title: Exploring the under-investigated "microbial dark matter" of drinking water treatment plants.
abstract: Scientists recently reported the unexpected detection of unknown or poorly studied bacterial diversity in groundwater. The ability to uncover this neglected biodiversity mainly derives from technical improvements, and the term "microbial dark matter" was used to group taxa poorly investigated and not necessarily monophyletic. We focused on such under-investigated microbial dark matter of drinking water treatment plant from groundwater, across carbon filters, to post-chlorination. We tackled this topic using an integrated approach where the efficacy of stringent water filtration (10000 MWCO) in recovering even the smallest environmental microorganisms was coupled with high-throughput DNA sequencing to depict an informative spectrum of the neglected microbial diversity. Our results revealed that the composition of bacterial communities varies across the plant system: Parcubacteria (OD1) superphylum is found mainly in treated water, while groundwater has the highest heterogeneity, encompassing non-OD1 candidate phyla (Microgenomates, Saccharibacteria, Dependentiae, OP3, OP1, BRC1, WS3). Carbon filters probably act as substrate for microorganism growth and contribute to seeding water downstream, since chlorination does not modify the incoming bacterial community. New questions arise about the role of microbial dark matter in drinking water. Indeed, our results suggest that these bacteria might play a central role in the microbial dynamics of drinking water.
authors.affiliation: University of Milan-Bicocca, ZooPlantLab, Biotechnology and Biosciences Department, Piazza della Scienza 2, 20126, Milan, Italy.
authors.forename: Antonia
authors.initials: A
authors.lastname: Bruno
authors.affiliation: University of Milan-Bicocca, ZooPlantLab, Biotechnology and Biosciences Department, Piazza della Scienza 2, 20126, Milan, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Sandionigi
authors.affiliation: National Research Council (CNR), Institute of Biomedical Technologies (ITB), Via Fratelli Cervi, 93, 20090 Segrate (MI), Italy.|Fondazione Telethon Piazza Cavour, 1, 20121, Milan, Italy.
authors.forename: Ermanno
authors.initials: E
authors.lastname: Rizzi
authors.affiliation: Metropolitana Milanese S.p.A., Via Giuseppe Meda 44, 20141, Milan, Italy.
authors.forename: Marzia
authors.initials: M
authors.lastname: Bernasconi
authors.affiliation: Institute of Atmospheric Pollution Research, National ResearchCouncil, C/O Physics Department, University of Bari "Aldo Moro", Via Giovanni Amendola, 173 70126, Bari, Italy.|National Research Council (CNR), Institute of Biomedical and Technologies (ITB), via Giovanni Amendola, 122/D, 70126, Bari, Italy.
authors.forename: Saverio
authors.initials: S
authors.lastname: Vicario
authors.affiliation: University of Milan-Bicocca, ZooPlantLab, Biotechnology and Biosciences Department, Piazza della Scienza 2, 20126, Milan, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Galimberti
authors.affiliation: University of Milan-Bicocca, Medicine and Surgery Department, Via Cadore 48, 20126, Monza, Italy.
authors.forename: Clementina
authors.initials: C
authors.lastname: Cocuzza
authors.affiliation: University of Milan-Bicocca, ZooPlantLab, Biotechnology and Biosciences Department, Piazza della Scienza 2, 20126, Milan, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Labra
authors.affiliation: University of Milan-Bicocca, ZooPlantLab, Biotechnology and Biosciences Department, Piazza della Scienza 2, 20126, Milan, Italy.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Casiraghi
mesh_terms: D001419:Bacteria / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification; D044822:Biodiversity; D002244:Carbon / Q000737:chemistry; D002606:Charcoal / Q000737:chemistry; D060766:Drinking Water / Q000382:microbiology*; D005374:Filtration / Q000295:instrumentation / Q000379:methods; D060587:Groundwater / Q000382:microbiology*; D006801:Humans; D007558:Italy; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics*; D014871:Water Microbiology; D018508:Water Purification / Q000295:instrumentation / Q000379:methods; D060753:Water Quality
chemical_list: D060766:Drinking Water; D012336:RNA, Ribosomal, 16S; D002606:Charcoal; D002244:Carbon