2010–2012. To record the diversity and abundance of riparian fig trees, we (1) calculated stem density, species richness, and diversity indices in 20×50 m randomly selected quadrats along four streams and (2) measured the distances of individual trees from four streams to determine if species exhibit distinct distribution patterns within riparian zones. A total of 1169 individuals (from c. 4 ha) were recorded in the quadrats, representing 33 Ficus species (13 monoecious and 20 dioecious) from six sub-genera and about 70% of all the species recorded from northern Thailand. All 33 species had at least some stems in close proximity to the streams, but they varied in their typical proximity, with F. squamosa Roxb. and F. ischnopoda Miq the most strictly stream-side species. The riparian forests in Northern Thailand support a rich diversity and high density of Ficus species and our results emphasise the importance of fig tree within the broader priorities of riparian area conservation. Plans to maintain or restore properly functioning riparian forests need to take into account their significance. 相似文献
12.
E. I. Sobolevskii 《Russian Journal of Marine Biology》2001,27(2):65-69
Seabirds were counted in September 1998 from the research vessel Professor Khromovand a motorboat in Pil'tun and Lunskii bays and in the contiguous areas of the eastern Sakhalin shelf. Data on the species composition, abundance, and distribution of seabirds are presented. A fairly high species diversity and significantly high density of seabirds were recorded in Pil'tun and Lunskii bays, which are the main areas where they concentrate during the summer months. 相似文献
13.
Composition and Dynamics of Bacterial Communities of a Drinking Water Supply System as Assessed by RNA- and DNA-Based 16S rRNA Gene Fingerprinting 总被引:1,自引:0,他引:1
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Stefan Eichler Richard Christen Claudia Hltje Petra Westphal Julia Btel Ingrid Brettar Arndt Mehling Manfred G. Hfle 《Applied microbiology》2006,72(3):1858-1872
14.
The purpose of a drinking water distribution system is to deliver drinking water to the consumer, preferably with the same quality as when it left the treatment plant. In this context, the maintenance of good microbiological quality is often referred to as biological stability, and the addition of sufficient chlorine residuals is regarded as one way to achieve this. The full-scale drinking water distribution system of Riga (Latvia) was investigated with respect to biological stability in chlorinated drinking water. Flow cytometric (FCM) intact cell concentrations, intracellular adenosine tri-phosphate (ATP), heterotrophic plate counts and residual chlorine measurements were performed to evaluate the drinking water quality and stability at 49 sampling points throughout the distribution network. Cell viability methods were compared and the importance of extracellular ATP measurements was examined as well. FCM intact cell concentrations varied from 5×103 cells mL−1 to 4.66×105 cells mL−1 in the network. While this parameter did not exceed 2.1×104 cells mL−1 in the effluent from any water treatment plant, 50% of all the network samples contained more than 1.06×105 cells mL−1. This indisputably demonstrates biological instability in this particular drinking water distribution system, which was ascribed to a loss of disinfectant residuals and concomitant bacterial growth. The study highlights the potential of using cultivation-independent methods for the assessment of chlorinated water samples. In addition, it underlines the complexity of full-scale drinking water distribution systems, and the resulting challenges to establish the causes of biological instability. 相似文献
15.
