Bio-active Walls and Concrete Healed by Bacteria: The Promise of Microbes in the Built Environment

by Dr. Bradley van Paridon - October 9, 2019

By Dr. Bradley van Paridon
Photo Credit: by Dr. Bradley van Paridon

Microbes are often treated solely as things that will make us sick and which need to be removed. We spend large amount of time and money disinfecting and cleaning surfaces to rid them of the “microbiome of the built environment”. Now, we are learning more and more about ‘who’ these organisms are and what exactly they do—and this is leading to questions about which microbes need to go and which can stay. This new research frontier covers a wide spectrum of our built world, from our ancient historical buildings to the modern architecture of the future.

Old buildings often have a certain rustic charm stemming from small imperfections accumulated over time. Along with weathering and erosion, the process of bio-deterioration – changes made to a structure by the natural processes of microbes – are responsible for this aging process. Fungi, bacteria and lichens are just a few of the culprits and although the process is natural—think decomposition that occurs in the forest or your composter—it is very destructive to museum artifacts, historic buildings and even modern works of art.

One of the main things responsible for bio-deterioration is a group of microbes known as halophilic organisms. These guys love to feed on salty deposits left on structures when water evaporates off the surface. Thankfully, we have increased our understanding of which types of halophilic organisms reside on buildings and the aesthetic and structural damage they are causing due to advancements in microbiome sampling and DNA sequencing. What we do with this information, though, isn’t yet clear.

In the context of preserving historical buildings, the question is to treat or not to treat? Two major problems exist when considering treatment options. First, are the treatment options safe to use in terms of human health and the integrity of the work being treated? While we have a number of approved fungicidal and bactericidal products, very few of them have been tested as to their long term effects on historical structures or artifacts. Second, we now know that the microbiomes, whether they are on people or buildings, are diverse communities of organisms—meaning a single treatment option will not be effective on all target organisms. This could lead to selection for treatment resistant microbes and a shifting of the balance of the microbiome, further exacerbating bio-deterioration and treatment challenges. This is a relatively new area of research so restoration and preservation specialists unfortunately do not have much history to draw from, unlike the ancient works they are attempting to save.

Along with historical buildings and valued cultural artifacts microbes also have an appetite for our more recent creations too. Concrete is one of the most commonly used building materials, involved in the construction of everything from sewers to bridges and overpasses. The environment of sewers and pipes makes them particularly vulnerable to a plethora of erosive microbes and concrete in general is prone to cracking. This cracking is a serious problem and while some microbes are responsible for causing the problem we are also finding microbes that can help “heal” our vital concrete infrastructure. An innovative new solution using bacteria species from the genus Bacillus aims to “heal” small cracks in concrete before they grow and require more costly repairs. Bacillus bacteria are proving to be surprisingly effective concrete healers due to their ability to precipitate calcium carbonate as they go about their normal activities of consuming urea. When these bacteria are set loose in concrete the calcium carbonate they produce fills in the cracks. Test have so far shown the ability of the bacteria to seal gaps as large as 1mm. Even better still, these bacteria can lay dormant for up to 200 years within concrete and come to life when a crack opens, exposing them to water. Work is still underway to optimize the delivery system of these bacterial repair workers, but the ability to avoid costly concrete deterioration requiring expensive patching or replacement of entire structures will not only save infrastructure dollars, it will also help reduce carbon emissions. As of 2014 concrete production accounted for roughly 9.5% of global emissions so any way we can reduce our need for new concrete is a welcome innovation.

The microbiome of our built environment is also having an impact on human health. According to some estimates, people in the developed world spend up to 90% of their time indoors and we are just now beginning to realize how the microbiomes of these spaces affect us. Health agencies are, in the last ten years, starting to recognize and address what is being called sick building syndrome (SBS). SBS occurs when occupants of building display a range of symptoms associated with time spent in a specific building or room and a building’s microbiome made up of bacteria, mold, fungi and viruses may be partly to blame. Although we invest lots of money into air filtration, cleaning and climate control systems to increase air quality, sanitation and comfort, we may also be creating an unhealthy microbial environment. Our enhanced understanding of the microbiome of buildings means we can better design our living and work spaces to optimize this environment. The concept of “bio-active” walls and carpets is one way in which designers feel a healthy microbial environment can be maintained. Bio-active surfaces are made of permeable nanoparticles seeded with healthy microbes that provide health benefits and out-compete harmful microbes, denying them a place to gain a foothold and spread. Designing new filtration systems for both air and water and even incorporating plants into these is another way in which a healthy building microbiome could be promoted.

We are awakening to the reality that we are just one part of a complex and unseen tapestry of organisms and that our actions greatly influence how this mosaic looks, for better or worse. With greater understanding, though, comes a better ability to manage and therefore live harmoniously with the microbiome of our surroundings—something that will not only improve our health but protect and enhance our built environment.


Dr. Bradley van Paridon is a writer and science communicator who holds a PhD in Parasitology.

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