Influence of pipe materials on the microbial community in unchlorinated drinking water and biofilm

Effect of household pipe materials on formation and chlorine resistance of the early-stage biofilm: various interspecific interactions exhibited by the same microbial biofilm in different pipe materials

Microbial community biofilm exists in the household drinking water system and would pose threat to water quality. This paper explored biofilm formation and chlorination resistance of ten dual-species biofilms in three typical household pipes (stainless steel (SS), polypropylene random (PPR), and copper), and investigated the role of interspecific interaction. Biofilm biomass was lowest in copper pipes and highest in PPR pipes. A synergistic or neutralistic relationship between bacteria was evident in most biofilms formed in SS pipes, whereas four groups displayed a competitive relationship in biofilms formed in copper pipe. Chlorine resistance of biofilms was better in SS pipes and worse in copper pipes. It may be helped by interspecific relationships, but was more dependent on bacteria and resistance mechanisms such as more stable extracellular polymeric substance. The corrosion sites may also protect bacteria from chlorination. The findings provide useful insights for microbial control strategies in household drinking water systems.

Influence of drinking water biofilm microbiome on water quality: Insights from a real-scale distribution system

Biofilms, constituting over 95 % of the biomass in drinking water distribution systems, form an ecosystem impacting both the aesthetic and microbiological quality of water. This study investigates the microbiome of biofilms within a real-scale drinking water distribution system in eastern Spain, utilizing amplicon-based metagenomics. Forty-one biofilm samples underwent processing and sequencing to analyze both bacterial and eukaryotic microbiomes, with an assessment of active biomass. Genus-level analysis revealed considerable heterogeneity, with Desulfovibrio, Ralstonia, Bradyrhizobium, Methylocystis, and Bacillus identified as predominant genera. Notably, bacteria associated with corrosion processes, including Desulfovibrio, Sulfuricella, Hyphomicrobium, and Methylobacterium, were prevalent. Potentially pathogenic bacteria such as Helicobacter, Pseudomonas, and Legionella were also detected. Among protozoa, Opisthokonta and Archaeplastida were the most abundant groups in biofilm samples, with potential pathogenic eukaryotes (Acanthamoeba, Naegleria, Blastocystis) identified. Interestingly, no direct correlation between microbiota composition and pipe materials was observed. The study suggests that the usual concentration of free chlorine in bulk water proved insufficient to prevent the presence of undesirable bacteria and protozoa in biofilms, which exhibited a high concentration of active biomass.

Growth dynamic of biofilm-associated Naegleria fowleri in freshwater on various materials

In industrial water systems, the occurrence of biofilm-associated pathogenic free-living amoebae (FLA) such as Naegleria fowleri is a potential hygienic problem, and factors associated with its occurrence remain poorly understood. This study aimed to evaluate the impact of four cooling circuit materials on the growth of N. fowleri in a freshwater biofilm formed at 42°C and under a hydrodynamic shear rate of 17 s-1 (laminar flow): polyvinyl chloride, stainless steel, brass, and titanium. Colonization of the freshwater biofilms by N. fowleri was found to be effective on polyvinyl chloride, stainless steel, and titanium. For these three materials, the ratio of (bacterial prey)/(amoeba) was found to control the growth of N. fowleri. All materials taken together, a maximum specific growth rate of 0.18 ± 0.07 h-1 was associated with a generation time of ~4 h. In contrast, no significant colonization of N. fowleri was found on brass. Therefore, the contribution of copper is strongly suspected.

Characterizing the development of biofilm in polyethylene pipes in the non-chlorinated Danish drinking-water distribution system

In newly commissioned drinking-water polyethylene (PE) pipes, biofilm develops on the inner pipe surface. The microbial community composition from colonization to the establishment of mature biofilms is less known, including the effect on the distributed water quality. Biofilm development was followed through 1.5 years in PE-pipe side streams at two locations of a full-scale, non-chlorinated drinking-water distribution system (leaving a waterworks versus 5-6 km from a waterworks) along with inlet and outlet water quality. Mature biofilms were established after ∼8-9 months, dominated by Proteobacteria, Actinobacteria and Saccharibacteria (61-93% relative abundance), with a higher diversity (OTUs/Shannon Index/16S rRNA gene amplicon sequencing) in pipes in the far end of the distribution system. Comamonadaceae, and specifically Aquabacterium (>30% of reads), dominated young (∼1.5-month-old) biofilms. Young biofilms were linked to increased microbiological counts in drinking water (HPC/ATP/qPCR), while the establishment of mature biofilms led to a drop in HPC and benefited the water quality, highlighting the importance of optimizing commissioning procedures for rapidly achieving mature and stable biofilms.

Bacterial communities of planktonic bacteria and mature biofilm in service lines and premise plumbing of a Megacity: Composition, Diversity, and influencing factors