Chuanwu Xi Yongli Zhang Carl F. Marrs Wen Ye Carl Simon Betsy Foxman Jerome Nriagu 《Applied and environmental microbiology》2009,75(17):5714-5718
The occurrence and spread of antibiotic-resistant bacteria (ARB) are pressing public health problems worldwide, and aquatic ecosystems are a recognized reservoir for ARB. We used culture-dependent methods and quantitative molecular techniques to detect and quantify ARB and antibiotic resistance genes (ARGs) in source waters, drinking water treatment plants, and tap water from several cities in Michigan and Ohio. We found ARGs and heterotrophic ARB in all finished water and tap water tested, although the amounts were small. The quantities of most ARGs were greater in tap water than in finished water and source water. In general, the levels of bacteria were higher in source water than in tap water, and the levels of ARB were higher in tap water than in finished water, indicating that there was regrowth of bacteria in drinking water distribution systems. Elevated resistance to some antibiotics was observed during water treatment and in tap water. Water treatment might increase the antibiotic resistance of surviving bacteria, and water distribution systems may serve as an important reservoir for the spread of antibiotic resistance to opportunistic pathogens.The occurrence and spread of antibiotic-resistant bacteria (ARB) are pressing public health problems worldwide, and aquatic ecosystems are a recognized reservoir for ARB and antibiotic resistance genes (ARGs) (4, 6, 8, 11, 12, 15, 39). Naturally occurring ARB and ARGs in the aquatic environment are selected for and enriched for by antibiotics found in sewage and agricultural runoff, which result from the widespread and increased use of antibiotics (4, 11, 12, 15, 38). Historically, concerns about the microbial quality of drinking water have focused on the occurrence of pathogens in drinking water distribution systems (5, 34). However, the presence of trace levels of antibiotics and ARB in source water and finished drinking water may also greatly affect public health and is an emerging issue for the general public and the drinking water industry (3, 30). Although several studies have detected ARB in drinking water systems (2, 3, 20, 30, 38), most previous studies focused on cultivable bacteria and/or indicator organisms. Little is known about the fate of ARGs in drinking water systems, and it was recently proposed that ARGs are emerging contaminants (24).We used culture-dependent methods and molecular techniques to investigate the prevalence and dynamics of heterotrophic ARB and ARGs in a drinking water source (source RW-P) and treated drinking water (source DW-P) (see Materials and Methods in the supplemental material). We tested water from a drinking water plant located in Michigan and tap water from several small cities located in Michigan and Ohio (sources TW-1, TW-2, TW-3, and TW-4). Two independent samples were collected each time at each collection site at three different times, and we used four replicates from each sample for tests. We tested bacterial resistance to the following antibiotics: amoxicillin (amoxicilline), chloramphenicol, ciprofloxacin, gentamicin, rifampin (rifampicin), sulfisoxazole, and tetracycline. We also examined the presence of eight ARGs, including beta-lactam resistance genes (blaTEM and blaSHV), chloramphenicol resistance genes (cat and cmr), sulfonamide resistance genes (sulI and sulII), and tetracycline resistance genes (tetO and tetW).Total heterotrophic plate counts (HPC) were determined using R2A agar without added antibiotics. The water treatment process reduced the total HPC from 9.9 × 106 CFU/100 ml in source water to 68 CFU/100 ml in treated drinking water, indicating that there was efficient removal and/or deactivation of total HPC (Table (Table1).1). In contrast, the total 16S rRNA gene copy number decreased from 3.4 × 107 copies/100 ml in source water to 1.6 × 106 copies/100 ml in treated drinking water (Fig. (Fig.1).1). The discrepancy between the reduction in the HPC and the reduction in the total 16S rRNA gene copy number suggests that the final disinfection step effectively inactivated bacteria but most of the dead or damaged cells were still present in finished drinking water. The number of HPC in tap water ranged from 3.44 × 102 to 6.1 × 104 CFU/100 ml water, values that are lower than those for source water but significantly higher than those for treated drinking water, indicating that there is regrowth of bacteria in drinking water distribution systems. The copy numbers of total 16S rRNA genes in tap water ranged from 2.45 × 105 to 1.02 × 107 copies/100 ml water. The higher levels suggested by the 16S rRNA data are consistent with results of previous studies demonstrating that only 5 to 10% and 1% of bacteria in wastewater and soil, respectively, can be cultivated or identified by culture-based methods (9, 37). A significant correlation (P < 0.05, R2 = 0.78) was found between the 16S rRNA gene copy number and the total HPC if treated drinking water (DW-P) data were not included (Fig. (Fig.1).1). This suggests that cultivable bacteria in drinking water represent only a small portion of the total bacterial biomass. Including treated drinking water (DW-P) data resulted in a distorted correlation, suggesting that a large proportion of the 16S rRNA genes present came from dead and/or damaged cells. The levels of total heterotrophic bacteria were significantly higher in tap water (TW-1) than in treated drinking water (DW-P), indicating that there was bacterial regrowth in the water distribution system.Open in a separate windowFIG. 1.Heterotrophic bacteria and the 16S rRNA gene in different water samples. (A) Copy numbers of the 16S rRNA gene and numbers of heterotrophic bacteria (CFU) in 100 ml water. (B) Correlation (P < 0.05, R2 = 0.78) between the copy number of the 16S rRNA gene and the number of heterotrophic bacteria in different water samples (without the data for DW-P). RW-P, source water from the drinking water treatment plant; DW-P, finished drinking water from the drinking water treatment plant; TW-1, tap water from the city where the drinking water treatment plant is located; TW-2, TW-3, and TW-4, tap water from three towns in Michigan and Ohio close to the city where the TW-1 drinking water treatment plant is located. The statistical analysis was done using six samples for each type of water sample. Lg, log10.
