Inkinen J, Jayaprakash B, Ahonen M, Pitkänen T, Mäkinen R, Pursiainen A, Santo Domingo JW, Salonen H, Elk M, Keinänen-Toivola MM. Bacterial community changes in copper and PEX drinking water pipeline biofilms under extra disinfection and magnetic water treatment. Journal of applied microbiology. 2017 Dec 9. doi: 10.1111/jam.13662.
AIMS: To study stability of biofilms and water quality in pilot scale drinking water copper and PEX pipes in changing conditions (extra disinfection, magnetic water treatment MWT).
METHODS AND RESULTS: Next-generation sequencing (NGS) of 16S ribosomal RNA genes (rDNA) to describe total bacterial community and ribosomal RNA (rRNA) to describe active bacterial members in addition to traditional microbiological methods were applied. Biofilms from control copper and PEX pipes shared same most abundant bacteria (Methylobacterium spp., Sphingomonas spp., Zymomonas spp.) and average species diversities (Shannon 3.8-4.2) in rDNA and rRNA libraries whereas few of the taxa differed by their abundance such as lower total Mycobacterium spp. occurrence in copper (<0.02%) to PEX (<0.2%) pipes. Extra disinfection (total chlorine increase from ca. 0.5 to 1 mg l-1 ) affected total and active population in biofilms seen as decrease of many bacterial species and diversity (Shannon 2.7, P < 0.01, rRNA) and increase of Sphingomonas spp. as compared to control samples. Further, extra disinfected copper and PEX samples formed separate clusters in unweighted non-metric multidimensional scaling plot (rRNA) similarly to MWT-treated biofilms of copper (but not PEX) pipes that instead showed higher species diversity (Shannon 4.8, P < 0.05 interaction).
CONCLUSIONS: Minor chlorine dose addition increased selection pressure and many species were sensitive to chlorination. Pipe material seemed to affect mycobacteria occurrence, and bacterial communities with MWT in copper but not in PEX pipes.
SIGNIFICANCE AND IMPACT OF THE STUDY: This study using rRNA showed that chlorination affects especially active fraction of bacterial communities. Copper and PEX differed by the occurrence of some bacterial members despite similar community profiles.
Miller HC, Morgan MJ, Wylie JT, Kaksonen AH, Sutton D, Braun K, Puzon GJ. Elimination of Naegleria fowleri from bulk water and biofilm in an operational drinking water distribution system. Water research. 2016 Nov 27;110:15-26. doi: 10.1016/j.watres.2016.11.061.
Global incidence of primary amoebic meningoencephalitis cases associated with domestic drinking water is increasing. The need for understanding disinfectant regimes capable of eliminating the causative microorganism, Naegleria fowleri, from bulk water and pipe wall biofilms is critical. This field study demonstrated the successful elimination of N. fowleri from the bulk water and pipe wall biofilm of a persistently colonised operational drinking water distribution system (DWDS), and the prevention of further re-colonisation. A new chlorination unit was installed along the pipe line to boost the free chlorine residual to combat the persistence of N. fowleri. Biofilm and bulk water were monitored prior to and after re-chlorination (RCl), pre-rechlorination (pre-RCl) and post-rechlorination (post-RCl), respectively, for one year. A constant free chlorine concentration of > 1 mg/L resulted in the elimination of N. fowleri from both the bulk water and biofilm at the post-RCl site. Other amoeba species were detected during the first two months of chlorination, but all amoebae were eliminated from both the bulk water and biofilm at post-RCl after 60 days of chlorination with free chlorine concentrations > 1 mg/L. In addition, a dynamic change in the biofilm community composition and a four log reduction in biofilm cell density occurred post-RCl. The pre-RCl site continued to be seasonally colonised by N. fowleri, but the constant free chlorine residual of > 1 mg/L prevented N. fowleri from recolonising the bulk and pipe wall biofilm at the post-RCl site. To our knowledge, this is the first study to demonstrate successful removal of N. fowleri from both the bulk and pipe wall biofilm and prevention of re-colonisation of N. fowleri in an operational DWDS. The findings of this study are of importance to water utilities in addressing the presence of N. fowleri and other amoeba in susceptible DWDSs.