Although simulated studies have provided valuable knowledge regarding the communities of planktonic bacteria and biofilms, the lack of systematic field studies have hampered the understanding of microbiology in real-world service lines and premise plumbing. In this study, the bacterial communities of water and biofilm were explored, with a special focus on the lifetime development of biofilm communities and their key influencing factors. The 16S rRNA gene sequencing results showed that both the planktonic bacteria and biofilm were dominated by Proteobacteria. Among the 15,084 observed amplicon sequence variants (ASVs), the 33 core ASVs covered 72.8 %, while the 12 shared core ASVs accounted for 62.2 % of the total sequences. Remarkably, it was found that the species richness and diversity of biofilm communities correlated with pipe age. The relative abundance of ASV2 (f_Sphingomonadaceae) was lower for pipe ages 40-50 years (7.9 %) than for pipe ages 10-20 years (59.3 %), while the relative abundance of ASV10 (f_Hyphomonadaceae) was higher for pipe ages 40-50 years (19.5 %) than its presence at pipe ages 20-30 years (1.9 %). The community of the premise plumbing biofilm had significantly higher species richness and diversity than that of the service line, while the steel-plastics composite pipe interior lined with polyethylene (S-PE) harbored significantly more diverse biofilm than the galvanized steel pipes (S-Zn). Interestingly, S-PE was enriched with ASV27 (g_Mycobacterium), while S-Zn pipes were enriched with ASV13 (g_Pseudomonas). Moreover, the network analysis showed that five rare ASVs, not core ASVs, were keystone members in biofilm communities, indicating the importance of rare members in the function and stability of biofilm communities. This manuscript provides novel insights into real-world service lines and premise plumbing microbiology, regarding lifetime dynamics (pipe age 10-50 years), and the influences of pipe types (premise plumbing vs. service line) and pipe materials (S-Zn vs. S-PE).

Quantifying the Dynamics of Bacterial Biofilm Formation on the Surface of Soft Contact Lens Materials Using Digital Holographic Tomography to Advance Biofilm Research

The increase in bacterial resistance to antibiotics in recent years demands innovative strategies for the detection and combating of biofilms, which are notoriously resilient. Biofilms, particularly those on contact lenses, can lead to biofilm-related infections (e.g., conjunctivitis and keratitis), posing a significant risk to patients. Non-destructive and non-contact sensing techniques are essential in addressing this threat. Digital holographic tomography emerges as a promising solution. This allows for the 3D reconstruction of the refractive index distribution in biological samples, enabling label-free visualization and the quantitative analysis of biofilms. This tool provides insight into the dynamics of biofilm formation and maturation on the surface of transparent materials. Applying digital holographic tomography for biofilm examination has the potential to advance our ability to combat the antibiotic bacterial resistance crisis. A recent study focused on characterizing biofilm formation and maturation on six soft contact lens materials (three silicone hydrogels, three hydrogels), with a particular emphasis on Staphylococcus epidermis and Pseudomonas aeruginosa, both common culprits in ocular infections. The results revealed species- and time-dependent variations in the refractive indexes and volumes of biofilms, shedding light on cell dynamics, cell death, and contact lens material-related factors. The use of digital holographic tomography enables the quantitative analysis of biofilm dynamics, providing us with a better understanding and characterization of bacterial biofilms.

Establishment and inactivation of mono-species biofilm in a semipilot-scale water distribution system using nanocomposite of silver nanoparticles/montmorillonite loaded cationic chitosan

This study presents a novel approach in the synthesis and characterization of nanocomposites comprising cationic chitosan (CCS) blended with varying concentrations of silver nanoparticles/montmorillonite (AgNPs/MMT). AgNPs/MMT was synthesized using soluble starch as a reducing and stabilizing agent. Subsequently, nanocomposites, namely CCS/AgMMT-0, CCS/AgMMT-0.5, CCS/AgMMT-1.5, and CCS/AgMMT-2.5, were developed by blending 2.5 g of CCS with 0, 0.5, 1.5, and 2.5 g of AgNPs/MMT, respectively, and the corresponding nanocomposites were prepared using ball milling technique. Transmission electron microscopy (TEM) analysis revealed the formation of nanocomposites that exhibiting nearly spherical morphologies. Dynamic light scattering (DLS) measurements displayed average particle sizes of 1183 nm, 131 nm, 140 nm, and 188 nm for CCS/AgMMT-0, CCS/AgMMT-0.5, CCS/AgMMT-1.5, and CCS/AgMMT-2.5, respectively. The narrow polydispersity index (~0.5) indicated uniform particle size distributions across the nanocomposites, affirming monodispersity. Moreover, the zeta potential values exceeding 30 mV across all nanocomposites that confirmed their stability against agglomeration. Notably, CCS/AgMMT-2.5 nanocomposite exhibited potent antibacterial and antibiofilm properties against diverse pipeline materials. Findings showed that after 15 days of incubation, the highest populations of biofilm cells, Pseudomonas aeruginosa biofilm, developed over UPVC, MDPE, DCI, and SS, with corresponding HPCs of 4.79, 6.38, 8.81, and 7.24 CFU/cm2. The highest cell densities of Enterococcus faecalis biofilm in the identical situation were 4.19, 5.89, 8.12, and 6.9 CFU/cm2. The nanocomposite CCS/AgMMT-2.5 exhibited the largest measured zone of inhibition (ZOI) against both P. aeruginosa and E. faecalis, with measured ZOI values of 19 ± 0.65 and 17 ± 0.21 mm, respectively. Remarkably, the research indicates that the youngest biofilm exhibited the most notable rate of inactivation when exposed to a dose of 150 mg/L, in comparison to the mature biofilm. These such informative findings could offer valuable insights into the development of effective antibiofilm agents and materials applicable in diverse sectors such as water treatment facilities, medical devices, and industrial pipelines.

Microbial ecology of drinking water from source to tap

As drinking water travels from its source, through various treatment processes, hundreds to thousands of kilometres of distribution network pipes, to the taps in private homes and public buildings, it is exposed to numerous environmental changes, as well as other microbes living in both water and on surfaces. This review aims to identify the key locations and factors that are associated with changes in the drinking water microbiome throughout conventional urban drinking water systems from the source to the tap water. Over the past 15 years, improvements in cultivation-independent methods have enabled studies that allow us to answer such questions. As a result, we are beginning to move towards predicting the impacts of disturbances and interventions resulting ultimately in management of drinking water systems and microbial communities rather than mere observation. Many challenges still exist to achieve effective management, particularly within the premise plumbing environment, which exhibits diverse and inconsistent conditions that may lead to alterations in the microbiota, potentially presenting public health risks. Finally, we recommend the establishment of global collaborative projects on the drinking water microbiome that will enhance our current knowledge and lead to tools for operators and researchers alike to improve global access to high-quality drinking water.