Open in a separate windowaPrevalence was defined as the percentage of resistant HPC in the total HPC. The statistical analysis was done using six samples for each type and four technical replicates for each sample.bRW-P, source water from the drinking water treatment plant; DW-P, finished drinking water from the drinking water treatment plant; TW-1, tap water from the city where the drinking water treatment plant is located; TW-2, TW-3, and TW-4, tap water from three towns in Michigan and Ohio close to the city where the TW-1 drinking water treatment plant is located.cSignificantly different from RW-P.dSignificantly different from DW-P.The prevalence of HPC resistant to antibiotics was determined using R2A agar containing amoxicillin (4 mg/liter), chloramphenicol (16 mg/liter), ciprofloxacin (2 mg/liter), gentamicin (8 mg/liter), rifampin (2 mg/liter), sulfisoxazole (256 mg/liter), or tetracycline (8 mg/liter). Some groups of heterotrophic bacteria were resistant to all of the antibiotics at the concentrations tested in all water samples (Table (Table1).1). In the source water, 14.4% of the HPC were resistant to gentamicin and 1.7% were resistant to tetracycline. The resistance of HPC to amoxicillin, chloramphenicol, and rifampin was significantly higher (P < 0.01) in treated drinking water than in source water, while the resistance to sulfisoxazole was significantly lower (P < 0.01). Compared to treated drinking water (DW-P), the resistance of HPC to tetracycline in tap water was significantly greater and the resistance to amoxicillin was significantly lower (P < 0.01). The resistance to chloramphenicol and rifampin remained higher than the resistance in source water. The prevalence of HPC antibiotic resistance in tap water samples collected from other cities varied, but the resistance of HPC to rifampin was particularly high in all tap water samples.A number of previous studies have reported that ARB are common in drinking water (2, 3, 19, 25, 33). We added to these studies by testing water both before and after treatment, as well as tap water. Although the bacterial concentration was effectively lower during water treatment, the prevalence of resistance to amoxicillin, rifampin, and chloramphenicol nevertheless increased significantly.Several studies have discovered that chlorine, an agent widely used for disinfection, selects for ARB (2, 3, 9, 16, 33, 37). Armstrong et al. (2, 3) found that there was a significant increase in the proportion of multidrug-resistant (MAR) bacteria following flash mixing with chlorine. Murray et al. (16) demonstrated that the proportion of bacteria resistant to ampicillin and cephalothin (cefalotin) in sewage increased significantly following chlorination, and they observed a significant increase in the proportion of MAR strains during chlorination in laboratory experiments. Other studies demonstrated that the susceptibility of ARB to a disinfectant and the susceptibility of antibiotic-susceptible bacteria to a disinfectant are similar (7, 28), indicating that disinfection does not select ARB but instead induces the development of antibiotic resistance. Armstrong et al. (2, 3) suggested that stress-tolerant bacteria selected by chlorination might be more antibiotic resistant, and one study found that suboptimal chlorine treatment of drinking water selected for MAR Pseudomonas aeruginosa (33).The mechanism of chlorine-induced antibiotic resistance in bacteria is unknown. It is possible that chlorine can increase expression of the multidrug efflux pumps, leading to resistance to disinfection by-products as well as antibiotics. The drinking water treatment plant that we sampled used monochloramine as a disinfectant. No previous study has reported the effects of monochlroamine disinfection on ARB, but our results suggest that monochlromaine disinfection may have an effect similar to that of chlorine disinfection.Real-time PCR