(This is a guest post by David Thaler, who is one of the Sloan-funded investigators working on the microbiology of the built environment. The goal is to spark substantive discussion, so please comment below!)
A few thoughts after the Inaugural meeting of Microbiology of the Built Environment Boulder
My own opinions on these points are strong but to quote C. Wright Mills “I have tried to be objective, I do not pretend to be detached.”
1. There seems a tension between defining the incipient new field as limited to indoor air and surfaces of buildings or considering the entire city is the built environment.
My sense is that the entire city and transport systems between them are the “built environment”. The point that humans spend 90% of their time indoors is subservient to the fact that most of us spend 99.99% of our time in the “built environment”. If our clothes also constitute part of the built environment then the number is higher. Count the precious moments you have been naked in nature. (Perhaps our next meeting could allow for that experience which would emphasize how rare it is)
2. Most human-associated microbes are intestinal. I would be interested in estimates but my guess is a range of a million to one, i.e. about a million times more intestinal microbes than all others. It is a hypothesis that remains to be tested but almost certainly true that in a building most of the microbes are in and around the plumbing. If the city as a whole is considered, by hypothesis, most of its microbes are in its sewers.
My opinion is that one has to consider where the majority of microbes in the built environment actually are.
3. From the point of view of quantity of microbes in the built environment the meeting did not consider the vast majority. Why?
In part it may be historical, i.e. the meeting has roots in work for many years on indoor air quality and now microbiology with concerns about aerosol Bio Terror detection and protection. A problem arises when the field is expanded outwards in definition but doesn’t take account of the majority microbes encompassed by the larger definition.
It is not news that there are microbes inside sewer pipes. Is there potentially revolutionary- or at least important and interesting- science to do there? To understand and make a difference to the microbial aspect of the built environment means that the sewers must be taken on.
4. There is a tension or even a paradox between the idea that biomedical research is not the focus but, on the other hand, concern about human health, well being, productivity, and safety are important considerations and justifications.
In my opinion “Microbiology of the Built Environment” should encompass the human microbial output and its consequences for the environment. We should ‘keep the faith’ for fundamental science. Best practices should be encouraged on current knowledge even while articulating and acknowledging its limitations.
I agree that the city and beyond need to be considered for the Sloan-encouraged development of a new (or revised) field or domain of inquiry. I define “building ecology” as encompassing not only buildings but also their occupants and other contents and the larger context of nature and/or the urban environment. The resources available to inform the inquiry from a building science perspective are partially represented on my own web site, http://www.buildingecology.com. Click on the link to IAQ and you will find a long list of additional web pages each with its own long list of resources including the following:
BuildingEcology.com Recommends
Be sure to also visit reach of the specific topics (listed below) for additional resources. Each one represents a whole page of additional resources.
General
Health
Ventilation
Monitoring
Emissions
Sources
Pollutants
Building Materials
VOCs
Chemistry
Mold and Moisture
Laboratories
Organizations
Useful Publications
If you have additional suggestions, please forward them to us at info@buildingecology.com, and we will add them to our web site listings.
Thanks for the post David.
I think that when thinking about the microbial ecology of any environment (built or human) we have to be careful to be clear whether we’re talking about actual numbers of microbes or the diversity of microbes. You’re suggesting that potentially the “majority” of microbes might be in the sewers. That could be true numerically, but may not matter so much if that biomass consists of only a few species. The “health” of a built environment microbiome is likely to be more a function of diversity than just biomass? Particularly if we assume that part of being a healthy microbiome is limiting available niches for pathogens to set up shop.
My ‘two cents’ (and worth about that):
Although you are probably correct that the vast majority of the microbes in a building are found in the sewer system, those microbes are likely to be far less important to the occupants of the homes than the microbes in the air, on surfaces, and in our drinking water. Hopefully, not many of us come into contact with the microbes in sewage water on a regular basis. I would also add that there is an enormous body of literature on sewage microbiology so it is not as if this microbial habitat has been ignored.
Further discussion re responses by Hal Levin, David Coll, and Noah Fierer.
The site Hal edits and his work are really important. I study them and will continue to do so. I also agree on the importance of how ‘a new or revised domain of inquiry’ is defined, delimited, or expanded with relation to others that exist. Thus it might be worthwhile in the future to expand the links to include microbial aspects of pipes in the home and sewage in the city and aspects of human health such as the hygiene hypothesis. A Venn Diagram suggests a way to represent disciplinary overlap but not become diffuse or disoriented by all the links and connections.