Effect and influence mechanism of biofilm formation on the biological stability of reclaimed water

Microorganisms and sediments in reclaimed water adhere to the inner walls of pipes or water tanks, forming biofilms that support the continuous growth of microorganisms. These biofilms provide a protective barrier, shielding bacteria from disinfectants. This study investigated the impact of biofilms on bacterial growth and reproduction in reclaimed water and the factors limiting bacterial growth in reclaimed graywater (GMR) and reclaimed mixed wastewater (MWR). The results revealed that biofilm biomass gradually increased and reached a maximum value on Days 20-25, and the biomass of organisms continued to decrease after 40 days. Biofilms serve as a source of bacteria, continuously releasing them into reclaimed water systems. The presence of biofilms reduced the biological stability of the reclaimed water, leading to water quality deterioration. The concentration of assimilable organic carbon in the reclaimed water showed a positive correlation with the heterotrophic bacterial count and Escherichia coli levels in both the reclaimed water and biofilms. The threshold value of chlorine for inhibiting biofilms in reclaimed water was no <2 mg/L. High concentrations of free chlorine delayed the growth of biofilms but did not reduce the final biomass generated by the biofilms. Carbon was the limiting factor for the biological stability of reclaimed water, while nitrogen, phosphorus, and inorganic salts were not limiting factors. Thus, minimizing the concentration of organic matter in reclaimed water can reduce the nutrient sources available for biofilm formation. This study provides support for advancements in the wastewater reuse industry.

Seasonal variations of biofilm C, N and S cycling genes in a pilot-scale chlorinated drinking water distribution system

Biofilms in drinking water distribution systems (DWDS) host diverse microorganisms. However, the functional attributes of DWDS biofilms and their associations with seasonality remain unclear. This study aims to characterize variations in the microbial metabolic traits of DWDS biofilms collected during different seasons, using a pilot-scale DWDS in dark under plug-flow conditions during one-year operation period. Network analysis was used to predict the functional gene hosts. The overall functional attributes determined by shotgun metagenomics exhibited significant differences among seasons. Genes associated with aromatic metabolism, fatty acid biosynthesis and degradation, and capsular extracellular polymeric substance (EPS) were significantly upregulated in summer owing to the higher temperatures and chlorine in the influent of the DWDS. Moreover, the pathways associated with nitrogen, sulfur, glycolysis, and tricarboxylic acid (TCA) cycling, as well as carbon fixation were reconstructed and displayed according to the sampling season. Nitrogen reduction pathways [dissimilatory nitrate reduction to ammonium (DNRA) 73 %, assimilatory nitrate reduction to ammonium (ANRA) 21 %] were identified in DWDS biofilms, but nitrogen oxidation pathways were not. Sulfur cycling were involved in diverse pathways and genes. Glycolysis and TCA cycling offered electron donors and energy sources for nitrogen and sulfur reduction in biofilms. Carbon fixation was observed in DWDS biofilms, with the predominant pathway for fixing carbon dioxide being the reductive citrate cycle (38 %). Constructed functional gene networks composed of carbon, nitrogen, and sulfur cycling-related genes demonstrated synergistic effects (Positive proportion: 63.52-71.09 %). In addition, from spring to autumn, the network complexity decreased and network modularity increased. The assembly mechanism of carbon, nitrogen and sulfur cycling-related genes was driven by stochastic processes for all samples. These results highlight the diverse functional genes in DWDS biofilms, their synergetic interrelationships, and the seasonality effect on functional attributes.

Effects of water chemistry and flow on lead release from plastic pipes versus copper pipes, implications for plumbing decontamination

Despite being corrosion-resistant, plastic potable water pipes might accumulate heavy metals on their surface if they convey metal-contaminated tap water. This study examined the influence of water pH and flow conditions on lead (Pb) release from new and biofilm-laden potable water pipes to provide insights regarding decontamination. For this purpose, biofilms were grown onto new crosslinked polyethylene (PEX-A), high-density polyethylene (HDPE), and copper pipes for three months. Lead was then deposited onto the new and biofilm-laden pipes through 5 d exposure experiments under flow conditions. After that, lead release experiments were conducted by exposing the lead-accumulated pipes to lead-free synthetic tap water for 5 d, under both stagnant and water flow conditions. The metal accumulation study showed no significant difference in lead uptake by new pipes and their biofilm-laden counterparts under flow conditions. This could be attributed to the detachment of biofilms that have accumulated lead as water flows through the pipes. Water flow conditions significantly influenced the lead release from new and biofilm-laden water pipes. A lower water pH of 5.0 increased the release of lead from plastic pipes into the contact water, compared to pH 6.0 and 7.8. The greatest percentage of lead was released from biofilm-laden HDPE pipes (5.3%, 120 h) compared to biofilm-laden copper pipes (3.9%, 6 h) and PEX-A (3.7%, 120 h) and after exposure to lead-free synthetic tap water at pH 5.0, under stagnant conditions. On the other hand, under water flow conditions, the greatest lead release was found for new PEX-A pipes (4.4%, 120 h), new HDPE pipes (2.7%, 120 h), and biofilm-laden copper pipes (3.7%, 2 h).

