Unlike their ancestors, modern humans spend most of their time indoors—in offices, homes, schools, and other built environments. These spaces are also where people encounter most of their microbial exposure. Erica Hartmann, an environmental microbiologist at Northwestern University, studies the teeming microbial diversity from bacteria to bacteriophages in these spaces and uses these insights to manage built environments in ways that could enhance human health.
Bathrooms, with their damp conditions, are ideal for microbial growth. Previously, Hartmann and her colleagues collected samples from volunteers across the United States to characterize the bacterial diversity in frequently wet bathroom staples, such as showerheads and toothbrushes.1,2 Showerhead microbiomes differed by their geographical location and type of water source (public or well). In contrast, toothbrushes harbored bacteria that reflected the human oral microbiome.
These microbial towns are also home to bacteria’s nemeses: bacteriophages. These viruses, which hunt down bacteria, show potential in treating antibiotic-resistant bacterial infections. This inspired Hartmann to take a closer look at the bacteriophages that inhabit these bathroom biomes.
“We turned our blinders from bacteria and their functions to bacteriophages and who they might be interacting with,” said Hartmann. She added, “Phages, in the grand scheme of biology, are one of the least understood aspects of microbiology.”
In a paper published in Frontiers in Microbiomes, Hartmann and her team revealed that showerheads and toothbrushes house more than 600 different bacteriophages.3 Their findings highlight the bacteriophage diversity that may shape microbial communities and provide insights into how leveraging these interactions could benefit human health.
To better understand phage-bacteria interactions, the researchers returned to their showerhead and toothbrush samples, this time to explore the viruses living amongst the sampled biofilms—sticky, glue-like communities of microbes that attach to surfaces.1,2 Hartmann and her team used metagenomic sequencing to home in on the biofilms’ viral neighbors. The results excited Hartmann: They identified 614 different viruses, classified as viral operational taxonomic units (vOTUs), with each sample containing a unique combination of bacteriophages. While the viromes of showerheads and toothbrushes were distinct from each other, Hartmann found minimal overlap in vOTUs between any two samples. This sharply contrasted with their earlier research on bathroom bacteria, where most samples exhibited a considerable degree of microbial similarity. However, they did observe a few viral interactions that occurred with bacterial families, such as Pseudomonadaceae and Burkholderiaceae.
“It just underscores that the amount of microbial diversity out there is awesome, and the amount of phage diversity is another degree of magnitude or several greater, which is kind of mind-blowing,” Hartmann remarked.
However, the researchers also identified a notable pattern with mycobacteriophages, which infect Mycobacterium, one of the most abundant microbes found in residential showerheads.4 Most of the detected mycobacteriophages were linked to multiple Mycobacterium. This interaction is noteworthy because inhaling aerosolized Mycobacterium while showering is a mode of transmission in nontuberculosis mycobacterial lung infections.
“I can see a future where we're able to introduce [specific] phages into [the built] structure to allow for controlled ecological dynamics,” said Jack Gilbert, a microbial ecologist at the University of California, San Diego, who was not involved in the study. “You can imagine creating your sink plumbing out of biologically alive materials and integrating viral ecology in there to ensure microbial control.” By incorporating certain bacteriophages into plumbing systems, he noted that these curated viral ecosystems could reduce bad smells and curb bacterial pathogens.
While this work only scratches the surface of the virome within the built environment, Hartmann wants to further explore how microbes establish themselves and transfer within these indoor spaces. “I'm really interested in harnessing this information so that we can influence these outcomes and potentially design better products and processes.”
- Webster TM, et al. Structure and functional attributes of bacterial communities in premise plumbing across the United States. Environ Sci Technol. 2021;55(20):14105-14114.
- Blaustein RA, et al.Toothbrush microbiomes feature a meeting ground for human oral and environmental microbiota. Microbiome. 2021;9(32).
- Huttelmaier S, et al. Phage communities in household-related biofilms correlate with bacterial hosts. Front Microbiomes. 2024;3:1396560.
- Gebert MJ, et al. Ecological analyses of mycobacteria in showerhead biofilms and their relevance to human health. mBio. 2018;9(5):e01614-18.