David Coll makes important points I want to respond to specifically:
1. I agree that it is essential not to confuse quantity of microbial mass vs species diversity and apologize for fuzzing that point in my initial post. Here is a specific proposal to untangle them: Compare the species lists derived from human fecal biome projects with the species lists derived from other sources in the built environment. How much overlap is there when species depth is high, i.e. data are extensive for each? My sense is that there may be signature species, for example E. coli is used to test for fecal contamination in water samples yet it is not the dominant bacteria in feces. I remember hearing at a previous meeting (sorry i can not recall the speaker’s name) on aerobiology that if you search deeply with molecular methods you will find everything everywhere. Finding a particular species in a particular local does not tell where it comes from or how it got there.
Regarding the ratio of species in a given sample, this might be technically hard depending on how amplification and sequencing are done but is important- since with enough sequencing everything is found everywhere- and worth further discussion.
2. re the cool idea: “The “health” of a built environment microbiome is likely to be more a function of diversity than just biomass?”
I’m with you that it is a great question. Maybe re the hygiene hypothesis exposure to a high diversity of microbes helps the immune system develop optimally. On the other hand, one speculation is that tuberculosis is such a dastardly disease in part because there are lots of non- or much less- pathogenic mycobacteria in the environment (Norman Pace has shown it for the developed world and other species of mycobacteria are also endemic in regions with TB) so perhaps the immune systems gets “comfortable” with mycobacteria and thereby diminishes its attack against the pathogen M. tuberculosis. Immune system being “lulled” may also be a contributor to the sad fact that anti-TB vaccines (BCG) do not work very well.
3. re the important idea: “Particularly if we assume that part of being a healthy microbiome is limiting available niches for pathogens to set up shop.”
This brings up an important weak point, with regard to microbes, in the analogy of a house and a human body. In a healthy human intestine the microbial flora is not just there; it is metabolically active and growing. In the case of a house, David C. raises an important point that there may not be any “good and healthy” surface or circumstance in which microbes are metabolizing and growing in the home.
Perhaps in contrast, microbes are metabolically active in the pipes of homes and sewers of the city.
Noah Fierer raises interesting points:
1. re “Although you are probably correct that the vast majority of the microbes in a building are found in the sewer system, those microbes are likely to be far less important to the occupants of the homes than the microbes in the air, on surfaces, and in our drinking water. Hopefully, not many of us come into contact with the microbes in sewage water on a regular basis.”
Neither biological nor physical systems are perfect in their isolation. If there really are a million times more microbes in the pipes than all other surfaces and air combined it would be hard to preclude cross talk. I will give three examples, two from the literature and one anecdotal. 1) Bruce Levin (1984) and others since have shown that members of a households tend to share intestinal strains. 2) The SARS epidemic (Severe Acute Respiratory Syndrome) was initially spread via plumbing throughout an apartment building in the quite modern and developed city of Hong Kong.
Anecdotally I have had the experience in both home and laboratory of plumbing breaks. My sense is that these spread in a few hours of dripping or a few minutes of gushing more microbes than years of other factors.
I want to bridge from the anecdote to a more general consideration of disaster preparedness and resilience. When plumbing falters in a building it quickly becomes apparent where the majority of human-microbial interaction is. http://www.ready.gov/document/are-you-ready-depth-guide-citizen-preparedness
anticipates and recommends to prepare for sewage interruption for days or longer. I think that their recommendations while not inconsistent with the best current knowledge could be improved upon with more microbiological understanding.
In summary- and this deserves a more extended discussion- my sense is that interpersonal human fecal biome interactions are part of normal households and building microbiology no matter how clean you think you are and they have the potential to become drastically more intense at any moment.
2. Noah make the point “I would also add that there is an enormous body of literature on sewage microbiology so it is not as if this microbial habitat has been ignored.”
I agree there is a literature on sewage microbiology and do not mean to slight it. I suggest the need to bridge and incorporate this literature into the incipient field of “Microbiology of the Built Environment”. I think the field “Microbiology of the Built Environment” will create a “King without his cloths” problem if it tries to ignore where 99.++?% of the microbes in its defined domain actually are. The differential is likely to be even larger when considering microbial metabolic activity rather than mere presence.
Despite a large literature I think there is a lot more to learn and the possibility of qualitative changes in human-microbial interactions that could arise from a deeper understanding of the transformations and consequences of the human fecal microbiome after it has left the body.