Niche Differentiation of Biofilm Microorganisms in a Full-scale Municipal Drinking Water Distribution System in China and Their Implication for Biofilm Control

Biofilms on the inner surface of a drinking water distribution system (DWDS) affect water quality and stability. Understanding the niche differentiation of biofilm microbial communities is necessary for the efficient control of DWDS biofilms. However, biofilm studies are difficult to conduct in the actual DWDS because of inaccessibility to the pipes buried underground. Taking the opportunity of infrastructure construction and relevant pipeline replacement in China, biofilms in a DWDS (a water main and its branch pipes) were collected in situ, followed by analysis on the abundances and community structures of bacterial and archaeal using quantitative PCR and high-throughput sequencing, respectively. Results showed that archaea were detected only in the biofilms of the water main, with a range of 9.4×103~1.1×105 copies/cm2. By contrast, bacteria were detected in the biofilms of branch pipes and the distal part of the water main, with a range of 8.8×103~9.6×106 copies/cm2. Among the biofilm samples, the archaeal community in the central part of the water main showed the highest richness and diversity. Nitrosopumilus was found to be predominant (86.22%) in the biofilms of the proximal part of the water main. However, Methanobrevibacter (87.15%) predominated in the distal part of the water main. The bacterial community of the water main and branch pipes was primarily composed of Firmicutes and Proteobacteria at the phylum level, respectively. Regardless of archaea or bacteria, only few operational taxonomic units (OTUs) (<0.5% of total OTUs) were shared by all the biofilms, indicating the niche differentiation of biofilm microorganisms. Moreover, the high Mn content in the biofilms of the distal sampling location (D3) in the water main was linked to the predominance of Bacillus. Functional gene prediction revealed that the proportion of infectious disease-related genes was 0.44-0.67% in the tested biofilms. Furthermore, functional genes related to the resistance of the bacterial community to disinfections and antibiotics were detected in all the samples, that is, glutathione metabolism-relating genes (0.14-0.65%) and beta-lactam resistance gene (0.01-0.05%). The results of this study indicate the ubiquity of archaea and bacteria in the biofilms of water main and branch pipes, respectively, and pipe diameters could be a major influencing factor on bacterial community structure. In the water main, the key finding was the predominant existence of archaea, particularly Nitrosopumilus and methanogen. Hence, their routine monitoring and probable influences on water quality in pipelines with large diameter should be given more attention. Besides, since Mn-related Bacillus and suspected pathogenic Enterococcus were detected in the biofilm, supplementation of disinfectant may be a feasible strategy for inhibiting their growth and ensuring water quality. In addition, the monitoring on their abundance variation could help to determine the frequency and methods of pipeline maintenance.

Realism-based assessment of the efficacy of potassium peroxymonosulphate on Stenotrophomonas maltophilia biofilm control

The potential of pentapotassium bis(peroxymonosulphate) bis(sulphate) (OXONE) to control biofilms in drinking water distribution systems (DWDS) was evaluated and compared to chlorine disinfection. Mature biofilms of drinking water (DW)-isolated Stenotrophomonas maltophilia were formed using a simulated DWDS with a rotating cylinder reactor (RCR). After 30 min of exposure, OXONE at 10 × minimum bactericidal concentration (MBC) caused a significant 4 log reduction of biofilm culturability in comparison to the unexposed biofilms and a decrease in the number of non-damaged cells below the detection limit (4.8 log cells/cm2). The effects of free chlorine were restricted to approximately 1 log reduction in both biofilm culturability and non-damaged cells. OXONE in synthetic tap water (STW) at 25 ºC was more stable over 40 days than free chlorine in the same conditions. OXONE solution exhibited a disinfectant decrease of about 10% of the initial concentration during the first 9 days, and after this time the values remained stable. Whereas possible reaction of chlorine with inorganic and organic substances in STW contributed to free chlorine depletion of approximately 48% of the initial concentration. Electron paramagnetic resonance (EPR) spectroscopy studies confirmed the presence of singlet oxygen and other free radicals during S. maltophilia disinfection with OXONE. Overall, OXONE constitutes a relevant alternative to conventional DW disinfection for effective biofilm control in DWDS.

The Behavior of Polymeric Pipes in Drinking Water Distribution System-Comparison with Other Pipe Materials

The inner walls of the drinking water distribution system (DWDS) are expected to be clean to ensure a safe quality of drinking water. Complex physical, chemical, and biological processes take place when water comes into contact with the pipe surface. This paper describes the impact of leaching different compounds from the water supply pipes into drinking water and subsequent risks. Among these compounds, there are heavy metals. It is necessary to prevent these metals from getting into the DWDS. Those compounds are susceptible to impacting the quality of the water delivered to the population either by leaching dangerous chemicals into water or by enhancing the development of microorganism growth on the pipe surface. The corrosion process of different pipe materials, scale formation mechanisms, and the impact of bacteria formed in corrosion layers are discussed. Water treatment processes and the pipe materials also affect the water composition. Pipe materials act differently in the flowing and stagnation conditions. Moreover, they age differently (e.g., metal-based pipes are subjected to corrosion while polymer-based pipes have a decreased mechanical resistance) and are susceptible to enhanced bacterial film formation. Water distribution pipes are a dynamic environment, therefore, the models that are used must consider the changes that occur over time. Mathematical modeling of the leaching process is complex and includes the description of corrosion development over time, correlated with a model for the biofilm formation and the disinfectants-corrosion products and disinfectants-biofilm interactions. The models used for these processes range from simple longitudinal dispersion models to Monte Carlo simulations and 3D modeling. This review helps to clarify what are the possible sources of compounds responsible for drinking water quality degradation. Additionally, it gives guidance on the measures that are needed to maintain stable and safe drinking water quality.

