Within and on every human being reside countless microorganisms, the microbiota that help shape and direct the lives of their hosts. A similar phenomenon occurs between people, microbes, and the homes they share.
Written in the June 24, 2022 edition of scientists make progressScientists from the University of California, San Diego School of Medicine and elsewhere report the molecular impact of living indoors, describing how the presence of humans interacts with their microbial housemates, altering the biology and chemistry of the House.
The findings, the authors suggest, should influence future building designs.
Modern Americans spend about 70% of their time indoors, remodeling the indoor microbiome with information from their bodies. Limited research has investigated the interaction between humans and indoor exposures to specific pollutants, toxins, and particles, but the new study more ambitiously documents how people influence the overall molecular and chemical makeup of a home through activities. routine.
An experimental test house was erected in Austin, Texas during the summer of 2018. The house was designed for ordinary use and included bathrooms, kitchen, meeting and work areas. Overnight stays were prohibited, but 45 study participants, as well as visitors, did spend time at the home, occupying it approximately six hours a day for 26 days, during which they engaged in scheduled activities such as cooking, cleaning and socializing.
The researchers sampled the distribution of detectable molecules and microbes in occupied areas of the house at the beginning of the experiment, called T1, and again 28 days later, called T2, largely by rubbing surfaces and performing various genomic, metabolic, and chemical analyses.
Before T1, the house was deep cleaned with a bleach solution. However, the researchers said there were still traces of molecules associated with humans. At T2, after almost a month of human occupation, the house was full of molecular and microbial abundance and diversity, albeit unevenly distributed.
Researchers have found molecules associated with skin care products, skin cells, drugs (such as antidepressants and anabolic steroids), food-derived molecules (such as terpenes and flavonoids), human or animal metabolites (molecules generated during the process of metabolism, such as bile and fats). acids), amino acids, sugars and microbial metabolites.
Most of the inner surface molecules were natural products (biologically produced molecules rather than synthetic compounds), foods, foreign-associated molecules, personal care products, and artificial metabolites, often bound to faeces materials.
Food, human-associated microbes, feces, building materials and the microbes that grow there, and building materials in wet conditions were considered the main likely sources.
As expected, the kitchen and bathrooms were hotspots for molecular and microbial diversity, although the numbers fluctuated with the cleaning and disinfection of surfaces. “It appears that even when a subset of chemicals is removed due to cleanup, it is only temporary and/or partial, as the sum total of cleanup and human activities in general results in a greater accumulation of richer chemicals. “, the authors explain. to written.
Surfaces that people regularly touch, such as tables, light switches and doorknobs, were more abundant in molecular and microbial chemistry. The floors showed less molecular diversity, possibly because they were mopped more frequently. Windows, chairs, and doors that are not routinely touched by human occupants showed the least change in chemical diversity between T1 and T2.
Of course, people weren’t the only occupants of the test house. The researchers discovered interior surfaces covered in bacteria, fungi and other microbes, as well as their metabolites. Regular cleaning changed these microbial populations and their diversity over time, allowing different species to recolonize clean spaces.
At the end of the trial period, less than half of the original home microbiome remained, but it represented more than 96% of all counted microbial life. Most of the microbiome detected in T2 came from human occupants, mainly commensal species that reside on human skin or in the gut. Free-living microbes associated with the environment have been decimated by human activities. In other words, cleansed or expelled.
“We don’t know exactly how human-related microbes wiped out environmental microbes because it could happen in many ways, but it’s clear they do,” said Rob Knight, PhD, one of the study’s principal investigators and director of the Center for Innovation. of the microbiome. at the University of California at San Diego. “Understanding this phenomenon will be a key goal for future research on the microbiology of the built environment. »
The authors noted that as few as 1% of the molecules detected inside can have an outsized effect on health. For example, bacterial species Paenibacillus was associated with coffee molecules, one of the main detected sources of foodborne molecules indoors. At home, especially in T2, Paenibacillus it has been observed in and around the area where the coffee was made and the genus has been found to grow in coffee machines. Paenibacillus they have been used as probiotics in chickens and bees, and may also help human health, according to recent reports that coffee consumption is associated with better cardiovascular health and longevity.
“Specifically understanding how our observations that human and microbial occupants alter the chemical composition of a house should influence the design of building materials to improve human health will require further study,” said co-principal investigator Pieter Dorrestein, PhD. , Director of the Collaborative Center. for Innovation in Mass Spectrometry at the UC San Diego Skaggs School of Pharmacy and Pharmaceutical Sciences.
Coauthors include: Alexander A. Aksenov and Alexey V. Melnik, UC San Diego and the University of Connecticut; Rodolfo A. Salido, Caitriona Brennan, Asker Brejnrod, Andrés Mauricio Caraballo-Rodríguez, Julia M. Gauglitz and Franck Lejzerowicz, Delphine K. Farmer, Colorado State University; and Marina E. Vance, University of Colorado at Boulder.
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