Tap water as a natural vehicle for microorganisms shaping the human gut microbiome

Fresh potable water is an indispensable drink which humans consume daily in substantial amounts. Nonetheless, very little is known about the composition of the microbial community inhabiting drinking water or its impact on our gut microbiota. In the current study, an exhaustive shotgun metagenomics analysis of the tap water microbiome highlighted the occurrence of a highly genetic biodiversity of the microbial communities residing in fresh water and the existence of a conserved core tap water microbiota largely represented by novel microbial species, representing microbial dark matter. Furthermore, genome reconstruction of this microbial dark matter from water samples unveiled homologous sequences present in the faecal microbiome of humans from various geographical locations. Accordingly, investigation of the faecal microbiota content of a subject that daily consumed tap water for 3 years provides proof for horizontal transmission and colonization of water bacteria in the human gut.

Density-dependent microbial calcium carbonate precipitation by drinking water bacteria via amino acid metabolism and biosorption

Drinking water plumbing systems appear to be a unique environment for microorganisms as they contain few nutrients but a high mineral concentration. Interactions between mineral content and bacteria, such as microbial calcium carbonate precipitation (MCP) however, has not yet attracted too much attention in drinking water sector. This study aims to carefully examine MCP behavior of two drinking water bacteria species, which may potentially link scaling and biofouling processes in drinking water distribution systems. Evidence from cell density evolution, chemical parameters, and microscopy suggest that drinking water isolates can mediate CaCO₃ precipitation through previously overlooked MCP mechanisms like ammonification or biosorption. The results also illustrate the active control of bacteria on the MCP process, as the calcium starts to concentrate onto cell surfaces only after reaching a certain cell density, even though the cell surfaces are shown to be the ideal location for the CaCO₃ nucleation.

Microbiomes and chemical components of feed water and membrane-attached biofilm in reverse osmosis system to treat membrane bioreactor effluents

Reverse osmosis (RO) system at a stage after membrane bioreactor (MBR) is used for the wastewater treatment and reclamation. One of the most serious problems in this system is membrane fouling caused by biofilm formation. Here, microbiomes and chemical components of the feed water and membrane-attached biofilm of RO system to treat MBR effluents were investigated by non-destructive confocal reflection microscopy, excitation-emission fluorescence spectroscopy and high-throughput sequencing of 16S rRNA genes. The microscopic visualization indicated that the biofilm contained large amounts of microbial cells (0.5 ± 0.3~3.9 ± 2.3 µm³/µm²) and the extracellular polysaccharides (3.3 ± 1.7~9.4 ± 5.1 µm³/µm²) and proteins (1.0 ± 0.2~1.3 ± 0.1 µm³/µm²). The spectroscopic analysis identified the humic and/or fulvic acid-like substances and protein-like substances as the main membrane foulants. High-throughput sequencing showed that Pseudomonas spp. and other heterotrophic bacteria dominated the feed water microbiomes. Meanwhile, the biofilm microbiomes were composed of diverse bacteria, among which operational taxonomic units related to the autotrophic Hydrogenophaga pseudoflava and Blastochloris viridis were abundant, accounting for up to 22.9 ± 4.1% and 3.1 ± 0.4% of the total, respectively. These results demonstrated that the minor autotrophic bacteria in the feed water played pivotal roles in the formation of polysaccharide- and protein-rich biofilm on RO membrane, thereby causing membrane fouling of RO system.