The impact of potassium peroxymonosulphate and chlorinated cyanurates on biofilms of Stenotrophomonas maltophilia: effects on biofilm control, regrowth, and mechanical properties

The activity of two chlorinated isocyanurates (NaDCC and TCCA) and peroxymonosulphate (OXONE) was evaluated against biofilms of Stenotrophomonas maltophilia, an emerging pathogen isolated from drinking water (DW), and for the prevention of biofilm regrowth. After disinfection of pre-formed 48 h-old biofilms, the culturability was reduced up to 7 log, with OXONE, TCCA, and NaDCC showing more efficiency than free chlorine against biofilms formed on stainless steel. The regrowth of biofilms previously exposed to OXONE was reduced by 5 and 4 log CFU cm-2 in comparison to the unexposed biofilms and biofilms exposed to free chlorine, respectively. Rheometry analysis showed that biofilms presented properties of viscoelastic solid materials, regardless of the treatment. OXONE reduced the cohesiveness of the biofilm, given the significant decrease in the complex shear modulus (G*). AFM analysis revealed that biofilms had a fractured appearance and smaller bacterial aggregates dispersed throughout the surface after OXONE exposure than the control sample. In general, OXONE has been demonstrated to be a promising disinfectant to control DW biofilms, with a higher activity than chlorine. The results also show the impact of the biofilm mechanical properties on the efficacy of the disinfectants in biofilm control.

Stability of Drinking Water Distribution Systems and Control of Disinfection By-Products

The stability of drinking water distribution systems and the management of disinfection by-products are critical to ensuring public health safety. In this paper, the interrelationships between corrosion products in the network, microbes, and drinking water quality are elucidated. This review also discusses the mechanisms through which corrosive by-products from the piping network influence the decay of disinfectants and the formation of harmful disinfection by-products. Factors such as copper corrosion by-products, CuO, Cu₂O, and Cu²⁺ play a significant role in accelerating disinfectant decay and catalyzing the production of by-products. Biofilms on pipe walls react with residual chlorine, leading to the formation of disinfection by-products (DBPs) that also amplify health risks. Finally, this paper finally highlights the potential of peroxymonosulfate (PMS), an industrial oxidant, as a disinfectant that can reduce DBP formation, while acknowledging the risks associated with its corrosive nature. Overall, the impact of the corrosive by-products of pipe scale and microbial communities on water quality in pipe networks is discussed, and recommendations for removing DBPs are presented.

The bacterial biofilm resistome in drinking water distribution systems: A systematic review

Antibiotic resistance in drinking water systems poses human health risks. Earlier studies, including reviews on antibiotic resistance in drinking water systems are limited to the occurrence, behaviour and fate in bulk raw water and drinking water treatment systems. By comparison, reviews on the bacterial biofilm resistome in drinking water distribution systems are still limited. Therefore, the present systematic review investigates the occurrence, behaviour and fate and, detection methods of bacterial biofilm resistome in the drinking water distribution systems. A total of 12 original articles drawn from 10 countries were retrieved and analyzed. Antibiotic resistant bacteria and antibiotic resistance genes detected in biofilms include those for sulfonamides, tetracycline, and beta-lactamase. The genera detected in biofilms include Staphylococcus, Enterococcus, Pseudomonas, Ralstonia, Mycobacteria, as well as Enterobacteriaceae family and other gram-negative bacteria. The presence of Enterococcus faecium, Staphylococcusaureus, Klebsiella pneumoniae, Acinetobacterbaumannii, Pseudomonas aeruginosa, and Enterobacter species (ESKAPE bacteria) among the detected bacteria points to potential human exposure and health risks especially for susceptible individuals via the consumption of drinking water. Besides, the effects of water quality parameter and residual chlorine, the physico-chemical factors controlling the emergence, persistence and fate of the biofilm resistome are still poorly understood. Culture-based methods, and molecular methods, and their advantages and limitations are discussed. The limited data on the bacterial biofilm resistome in drinking water distribution system points to the need for further research. To this end, future research directions are discussed including understanding the formation, behaviour, and fate of the resistome and the controlling factors.

Seasonal variations of microbial community and antibiotic resistome in a suburb drinking water distribution system in a northern Chinese city

Antibiotic resistance genes (ARGs) are an emerging issue for drinking water safety. However, the seasonal variation of ARGs in drinking water distribution systems (DWDS) is still unclear. This work revealed the tempo-spatial changes of microbial community, ARGs, mobile genetic elements (MGEs) co-occurring with ARGs, ARG hosts in DWDS bulk water by means of metagenome assembly. The microbial community and antibiotic resistome varied with sampling season and site. Temperature, ammonia, chlorite and total plate count (TPC) drove the variations of microbial community structure. Moreover, environmental parameters (total organic carbon (TOC), chlorite, TPC and hardness) shifted antibiotic resistome. ARGs and MGEs co-occurring with ARGs showed higher relative abundance in summer and autumn, which might be attributed to detached pipe biofilm. In particular, ARG-bacitracin and plasmid were the predominant ARG and MGE, respectively. ARG hosts changed with season and site and were more diverse in summer and autumn. In winter and spring, Limnohabitans and Mycobacterium were the major ARG hosts as well as the dominant genera in microbial community. In addition, in summer and autumn, high relative abundance of Achromobacter and Stenotrophomonas were the hosts harboring many kinds of ARGs and MGEs at site in a residential zone (0.4 km from the water treatment plant). Compared with MGEs, microbial community had a greater contribution to the variation of antibiotic resistome. This work gives new insights into the dynamics of ARGs in full-scale DWDS and the underlying factors.