was used to quantify ARGs (including cat, cmr, blaTEM, blaSHV, sulI, sulII, tetW, and tetO) in collected water samples. All ARGs tested were detected in all water samples, except for the tetO and tetW genes, which were detected only in source water (Fig. (Fig.2).2). The copy number of each ARG in 100 ml water was calculated and normalized to the copy number of the total 16S rRNA genes to determine the relative abundance of each ARG in the water samples. Compared to the copy number in finished water, the copy number of ARGs in tap water was significantly greater (P < 0.001), except for the blaSHV gene, whose copy number was not significantly different (P = 0.124); the tetO and tetW genes were not detected in the drinking water sample after treatment. In terms of the relative abundance of ARGs in bacterial populations, all ARG/16S rRNA gene ratios were less than −3 log. Compared to source water, treated drinking water had a higher abundance of the cat and blaSHV genes (P < 0.001) but a lower abundance of the sulI gene (P < 0.001) (Fig. (Fig.2).2). No significant difference in any other ARG was found. After distribution, no significant change was observed in any ARG, except that the abundance of the blaTEM gene was significantly increased (P < 0.01) compared with the abundance in treated drinking water (DW-P) or in tap water (TW-1) (Fig. (Fig.2).2). The ARGs were also present in tap water samples collected from other cities. The similarity of the abundance of ARGs in the different tap water samples is quite remarkable (Fig. (Fig.2).2). The relative abundance of all ARGs was similar to that in the TW-1 tap water sample, except that the relative abundance of sulII and blaSHV was lower in the TW-2 and TW-3 tap water samples (Fig. (Fig.22).Open in a separate windowFIG. 2.Quantities of ARGs in different water samples. The bars indicate the copy numbers of the resistance genes normalized to the 16S rRNA gene copy number, and the symbols indicate the absolute copy numbers of ARGs in 100 ml water. RW-P, source water from the drinking water treatment plant; DW-P, finished drinking water from the drinking water treatment plant; TW-1, tap water from the city where the drinking water treatment plant is located; TW-2, TW-3, and TW-4, tap water from three towns in Michigan and Ohio close to the city where the TW-1 drinking water treatment plant is located. The statistical analysis was done using six samples for each type of water sample. Lg, log10.The quantities of individual ARGs were not significantly correlated with either HPC counts or 16S rRNA genes (data not shown), indicating that the ARGs tested were not evenly distributed among the bacterial populations in the water samples. However, the overall trends in quantity were similar for some ARGs and ARB. For example, in source water, treated drinking water, and tap water (TW-1), the number of heterotrophic bacteria resistant to amoxicillin, chloramphenicol, and sulfisoxazole corresponded to the proportion of genes coding for resistance to these antibiotics (blaSHV, cat, and sulI, respectively).Bacteria may inherit resistance to some antibiotics or can develop resistance via spontaneous mutation or the acquisition of resistant genes (35). The acquisition of a resistant gene via horizontal gene transfer is the most common and easiest way for bacteria to develop antibiotic resistance both in the environment and in a host (26, 29). Many bacteria transmit ARGs, and these ARGs were recently proposed to be emerging contaminants because of their widespread occurrence in aquatic ecosystems (13, 21, 22, 24). Plasmid-mediated blaTEM and blaSHV are the most common genes coding beta-lactamases and “extended-spectrum” beta-lactamases, a major cause of resistance to beta-lactams, and they are increasingly being found in different settings worldwide (14, 23). The enzymes encoded by these genes confer unequivocal resistance to