Pyrosequencing Reveals Bacterial Communities in Unchlorinated Drinking Water Distribution System: An Integral Study of Bulk Water, Suspended Solids, Loose Deposits, and Pipe Wall Biofilm

Abstract

The current understanding of drinking water distribution system (DWDS) microbiology is limited to pipe wall biofilm and bulk water; the contributions of particle-associated bacteria (from suspended solids and loose deposits) have long been neglected. Analyzing the composition and correlation of bacterial communities from different phases helped us to locate where most of the bacteria are and understand the interactions among these phases. In the present study, the bacteria from four critical phases of an unchlorinated DWDS, including bulk water, pipe wall biofilm, suspended solids, and loose deposits, were quantified and identified by adenosine triphosphate analysis and pyrosequencing, respectively. The results showed that the bulk water bacteria (including the contribution of suspended solids) contributed less than 2% of the total bacteria. The bacteria associated with loose deposits and pipe wall biofilm that accumulated in the DWDS accounted for over 98% of the total bacteria, and the contributions of bacteria in loose deposits and pipe wall biofilm were comparable. Depending on the amount of loose deposits, its contribution can be 7-fold higher than the pipe wall biofilm. Pyrosequencing revealed relatively stable bacterial communities in bulk water, pipe wall biofilm, and suspended solids throughout the distribution system; however, the communities present in loose deposits were dependent on the amount of loose deposits locally. Bacteria within the phases of suspended solids, loose deposits, and pipe wall biofilm were similar in phylogenetic composition. The bulk water bacteria (dominated by Polaromonas spp.) were clearly different from the bacteria from the other three phases (dominated by Sphingomonas spp.). This study highlighted that the integral DWDS ecology should include contributions from all of the four phases, especially the bacteria harbored by loose deposits. The accumulation of loose deposits and the aging process create variable microenvironments inside loose deposits structures for bacteria to grow. Moreover, loose deposits protect the associated bacteria from disinfectants, and due to their mobility, the associated bacteria reach taps easily.

Impact of disinfection on drinking water biofilm bacterial community

“…Firmicutes has usually been found to be a minor component of DWDS bacterial communities in both in bulk waters (Kormas et al, 2010;Lu et al, 2013;Pinto et al, 2012;Vaz-Moreira et al, 2013), and biofilms (Lin et al, 2013;Liu et al, 2014;Revetta et al, 2013). Our previous study showed that Firmicutes was usually a rare species in pipe biofilms from a real urban DWDS, while in few cases it could be a major component of biofilm bacterial community (Wu et al, 2015).…”

“…To date, the relative importance of different proteobacterial classes in DWDS biofilm bacterial community remained unresolved (Wu et al, 2015). Previous studies showed the dominance of either Alphaproteobacteria (Douterelo et al, 2013;Gomez-Alvarez et al, 2014;Krishna et al, 2013), or Betaproteobacteria (Lee et al, 2005;Liu et al, 2014;Sun et al, 2014), while both of them could be dominant Wu et al, 2015). Moreover, Gammaproteobacteria could also be the largest bacterial group in DWDS biofilms (Douterelo et al, 2013;Wu et al, 2015).…”

“…Microbial growth in drinking water distribution systems (DWDS) can lead to a number of adverse problems, including proliferation of opportunistic pathogenic microorganisms (Berry et al, 2006;Emtiazi et al, 2004;Liu et al, 2013Liu et al, , 2014Lu et al, 2014). Disinfectants are commonly applied to lower the numbers of microorganisms in DWDS, maintaining a disinfectant residual.…”

“…In contrast, high-throughput sequencing, as a next generation sequencing technology, can provide a new opportunity to systematically compare the effects of physiochemical parameters on DWDS microbial communities Wu et al, 2015). To date, pyrosequencing analysis has found many applications in characterizing DWDS microbial community (Liu et al, 2012(Liu et al, , 2014Sun et al, 2014;Wang et al, 2014;Wu et al, 2015), however, Illumina MiSeq sequencing, the more recently developed high-throughput sequencing technology, has gained increasing popularity due to its lower costs and greater throughput, compared to pyrosequencing (Caporaso et al, 2012). So far, information on Illumina MiSeq sequencing of drinking water microbial community is still very limited (Wu et al, 2015).…”

A survey of indicator parameters to monitor regrowth in unchlorinated drinking water

“…The parameters that have been investigated in our study have been identified in all these three niches, but seem to differ in the preferred niche they occupy, with fungi being dominantly present in pipe wall biofilms, Aeromonas and HPCs in sediments and Mycobacterium spp., ATP and cell numbers in pipe wall biofilms and sediments. 15,24 Microbial growth in pipe wall biofilms, sediments and water will result in increased microbial numbers in drinking water and, therefore, regrowth indicators measured in drinking water should reflect growth in each of these three niches. In the past, ATP and cell counts have been proposed as alternative parameters for HPCs to determine microbial regrowth in drinking water distribution system.…”