Early succession of biofilm bacterial communities in newly built drinking water pipelines via multi-area analysis

Biofilms inhabiting pipeline walls are critical to drinking water quality and safety. With massive pipeline replacement underway, however, biofilm formation process in newly built pipes and its effects on water quality are unclear. Moreover, differences and connections between biofilms in newly built and old pipes are unknown. In this study, early succession (≤ 120 days) of biofilm bacterial communities (abundance and diversity) in upper, middle and bottom areas of a newly built cement-lined ductile iron pipeline were evaluated using improved Propella™ biofilm reactor and multi-area analysis. A comparison with old pipelines (grey cast iron, 10 years) was performed. In the newly built pipeline, the abundance of biofilm bacteria did not change significantly between 40 and 80 days, but increased significantly between 80 and 120 days. The biofilm bacterial abundance (per unit area) in the bottom area was always higher than that in the upper and middle areas. Based on alpha diversity index and PCoA results, biofilm bacterial community richness, diversity and composition did not change significantly during the 120-day operation. Besides, biofilm shedding from the walls of newly built pipeline significantly increased bacterial abundance in the outlet water. Opportunistic pathogen-containing genera, such as Burkholderia, Acinetobacter and Legionella, were identified in both water and biofilm samples from newly built pipelines. The comparison between new and old pipelines suggested a higher bacterial abundance per unit area at the middle and bottom areas in old pipelines. Moreover, the bacterial community composition of biofilms in old pipelines was similar to that of newly built pipelines. These results contribute to accurate prediction and management of biofilm microbial communities in drinking water pipelines, ensuring the biosafety of drinking water. KEY POINTS: • Biofilm bacterial communities in different areas of pipe wall were revealed. • The abundance of biofilm bacteria increased significantly between 80 and 120 days. • Biofilm bacterial community compositions of newly built and old pipes were similar.

Legionella pneumophila Risk from Air–Water Cooling Units Regarding Pipe Material and Type of Water

Legionellosis is a respiratory disease related to environmental health. There have been manifold studies of pipe materials, risk installations and legionellosis without considering the type of transferred water. The objective of this study was to determine the potential development of the causative agent Legionella pneumophila regarding air–water cooling units, legislative compliance, pipe material and type of water. Forty-four hotel units in Andalusia (Spain) were analysed with respect to compliance with Spanish health legislation for the prevention of legionellosis. The chi-square test was used to explain the relationship between material–water and legislative compliance, and a biplot of the first two factors was generated. Multiple correspondence analysis (MCA) was performed on the type of equipment, legislative compliance, pipe material and type of water, and graphs of cases were constructed by adding confidence ellipses by categories of the variables. Pipe material–type of water (p value = 0.29; p < 0.05) and legislative compliance were not associated (p value = 0.15; p < 0.05). Iron, stainless steel, and recycled and well water contributed the most to the biplot. MCA showed a global pattern in which lead, iron and polyethylene were well represented. Confidence ellipses around categories indicated significant differences among categories. Compliance with Spanish health legislation regarding the prevention and control of legionellosis linked to pipe material and type of water was not observed.

Co-occurrence of phthalate esters and perfluoroalkyl substances affected bacterial community and pathogenic bacteria growth in rural drinking water distribution systems

The adverse health effects of phthalate esters (PAEs) and perfluoroalkyl substances (PFAS) in drinking water have attracted considerable attention. Our study investigated the effects of PAEs and PFAS on the bacterial community and the growth of potential human pathogenic bacteria in rural drinking water distribution systems. Our results showed that the total concentration of PAEs and PFAS ranged from 1.02 × 10² to 1.65 × 10⁴ ng/L, from 4.40 to 1.84 × 10² ng/L in rural drinking water of China, respectively. PAEs concentration gradually increased and PFAS slowly decreased along the pipeline distribution, compared to concentrations in the effluents of rural drinking water treatment plants. The co-occurrence of higher concentrations of PAEs and PFAS changed the structure and function of the bacterial communities found within these environments. The bacterial community enhanced their ability to respond to fluctuating environmental conditions through up-regulation of functional genes related to extracellular signaling and interaction, as well as genes related to replication and repair. Under these conditions, co-occurrence of PAEs and PFAS promoted the growth of potential human pathogenic bacteria (HPB), therefore increasing the risk of the development of associated diseases among exposed persons. The main HPB observed in this study included Burkholderia mallei, Mycobacterium tuberculosis, Klebsiella pneumoniae, Acinetobacter calcoaceticus, Escherichia coli, and Pseudomonas aeruginosa. Contaminants including particles, microorganisms, PAEs and PFAS were found to be released from corrosion scales and deposits of pipes and taps, resulting in the increase of the cytotoxicity and microbial risk of rural tap water. These results are important to efforts to improve the safety of rural drinking water.

Microplastics in urban waters and its effects on microbial communities: a critical review

Microplastic (MP) pollution is one of the emerging threats to the water and terrestrial environment, forcing a new environmental challenge due to the growing trend of plastic released into the environment. Synthetic and non-synthetic plastic components can be found in rivers, lakes/reservoirs, oceans, mountains, and even remote areas, such as the Arctic and Antarctic ice sheets. MPs' main challenge is identifying, measuring, and evaluating their impacts on environmental behaviors, such as carbon and nutrient cycles, water and wastewater microbiome, and the associated side effects. However, until now, no standardized methodical protocols have been proposed for comparing the results of studies in different environments, especially in urban water and wastewater. This review briefly discusses MPs' sources, fate, and transport in urban waters and explains methodological uncertainty. The effects of MPs on urban water microbiomes, including urban runoff, sewage wastewater, stagnant water in plumbing networks, etc., are also examined in depth. Furthermore, this study highlights the pathway of MPs and their transport vectors to different parts of ecosystems and human life, particularly through mediating microbial communities, antibiotic-resistant genes, and biogeochemical cycles. Overall, we have briefly highlighted the present research gaps, the lack of appropriate policy for evaluating microplastics and their interactions with urban water microbiomes, and possible future initiatives.