ampicillin, amoxicillin, ticarillin, and carbenicillin (32, 36). We detected blaTEM and blaSHV genes in all but one water sample, which is evidence that these genes are distributed widely in drinking water systems. The selective increases in the levels of both genes in tap water due to either water treatment or regrowth within drinking water distribution systems suggest that the spread of at least some beta-lactam-resistant determinants may occur through drinking water distribution systems.Both tetO and tetW are tetracycline resistance genes encoding ribosomal protection proteins. Both of these genes are common in intestinal and rumen environments (1, 31); thus, their presence may indicate fecal contamination (22). If the tetO and tetW genes truly represent the level of fecal contamination, our results show that drinking water treatment was effective for eliminating and controlling fecal contamination.The most frequent cause of bacterial resistance to chloramphenicol is enzymatic inactivation by acetylation of the drug via different types of chloramphenicol acetyltransferases encoded by cat genes (17), but other mechanisms, such as efflux systems, may also contribute to chloramphenicol resistance (18). The proportion of cat genes increased significantly following water treatment, suggesting that the drinking water treatment did not effectively remove or inactivate the chloramphenicol-resistant bacterial population. On the other hand, the cmr gene, an efflux pump gene related to chloramphenicol resistance, showed little variation in different water sources.Sulfonamides act as competitive inhibitors of the enzyme dihydropteroate synthase in the folic acid pathway of bacterial and some eukaryotic cells. sulI and sulII encode alternative sulfonamide-resistant dihydropteroate synthases in gram-negative clinical bacteria, and both genes commonly occur (often at roughly the same frequency) in sulfisoxazole-resistant gram-negative clinical isolates (10). The drinking water treatment process significantly decreased the abundance of the sulI gene but had no significant influence on the sulII gene.In summary, we found heterotrophic ARB and ARGs in all finished water and tap water tested, although the amounts were small. The size of the general population of bacteria followed the order source water > tap water > finished water, indicating that there was regrowth of bacteria in drinking water distribution systems; elevated resistance to some antibiotics was observed during water treatment and in tap water. We show that the quantities of most ARGs are greater in tap water than in finished water and source water. The increased levels of ARGs and specialized groups of ARB in tap water compared to finished water and source water suggest that water treatment could increase the antibiotic resistance of surviving bacteria and/or induce transfer of ARGs among certain bacterial populations. Water distribution systems could serve as an incubator for growth of certain ARB populations and as an important reservoir for the spread of antibiotic resistance to opportunistic pathogens. Drinking water treatment processes and distribution systems can impact the spread of antibiotic resistance. Rusin et al. (27) estimated that the risk of infection by bacteria in drinking water was as low as 7.3 per billion people for exposure to low levels of Aeromonas and as high as 98 per 100 patients receiving antibiotic treatment exposed to high levels of Pseudomonas (27). Whether exposure to ARB results in an increased risk to the general public, particularly individuals with compromised immune systems, the very young, the very old, or individuals with chronic conditions, is not known and deserves further study. Future research should identify factors accounting for the selective increase in antibiotic resistance and develop new methods and approaches to reduce accumulation of such resistance. 相似文献
TABLE 1.