Mathieu L, Francius G, El Zein R, Angel E, Block JC. Bacterial repopulation of drinking water pipe walls after chlorination. Biofouling. Biofouling. 2016 Sep;32(8):925-34. doi: 10.1080/08927014.2016.1212989/
The short-term kinetics of bacterial repopulation were evaluated after chlorination of high-density polyethylene (HDPE) colonized with drinking water biofilms and compared with bare HDPE surfaces. The effect of chlorination was partial as a residual biofilm persisted and was time-limited as repopulation occurred immediately after water resupply. The total number of bacteria reached the same levels on both the bare and chlorinated biofilm-fouled HDPE after a seven-day exposure to drinking water. Due to the presence of a residual biofilm, the hydrophobicity of chlorinated biofilm-fouled surface exhibited much lower adhesion forces (2.1 nN) compared to bare surfaces (8.9 nN). This could explain the rapid repopulation after chlorination, with a twofold faster bacterial accumulation rate on the bare HDPE surface. γ-Proteobacteria dominated the early stages of repopulation of both surfaces and a shift in the dominance occurred over the colonization time. Such observations define a timescale for cleaning frequency in industrial environments and guidelines for a rinsing procedure using drinking water.
Liu S, Gunawan C, Barraud N, Rice SA, Harry EJ, Amal R. Understanding, Monitoring and Controlling Biofilm Growth in Drinking Water Distribution Systems. Environ Sci Techno. 2016 Aug 1.
In drinking water distribution systems (DWDS), biofilms are the predominant mode of microbial growth with the presence of extracellular polymeric substance (EPS) protecting the biomass from environmental and shear stresses. Biofilm formation poses a significant problem to the drinking water industry as a potential source of bacterial contamination, including pathogens and in many cases also affecting the taste and odor of drinking water and promotes corrosion of pipes. This article critically reviews important research findings on biofilm growth in DWDS, examining the factors affecting their formation and characteristics, as well as the various technologies to characterize, monitor and ultimately, to control their growth. Research indicates that temperature fluctuations potentially affect not only the initial bacteria-to-surface attachment but also the growth rates of biofilms. For the latter, the effect is unique for each type of biofilm-forming bacteria – ammonia oxidizing bacteria for example, grow more developed biofilms at typical summer temperature of 22○C compared to 12○C in fall , while the opposite occurs for the pathogenic V. cholera. Recent investigations have found formation of thinner yet denser biofilms under high and turbulent flow regimes of drinking water, in comparison to the more porous and loosely attached biofilms at low flow rates. Further, in addition to the rather well-known tendency of significant biofilm growth on corrosion-prone metal pipes, research efforts also found leaching of growth-promoting organic compounds from the increasingly popular use of polymer-based pipes. Knowledge of the unique microbial members of drinking water biofilms and importantly, the influence of water characteristics and operational conditions on their growth, can be applied to optimize various operational parameters to minimize biofilm accumulation. More detailed characterizations of the biofilm population size and structure are now feasible with fluorescence microscopy (epifluorescence and CLSM imaging with DNA, RNA, EPS, protein and lipid stains) and electron microscopy imaging (ESEM). Importantly, thorough identification of microbial fingerprints in drinking water biofilms is achievable with DNA sequencing techniques (the 16S rRNA gene-based identification), which have revealed prevalence of previously undetected bacterial members. Technologies are now moving toward in situ monitoring of biomass growth in distribution networks, including the development of optical fibres capable of differentiating biomass from chemical deposits. Taken together, management of biofilm growth in water distribution systems requires an integrated approach, starting from treatment of water prior to entering the networks, to potential implementation of ‘biofilm-limiting’ operational conditions and finally, to the careful selection of available technologies for biofilm monitoring and control. For the latter, conventional practices, including chlorine – chloramine disinfection, flushing of DWDS as well as nutrient removal, and emerging technologies are discussed with their associated challenges.
