UCSD Jacobs School of Engineering

From jungle huts to city apartments: how do chemicals and microbes differ?

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San Diego, Calif., Nov. 7, 2019-- Researchers at University of California San Diego, Rutgers and other universities compared microscopic materials in homes and people’s bodies, spanning the spectrum of urbanization in the Amazon basin. 

They found that the diversity of chemicals clinging to indoor surfaces increases dramatically with urbanization. Most notably, they found more fungi, industrial chemicals, cleaning agents and molecules derived from medications in city homes but not in rural or jungle homes.

The study published November 4, 2019 in the journal Nature Microbiology.

The locations studied included a remote Peruvian jungle village of thatched huts with no walls; a Peruvian rural town with wooden houses lacking indoor plumbing; a Peruvian city of 400,000 residents and more modern amenities; and the metropolis of Manaus, Brazil, which has a population of 2 million.

Urbanization is associated with a drop in infectious diseases but also an increase in obesity, asthma, allergies, autism and other disorders, as well as decreased diversity in the human microbiome, the communities of microbes living on and in our bodies.

“We are just now starting to quantify the effect of cutting ourselves off from the natural environment with which we as humans co-evolved and of replacing it with a synthetic environment,” said co-corresponding author Rob Knight, PhD, professor and director of the Center for Microbiome Innovation at University of California San Diego. “What’s next is to identify the specific differences associated with urbanization that have a health impact and to design interventions to reverse them. Those could be anything from knowing how many minutes a week should be spent outdoors in natural environments to air fresheners that are good for the microbiome.”

Although the urban dwellers reported cleaning more frequently, surfaces in their homes had a greater diversity of fungal species associated with human skin. This may be because the fungi have become resistant to cleaning products, the researchers hypothesized. It may also reflect the urban homes’ warmer temperatures, reduced air exchange, lower levels of natural light and higher loads of human skin flakes. 

The researchers also found a greater diversity of foot fungus among the urban dwellers. In the rural and jungle homes, the researchers found a greater variety of bacteria and fungi that live outside, and fewer species known for colonizing the human body.

“Urbanization represents a profound shift in human behavior,” said senior author Maria Gloria Dominguez-Bello, professor at Rutgers University–New Brunswick. “Modern living literally walls us off from the natural environment and shuts us in with industrial compounds, higher carbon dioxide levels and skin-loving fungi.”

Dominguez-Bello said exposure to these various environmental microbes and molecules may influence the makeup of the human microbiome. Her prior research found that people in urbanized societies have lost a substantial part of their microbiota diversity compared with hunter-gatherers in isolated Amazonian villages. It remains to be determined how human microbiome diversity might in turn influence our long-term health.

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