In “End of the Anthropocene,” an article published in Sci-Arc’s Offramp journal a few years ago, architecture professor Ted Krueger describes the recent discovery of a planet dominated by over a trillion species of terraforming life forms. These earth-shaping organisms not only exert control over the planet’s geology but also its atmosphere and hydrosphere. Where is this celestial body? “You’re living on it,” writes Krueger. “The terraformers are microorganisms.”

Krueger is an associate professor and graduate director at the Rensselaer Polytechnic Institute School of Architecture; he studies the microbiome and its influences within buildings. In “Microecologies of the Built Environment,” a chapter that he authored in The Routledge Companion to Biology in Art and Architecture (2019), Krueger argues that architecture’s conventional focus on the human scale should expand to include the microbial scale: “The growing realization of the spectacular diversity of phyla, species, and strains of micro-organisms and their ubiquity, and even more so, the deep interrelationship between humans and microbes, demands that designers also become aware of these relationships and begin to use them as positive assets in their configuration of the world.”

In recent decades, scientists have discovered surprising facts about microorganisms’ influence on human and planetary health. Research programs such as The Human Microbiome Project have revealed the extent to which bacteria and other organisms are a fundamental part of human anatomy. For example, each of us carries between two and six pounds’ worth of bacteria that outnumber our own cells by a factor of 10. This may be unsettling news, given our current obsession with sanitation and antimicrobial treatments. But these bacteria provide many critical health benefits related to digestion, vitamin production, and the fighting of illness. According to the HMP website: “An ever-growing number of studies have demonstrated that changes in the composition of our microbiomes correlate with numerous disease states, raising the possibility that manipulation of these communities could be used to treat disease.”

For Krueger, such manipulation can extend beyond the human body, since our microbiomes are connected to the microecologies in our buildings. “A fog of particles containing micro-organisms surrounds us and follows us through our daily activities,” he writes in the Routledge Companion. As we now know from coronavirus transmission studies, we share microbes with our surroundings when we sneeze, talk, cough, and so on. We also slough-off skin and hair cells throughout the day. Building occupants come into contact with these micro-ecologies by stirring up dust particles, touching microbe-covered surfaces, or breathing in organisms suspended in the air. This can lead to illness—as seen with Legionnaire’s disease, sick-building syndrome, and COVID-19. But not all building microecologies are bad. In fact, beneficial microbes are often more desirable than sterile spaces.

Krueger argues that architects should operate more like creative chefs than forensic doctors, manipulating conditions to encourage the cultivation of healthy microbiota.

One welcome setting for a healthy microecology is a food-processing facility—particularly one where fermentation or similar techniques are involved. Krueger offers the example of artisanal cheese-making, which relies on functional microbiota that influence the character of the food produced. In other words, these facilities contain their own “house” microecologies that fundamentally affect the qualities of the cheese. Discovered in recent years, this phenomenon reveals that interior environments have a more significant influence on foodmaking processes than previously understood—a realization that merits further study. “This new understanding of the role of the microbial environment suggests that, perhaps soon, house microecologies will be designed through the selection of materials, conditions, spatial configurations, and inoculations,” Krueger writes in the Routledge Companion. He argues that architects should operate more like creative chefs than forensic doctors, manipulating conditions to encourage the cultivation of healthy microbiota. “Currently we try to exclude other species [in buildings],” he says. “Then, we go camping on the weekend in 'nature’ because we feel renewed by the contact with the species we have eliminated.” Instead, architects should develop multi-scale, multi-species design criteria that enable us to co-exist with other organisms.

Another area of growing interest in the study of microecological function is the fighting of disease. Just as the human biome plays a role in protecting the body from illness, architectural microbiota are known to be capable of preventing pathogen transmission. Microbial mats are used for water filtration, for example. Interior plant-based phytoremediation is also used to purify indoor air. More research is required, however, to understand the potential for building microecologies to fight disease transmission. Krueger suggests that "understanding how pathogens exist in and move through environments could have immediate applications in how we design indoor environmental systems.” Typical HVAC systems, for example, are very efficient in moving microbes between individuals. These systems should be redesigned to direct pathogens away from us by using some form of microbe-activated filtration media—an element that could be critical for mitigating the spread of the coronavirus. “The changes we make in response to COVID might well make the environment a better one for resisting the common colds or the flu,” Krueger adds.

Microbes can also help carry out fundamental building processes. For example, they can be used to construct and repair building materials. Some bacteria create calcium carbonate via bio-mineralization, forming rock while pulling CO2 out of the atmosphere. For example, Durham, N.C.-based Biomason harnesses this natural phenomenon to create pre-cast concrete building modules. “Micro-organisms that deposit carbonates as a function of their metabolic activity have been used to stabilize soils without excavation or other disturbance and can stabilize existing structural materials without the use of applied coatings,” Krueger writes in the Routledge Companion. Microbes can also play a significant role in sewage treatment. Large-scale composting, which breaks down human waste and eradicates pathogens, could replace entire conventional plumbing and sanitation systems. (Last spring, Krueger taught an architecture studio where students designed a composting facility capable of processing the entire human waste of Manhattan.)

Although invisible, the microecology within the built environment has significant potential to enhance human health. An architecture designed to cultivate microbiota would support a kind of small-scale agriculture, or micro-agronomy, that could benefit human occupants and other species. “I expect that there are changes to the indoor environment that might foster a cooperative community, shifts in material and the geometries of their surfaces at a microscopic scale, adjustments to acidity, humidity, and airflow,” says Krueger. Although we may not be able to perceive surfaces or systems that support the growth of diverse microbial communities, we would appreciate the benefits they might provide, much in the way that the bacteria-powered phytoremediation that takes place within the root systems of plants is invisible, yet we appreciate the plants themselves. “We appreciate the oxygen they supply, the acoustic properties they bring to the space, the smells that they might offer us, and the opportunity that they create for birds or pollinators,” says Krueger. “Positive experiential benefits might accrue from an effort that is operating at an invisible scale."