Challenges and perspectives of quantitative microbiome profiling in food fermentations

Spontaneously fermented foods are consumed and appreciated for thousands of years although they are usually produced with fluctuated productivity and quality, potentially threatening both food safety and food security. To guarantee consistent fermentation productivity and quality, it is essential to control the complex microbiota, the most crucial factor in food fermentations. The prerequisite for the control is to comprehensively understand the structure and function of the microbiota. How to quantify the actual microbiota is of paramount importance. Among various microbial quantitative methods evolved, quantitative microbiome profiling, namely to quantify all microbial taxa by absolute abundance, is the best method to understand the complex microbiota, although it is still at its pioneering stage for food fermentations. Here, we provide an overview of microbial quantitative methods, including the development from conventional methods to the advanced quantitative microbiome profiling, and the application examples of these methods. Moreover, we address potential challenges and perspectives of quantitative microbiome profiling methods, as well as future research needs for the ultimate goal of rational and optimal control of microbiota in spontaneous food fermentations. Our review can serve as reference for the traditional food fermentation sector for stable fermentation productivity, quality and safety.

Stagnation trigger changes to tap water quality in winter season: Novel insights into bacterial community activity and composition

The drinking water distribution system is important for water supply and it affects the quality of the drinking water. Indoor pipeline water quality is regulated by physical, hydraulic and biological elements, such as indoor temperature and stagnation. In this work, the effects of indoor heating and overnight stagnation on the variation in bacterial community structure and the total cell count were assessed by full-length 16S rRNA gene sequencing and flow cytometry, respectively. The results exhibited that the average intact cell count was 6.99 × 10⁴ cells/mL and the low nucleic acid (LNA) bacteria was 4.48 × 10⁴ cells/mL after stagnation. The average concentration of total and intracellular adenosine triphosphate (ATP) was 3.64 × 10^-12 gATP/mL and 3.13 × 10^-17 gATP/cell in stagnant water, respectively. The growth of LNA cells played a crucial role in increasing ATP. The dominant phylum observed was Proteobacteria (87.21 %), followed by Actinobacteria (8.25 %). Opportunistic pathogens increased the risk of disease in stagnant water (up to 1.2-fold for Pseudomonas sp. and 5.8-fold for Mycobacterium sp.). Meanwhile, structural equation model (SEM) and redundancy analysis (RDA) also illustrated that water temperature, residual chlorine and Fe significantly affected the abundance and composition of bacterial community. Taking together, these results show response of tap water quality to overnight stagnation and indoor heating, and provide scientific basis for drinking water security management in winter season.

Bacterial community structure and metabolic activity of drinking water pipelines in buildings: A new perspective on dual effects of hydrodynamic stagnation and algal organic matter invasion

Eutrophication and algal blooms have become global issues. The drinking water treatment process suffers from pollution by algal organic matter (AOM) through cell lysis during the algal blooms. Nevertheless, it remains unclear how AOM invasion affects water quality and microbial communities in drinking water, particularly in the stagnant settings. In this study, the addition of AOM caused the residual chlorine to rapidly degrade and below the limit of 0.05 mg/L, while the NO₂^--N concentration ranged from 0.11 to 3.71 mg/L. Additionally, total bacterial counts increased and subsequently decreased. The results of Biolog demonstrated that the AOM significantly improved the utilization capacity of carbon sources and changed the preference for carbon sources. Full-length 16S rRNA gene sequencing and network modeling revealed a considerable reduction in the abundance of Proteobacteria, whereas that of Bacteroidetes increased significantly under the influence of AOM. Furthermore, the species abundance distributions of the Microcystis group and Scenedesmus group was most consistent with the Mandelbrot model. According to redundancy analysis and structural equation modeling, the bacterial community structure of the control group was most positively regulated by the free residual chlorine concentrations, whereas the Microcystis group and Scenedesmus group were positively correlated with the total organic carbon (TOC) concentration. Overall, these findings provide a scientific foundation for the evolution of drinking water quality under algae bloom pollution.

Mechanism of Biofilm Formation on Installation Materials and Its Impact on the Quality of Tap Water

In the conducted study, an attempt was made to verify and evaluate the impact of the biofilm formed on the surfaces of the installation material on the quality and sanitary safety of tap water reaching the consumer. For biofilm studies, fractal analysis and quantitative bacteriological analysis were used. The quality of tap water flowing through the experimental installation (semi-technical scale) was determined using physicochemical and microbiological parameters. The quantitative analysis of the biofilm showed that an increase in the number of microorganisms was observed in the initial phase of biofilm formation (reached 1.4 × 104 CFU/mL/cm2 on day 14). During this period, there was a chaotic build-up of bacterial cells, as evidenced by an increase in the roughness of the profile lines. Unstable elevations of the biofilm formed in this way could be easily detached from the structure of the material, which resulted in deterioration of the bacteriological quality of the water leaving the installation. The obtained results indicate that the biofilm completely and permanently covered the surface of the tested material after 25 days of testing (the surface roughness described by the fractal dimension decreased). Moreover, the favorable temperature (22.6 °C) and the recorded decrease in the content of inorganic nitrogen (by 15%), phosphorus (by 14%), and dissolved oxygen (by 15%) confirm the activity of microorganisms. The favorable environmental conditions in the installation (the presence of nutrients, low chlorine concentration, and high temperature) contributed to the secondary development of microorganisms, including pathogenic organisms in the tested waters.