Stanish LF, Hull NM, Robertson CE, Harris JK, Stevens MJ, Spear JR, et al. (2016) Factors Influencing Bacterial Diversity and Community Composition in Municipal Drinking Waters in the Ohio River Basin, USA. PLoS ONE 11(6): e0157966. doi:10.1371/journal.pone.0157966
The composition and metabolic activities of microbes in drinking water distribution systems can affect water quality and distribution system integrity. In order to understand regional variations in drinking water microbiology in the upper Ohio River watershed, the chemical and microbiological constituents of 17 municipal distribution systems were assessed. While sporadic variations were observed, the microbial diversity was generally dominated by fewer than 10 taxa, and was driven by the amount of disinfectant residual in the water. Overall, Mycobacterium spp. (Actinobacteria), MLE1-12 (phylum Cyanobacteria), Methylobacterium spp., and sphingomonads were the dominant taxa. Shifts in community composition from Alphaproteobacteria and Betaproteobacteria to Firmicutes and Gammaproteobacteria were associated with higher residual chlorine. Alpha- and beta-diversity were higher in systems with higher chlorine loads, which may reflect changes in the ecological processes structuring the communities under different levels of oxidative stress. These results expand the assessment of microbial diversity in municipal distribution systems and demonstrate the value of considering ecological theory to understand the processes controlling microbial makeup. Such understanding may inform the management of municipal drinking water resources.
Revetta RP, Gomez-Alvarez V, Gerke TL, Santo Domingo JW, Ashbolt NJ. Changes in bacterial composition of biofilm in a metropolitan drinking water distribution system. Journal of Applied Microbiology. 2016 Mar 31. doi: 10.1111/jam.13150.
AIMS: This study examined the development of bacterial biofilms within a metropolitan distribution system. The distribution system is fed with different source water (i.e., groundwater, GW and surface water, SW) and undergoes different treatment processes in separate facilities.
METHODS AND RESULTS: The biofilm community was characterized using 16S rRNA gene clone libraries and functional potential analysis, generated from total DNA extracted from coupons in biofilm annular reactors fed with onsite drinking water for up to eighteen months. Differences in the bacterial community structure were observed between GW and SW. Representatives that explained the dissimilarity were associated with the classes Betaproteobacteria, Alphaproteobacteria, Actinobacteria, Gammaproteobacteria and Firmicutes. After nine months the biofilm bacterial community from both GW and SW were dominated by Mycobacterium species. The distribution of the dominant operational taxonomic unit (OTU) (Mycobacterium) positively correlated with the drinking water distribution system (DWDS) temperature.
CONCLUSIONS: In the current study, the biofilm community structure observed between GW and SW were dissimilar, while communities from different locations receiving SW did not show significant differences. The results suggest that source water and/or the water quality shaped by their respective treatment processes may play an important role in shaping the bacterial communities in the distribution system. In addition, several bacterial groups were present in all samples, suggesting that they are an integral part of the core microbiota of this DWDS.
SIGNIFICANCE AND IMPACT OF THE STUDY: These results provide an ecological insight into biofilm bacterial structure in chlorine-treated drinking water influenced by different water sources and their respective treatment processes.
Mi Z, Dai Y, Xie S, Chen C, Zhang X. Impact of disinfection on drinking water biofilm bacterial community. Journal of environmental sciences (China). 2015 Nov 1;37:200-5. doi: 10.1016/j.jes.2015.04.008.
Disinfectants are commonly applied to control the growth of microorganisms in drinking water distribution systems. However, the effect of disinfection on drinking water microbial community remains poorly understood. The present study investigated the impacts of different disinfectants (chlorine and chloramine) and dosages on biofilm bacterial community in bench-scale pipe section reactors. Illumina MiSeq sequencing illustrated that disinfection strategy could affect both bacterial diversity and community structure of drinking water biofilm. Proteobacteria tended to predominate in chloraminated drinking water biofilms, while Firmicutes in chlorinated and unchlorinated biofilms. The major proteobacterial groups were influenced by both disinfectant type and dosage. In addition, chloramination had a more profound impact on bacterial community than chlorination.