Occurrence and Fate of Ultramicrobacteria in a Full-Scale Drinking Water Treatment Plant

Abstract

Ultramicrobacteria (UMB) are omnipresent and numerically dominate in freshwater, as microbes can present in drinking water systems, however, the UMB communities that occur and their removal behaviors remain poorly characterized in drinking water treatment plants (DWTPs). To gain insights into these issues, we profiled bacterial cell density, community structure and functions of UMB and their counterpart large bacteria (LB) using flow cytometry and filtration paired with 16S rRNA gene high-throughput sequencing in a full-scale DWTP. Contrary to the reduction of bacterial density and diversity, the proportion of UMB in the total bacteria community increased as the drinking water treatment process progressed, and biological activated carbon facilitated bacterial growth. Moreover, UMB were less diverse than LB, and their community structure and predicted functions were significantly different. In the DWTP, UMB indicator taxa were mainly affiliated with α/β/γ-Proteobacteria, Deinococcus–Thermus, Firmicutes, Acidobacteria, and Dependentiae. In particular, the exclusive clustering of UMB at the phylum level, e.g., Parcubacteria, Elusimicrobia, and Saccharibacteria, confirmed the fact that the ultra-small size of UMB is a naturally and evolutionarily conserved trait. Additionally, the streamlined genome could be connected to UMB, such as candidate phyla radiation (CPR) bacteria, following a symbiotic or parasitic lifestyle, which then leads to the observed high connectedness, i.e., non-random intra-taxa co-occurrence patterns within UMB. Functional prediction analysis revealed that environmental information processing and DNA replication and repair likely contribute to the higher resistance of UMB to drinking water treatment processes in comparison to LB. Overall, the study provides valuable insights into the occurrence and fate of UMB regarding community structure, phylogenetic characteristics and potential functions in a full-scale DWTP, and it is a useful reference for beneficial manipulation of the drinking water microbiome.

Impact of UV irradiation at full scale on bacterial communities in drinking water

“…4), possibly due to the ability of these bacteria to repair UV damage and/or by surviving the UV exposure, and then regrowing faster than the other surviving taxa. As Pelagibacteraceae, or the SAR11 clade, are abundant in drinking water 47 and marine water 48,49 ; they may have acquired UV resistance to survive the UV exposure from the sun in their preferred niche and, with a large surface-to-volume ratio, efficient nutrient uptake in oligotrophic environments 50 allows them to grow faster than other members of the bacterial community 51 .…”

Microbiomes in drinking water treatment and distribution: a meta-analysis from source to tap

“…Some individual studies have focused on the relative importance of treatment in influencing downstream microbial communities, with the processes of filtration and chlorination reducing overall microbial diversity and affecting the abundance of particular phyla [39][40][41][42][43] . Biofilters can be extremely microbially diverse with different operational conditions causing changes to relative taxa abundances 39,43,46 . The upstream process also significantly affects filter biomass 16,17 .…”

Assessing bacterial infiltration through reverse osmosis membrane

“…However, size estimation for nonculturable bacteria is a major challenge; thus, the size of many bacterial species is not well known. Bacteria smaller than 0.1 µm 3 in volume are classified as ultramicrobacteria (Liu et al, 2018;Silbaq, 2009). Moreover, bacteria size can vary greatly depending on the environment and growing conditions (Colwell and Grimes, 2000).…”