Fate of microplastics in the drinking water production

Microplastics are ubiquitous and consequently enter drinking water treatment plants. Knowledge of the microplastic fate in drinking water production is still very limited, although explorative studies have shown tap water contains low contents of microplastics. In this study, we measure microplastic concentrations in drinking water sources and assess the effectiveness of various drinking water treatment facilities to reduce the microplastic concentrations in water to gain insight into the fate of microplastics. Two analytical techniques, laser direct infrared spectroscopy (LDIR) and optical microscopy, have been applied to cover the particle size range from 20 µm to 5 mm. In total five different drinking water sites were investigated using four different types of raw water (groundwater, surface water, dune filtrate and riverbank filtrate) for drinking water production. This research shows that drinking water treatment removes the majority of microplastics and that concentration of microplastics larger than 20 µm in tap water is less than 2 microplastics particles per litre. Between the different raw water sources it is found that groundwater had by far the lowest microplastics concentrations (< 1.000 microplastics per m³) and the highest concentration was found in riverine water, up to 460.000 particles per m³, specifically in the Lek Canal () (a canal connected to the river Rhine). On average the most abundant plastics found are polyamide (PA, 33%), polyethylene terephthalate (PET, 15%), rubbers (10%), polyethylene (PE, 10%) and chlorinated polyethylene (CPE, 7%). This study also showed that natural treatment steps, such as dune infiltration and sedimentation, remove microplastics effectively. However, this may introduce an adverse effect where microplastics potentially accumulate in the sediment and environment.

Water and biofilm in drinking water distribution systems in the Netherlands

To keep the high quality of drinking water in the future for non-chlorinated drinking water systems, knowledge about the variables that most strongly affect this quality is necessary in order to know where to focus on and possibly even change aspects of drinking water production and distribution. Therefore, the aim of this study was to investigate which variables (source of drinking water, growth potential and pipe material type) have the biggest influence on bacterial community composition and biomass concentration of drinking water and biofilm in distribution systems. Ten different distribution systems were sampled for water and biofilm, obtained from four different pipe materials, throughout the Netherlands. The distribution systems are supplied either with drinking water produced from groundwater or surface water, and differ in drinking water quality parameters such as the growth potential. We found a significant relationship for growth potential and ATP concentration in water, but for the ATP in the biofilm none of the parameters showed a significant effect. Furthermore, the source of the drinking water and the pipe material did not significantly affect the ATP concentration in water and biofilm. The bacterial composition of in both water and biofilm was significantly different between distribution systems delivering water with low and high growth potential and between drinking water produced from groundwater or surface water. In contrast, the different pipe materials did not significantly affect composition of biofilm-associated communities. We conclude from these results that the growth potential of the treated water best explains the variation in biomass and bacterial composition in water and biofilm of non-chlorinated drinking water distribution systems followed by the drinking water source, whereas pipe materials seem to be of lesser importance.

Impact of pipe material and chlorination on the biofilm structure and microbial communities

Pipe material and residual chlorine are key factors for the drinking water distribution system, and understanding the biofilm ecosystem is vital for water quality safeguard. The aim of our study was to determine the influence of pipe materials (ductile iron, steel, polyethylene) and chlorination on the biofilm structure and microbial community, as shown by the physicochemical properties, extracellular polymeric substances (EPS) structural characteristics, bacterial community composition, and functional traits. EPS spatial properties were studied based on a semi-quantitative confocal laser scanning microscope (CLSM) description. Regarding the impact of chlorination, residule chlorine (1.0 ± 0.3 mg L^-1 free chlorine) could inhibit the bacteria colonization, and initiate a potential response to external disinfectants revealed by the EPS spatial distribution changes and communities variation compared to unchlorinated system. Regarding the impact of pipe material, polyethylene (PE) biofilms displayed lower biomass, loose zoogloea structure, lower proteins and polysaccharides content, and poor microbial diversity in contrast to ductile iron and steel biofilms. Pipe material was the more possible driving factor of the biofilm community composition compared to the chlorination based on principal coordinates analysis (PCoA) and permutational multivariate analysis of variance (PERMANOVA). Actinobacteria was dominant in the PE biofilms (45.57%-83.32%), while Alphaproteobacteria (34.30%-73.22%) and Gammaproteobacteria (6.46%-36.82%) were the major classes in the steel and ductile iron biofilms. The genus Rhodococcus was predominant in the PE biofilms. Rhodococcus, Pseudomonas, and Sphingomonas seemed to have a better growth advantage in the chlorinated system and display a stronger disinfectant resistance. Functional sketch prediction indicated the potential impact of pipe material and chlorination on functional pathway abundnce, possible functional pathways associated with infectious disease included. This study provides insights into the impact of pipe material and chlorination on biofilm structure and microbial community and might help to develop monitoring or maintenance strategies to protect the biosafety of the drinking water.

Effect of Particle Concentration and Pipe Materials on the Formation of Biofilms in Drinking Water Distribution Systems

Microorganism rebreeding and biofilm shedding enter the water body in the process of a drinking water distribution system (DWDS), which poses a threat to public health. Particles in water can gather pollutants as well as providing favorable growth conditions for bacteria. To date, there are a few studies which focus on the relationship between particles and biofilm formation. Therefore, the microbial diversity of biofilms in the different pipe materials and the effect on particle concentration on biofilm formation were investigated in this study. Experiments were carried out under a simulative DWDS (including iron (DI) and polyvinyl chloride (PVC) pipe). The results showed that the microbial diversity in biofilms followed this order: DI pipe > PVC pipe > DI pipe (upper). Moreover, the microbial biomass of biofilm and the fluorescence intensity of extracellular polymeric substances (EPS, produced by microorganisms) were the largest in the absence of particles. The amount of biofilm bacterial and the fluorescence intensity of EPS both showed first an increasing and then decreasing trend with particle concentration increasing. When particle concentration was relatively low, the absorption of particles and bacteria played a major role, however, with the increasing particle concentration, more stable particle–particle were formed and thus, EPS was easily extracted, resulting in the increase of fluorescence intensity of EPS.