Prevalence of ARB HPC in source water, finished drinking water, and tap water from four townsaSampleb | Total HPC (CFU/100 ml) | % of total HPC resistant to:
| ||||||
---|---|---|---|---|---|---|---|---|
Amoxicillin | Ciprofloxacin | Chloramphenicol | Gentamicin | Rifampin | Sulfisoxazole | Tetracycline | ||
RW-P | 1.19 × 106 | 11.67 ± 4.39 | 11.60 ± 5.92 | 4.17 ± 1.93 | 14.42 ± 5.52 | 10.85 ± 3.57 | 7.46 ± 3.87 | 1.66 ± 0.80 |
DW-P | 68 | 39.55 ± 9.79c | 4.77 ± 4.71 | 19.45 ± 5.60c | 21.96 ± 14.43 | 47.98 ± 17.99c | 1.17 ± 1.14c | 1.50 ± 1.24 |
TW-1 | 1.6 × 104 | 15.22 ± 2.73d | 9.99 ± 4.76 | 13.96 ± 3.70c | 13.40 ± 1.73 | 62.00 ± 8.96c | 3.34 ± 1.21 | 3.78 ± 0.93c,d |
TW-2 | 6.04 × 104 | 3.02 ± 0.19 | 13.14 ± 0.48 | 5.49 ± 0.47 | 4.67 ± 0.21 | 28.10 ± 1.72 | 7.85 ± 0.67 | 0.08 ± 0.01 |
TW-3 | 3.44 × 102 | 4.07 ± 0.17 | 0.18 ± 0.07 | 0.75 ± 0.39 | 2.18 ± 0.62 | 82.15 ± 1.50 | 0.33 ± 0.03 | 0.98 ± 0.38 |
TW-4 | 2.46 × 103 | 14.33 ± 1.74 | 0.18 ± 0.05 | 2.05 ± 0.04 | 9.76 ± 0.34 | 14.23 ± 1.69 | 0.12 ± 0.001 | 0.04 ± 0.002 |
16.
17.
Yuan Liu Yongzhuo Liu Yuanjun Ding Jinwei Zheng Tong Zhou Genxing Pan David Crowley Lianqing Li Jufeng Zheng Xuhui Zhang Xinyan Yu Jiafang Wang 《PloS one》2014,9(7)
While microbial nitrogen transformations in soils had been known to be affected by heavy metal pollution, changes in abundance and community structure of the mediating microbial populations had been not yet well characterized in polluted rice soils. Here, by using the prevailing molecular fingerprinting and enzyme activity assays and comparisons to adjacent non-polluted soils, we examined changes in the abundance and activity of ammonia oxidizing and denitrifying communities of rice paddies in two sites with different metal accumulation situation under long-term pollution from metal mining and smelter activities. Potential nitrifying activity was significantly reduced in polluted paddies in both sites while potential denitrifying activity reduced only in the soils with high Cu accumulation up to 1300 mg kg−1. Copy numbers of amoA (AOA and AOB genes) were lower in both polluted paddies, following the trend with the enzyme assays, whereas that of nirK was not significantly affected. Analysis of the DGGE profiles revealed a shift in the community structure of AOA, and to a lesser extent, differences in the community structure of AOB and denitrifier between soils from the two sites with different pollution intensity and metal composition. All of the retrieved AOB sequences belonged to the genus Nitrosospira, among which species Cluster 4 appeared more sensitive to metal pollution. In contrast, nirK genes were widely distributed among different bacterial genera that were represented differentially between the polluted and unpolluted paddies. This could suggest either a possible non-specific target of the primers conventionally used in soil study or complex interactions between soil properties and metal contents on the observed community and activity changes, and thus on the N transformation in the polluted rice soils. 相似文献
18.
Composition and Metabolic Activities of Bacterial Biofilms Colonizing Food Residues in the Human Gut 总被引:5,自引:1,他引:4
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Bacteria growing in the human large intestine live in intimate association with the host and play an important role in host digestive processes, gut physiology, and metabolism. Fecal bacteria have been investigated extensively, but few studies have been done on biofilms that form on digestive wastes in the large bowel. The aims of this investigation were to investigate the composition and metabolic activities of bacterial communities that colonize the surfaces of food residues in fecal material, with respect to their role in the fermentation of complex carbohydrates. Fresh stools were obtained from 15 healthy donors, and food residues were separated by filtration. Adherent bacteria were removed by surfactant treatment for microbiological analysis and fermentation studies. Scanning electron microscopy and fluorescent in situ hybridization in conjunction with confocal laser scanning microscopy (CLSM) were used to visualize intact biofilms. Results showed that bacterial populations strongly adhering to particulate matter were phenotypically similar in composition to unattached communities, with bacteroides and bifidobacteria predominating. Biofilms comprised a mixture of living and dead bacteria, and CLSM showed that bifidobacteria in the biofilms occurred as isolated dispersed cells and in microcolonies near the interface with the substratum. Fermentation experiments with a variety of complex carbohydrates demonstrated that biofilm populations were more efficient in digesting polysaccharides, while nonadhering communities fermented oligosaccharides most rapidly. Acetate was the principal fermentation product formed by biofilm bacteria, whereas higher levels of butyrate were produced by nonadherent populations, showing that the two communities were metabolically distinct. 相似文献
19.
