Roommates are all about chemistry, molecularly speaking

In and on every human being are 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.

Writing in the June 24, 2022 issue of: scientific progressScientists at the University of California San Diego School of Medicine and elsewhere report on the molecular impact of living indoors, describing how the presence of humans interacts with their microbial roommates, altering the biology and chemistry of the home.

The findings, the authors suggest, should influence future building designs.

Modern Americans spend about 70 percent of their time indoors, reshaping the microbiome indoors with input from their bodies. Limited research has examined the interaction between people and indoor exposure to specific pollutants, toxins and particles, but the new study more ambitiously documents how people affect the entire molecular and chemical makeup of a home through routine activities.

In the summer of 2018, an experimental test house was built in Austin, Texas. The house was designed for ordinary use and included bathrooms, a kitchen, gathering and work areas. Overnight stays were prohibited, but 45 study participants, plus visitors, spent time in the house, about six hours a day for 26 days, performing scripted activities such as cooking, cleaning and socializing.

Researchers have examined the distribution of detectable molecules and microbes in the occupied parts of the house at the beginning of the experiment, called T1, and again 28 days later, called T2, largely by wiping surfaces and performing various genomic, metabolic and chemical analyses.

For T1, the house was thoroughly cleaned with a bleach solution. Nevertheless, researchers said traces of molecules associated with humans were still present. At T2, after nearly a month of human habitation, the house was alive with molecular and microbial abundance and diversity, albeit unevenly.

Researchers have found molecules related to skin care productsskin cells, drugs (such as antidepressants and anabolic steroids), food-derived molecules (such as terpenes and flavonoids), human or animal metabolites (molecules generated during metabolism, such as bile and fatty acids), amino acids, sugars and microbial metabolites.

Most of the molecules on the inner surface were natural products (biologically produced molecules rather than synthetic compounds), food, molecules related to the outdoors, personal care products, and human-derived metabolites, often traceable to fecal matter.

Food, human-associated microbes, feces, construction materials and the microbes growing on it and building materials in moist conditions were considered the likely primary sources.

Not surprisingly, the kitchen and restroom were hot spots of molecular and microbial diversity, though the number fluctuated with surface cleaning and sanitation. “It seems that even when some of the chemistry is removed due to the cleaning, it is only temporary and/or partial, as the sum of the cleaning and human activities in general results in an increase in the accumulation of richer chemistry said the authors. wrote.

Surfaces routinely touched by humans, such as tables, light switches and knobs, were more abundant in molecular and microbial chemistry. Floors showed less molecular diversity, perhaps because they were cleaned more often. Windows, seats and doors not routinely touched by human residents showed the least change in chemical diversity between T1 and T2.

other residents

Of course, the people were not the only inhabitants of the test house. Researchers found interior surfaces covered in bacteria, fungi and other microbes, plus their metabolites. Regular cleaning changed these microbial populations and diversity over time, allowing different species to recolonize cleaned spaces.

At the end of the test period, less than half of the home’s original microbiome was left, but this accounted for more than 96 percent of all microbial life counted. Most of the microbiome detected at T2 came from human inhabitants, mainly commensal species living on human skin or in the gut. Free-living, environment-related microbes had been depleted by human activities. In other words, cleaned or pushed out.

“We don’t know exactly how the human-related microbes squeezed the microbes out of the environment, because there are many ways this can happen, but it’s clear they do,” said Rob Knight, Ph.D., a researcher. of the study’s principal investigators. and director of the Center for Microbiome Innovation at UC San Diego. “Understanding this phenomenon will be an important goal of future research into the microbiology of the built environment.”

The authors noted that at least 1 percent of the molecules detected indoors may have an excessive health effect. For example, the bacterial species Paenibacillus was associated with molecules from coffee, one of the dominant sources of detected indoor food-derived molecules. At home, especially at T2, Paenibacillus was observed in and around the area where coffee was prepared and the genus was found to grow in coffee machines. Paenibacillus species have been used as probiotics in chickens and bees, and may also contribute to human health, consistent with: recent reports that drinking coffee is associated with improved cardiovascular health and longer life.

“In particular, understanding how our observations that both human and microbial inhabitants change the chemical makeup of a home should influence the design of building materials to improve human health additional studies,” said co-principal investigator Pieter Dorrestein, Ph.D., director of the Collaborative Mass Spectrometry Innovation Center at the Skaggs School of Pharmacy and Pharmaceutical Sciences at UC San Diego.