Understanding the consequences of fragmentation of coastal habitats is an important topic of discussion in marine ecology. Research on the effects of fragmentation has revealed complex and context-dependent biotic responses, which prevent generalizations across different habitats or study organisms. The effects of fragmentation in marine environments have been rarely investigated across heterogeneous habitats, since most studies have focused on a single type of habitat or patch. In this study, we assessed the effects of different levels of fragmentation (i.e. decreasing size of patches without overall habitat loss). We measured these effects using assemblages of macro-invertebrates colonizing representative morphological groups of intertidal macroalgae (e.g. encrusting, turf and canopy-forming algae). For this purpose, we constructed artificial assemblages with different combinations of morphological groups and increasing levels of fragmentation by manipulating the amount of bare rock or the spatial arrangement of different species in mixed assemblages. In general, our results showed that 1) fragmentation did not significantly affect the assemblages of macroinvertebrates; 2) at greater levels of fragmentation, there were greater numbers of species in mixed algal assemblages, suggesting that higher habitat complexity promotes species colonization. Our results suggest that predicting the consequences of fragmentation in heterogeneous habitats is dependent on the type and diversity of morphological groups making up those habitats. 相似文献
20.
Protozoan Bacterivory and Escherichia coli Survival in Drinking Water Distribution Systems 总被引:1,自引:0,他引:1
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The development of bacterial communities in drinking water distribution systems leads to a food chain which supports the growth of macroorganisms incompatible with water quality requirements and esthetics. Nevertheless, very few studies have examined the microbial communities in drinking water distribution systems and their trophic relationships. This study was done to quantify the microbial communities (especially bacteria and protozoa) and obtain direct and indirect proof of protozoan feeding on bacteria in two distribution networks, one of GAC water (i.e., water filtered on granular activated carbon) and the other of nanofiltered water. The nanofiltered water-supplied network contained no organisms larger than bacteria, either in the water phase (on average, 5 × 107 bacterial cells liter−1) or in the biofilm (on average, 7 × 106 bacterial cells cm−2). No protozoa were detected in the whole nanofiltered water-supplied network (water plus biofilm). In contrast, the GAC water-supplied network contained bacteria (on average, 3 × 108 cells liter−1 in water and 4 × 107 cells cm−2 in biofilm) and protozoa (on average, 105 cells liter−1 in water and 103 cells cm−2 in biofilm). The water contained mostly flagellates (93%), ciliates (1.8%), thecamoebae (1.6%), and naked amoebae (1.1%). The biofilm had only ciliates (52%) and thecamoebae (48%). Only the ciliates at the solid-liquid interface of the GAC water-supplied network had a measurable grazing activity in laboratory test (estimated at 2 bacteria per ciliate per h). Protozoan ingestion of bacteria was indirectly shown by adding Escherichia coli to the experimental distribution systems. Unexpectedly, E. coli was lost from the GAC water-supplied network more rapidly than from the nanofiltered water-supplied network, perhaps because of the grazing activity of protozoa in GAC water but not in nanofiltered water. Thus, the GAC water-supplied network contained a functional ecosystem with well-established and structured microbial communities, while the nanofiltered water-supplied system did not. The presence of protozoa in drinking water distribution systems must not be neglected because these populations may regulate the autochthonous and allochthonous bacterial populations. 相似文献