Size matters, or what I learned from collaborating with environmental engineers

The Sloan Foundation recently convened grantees for the 2^nd Conference on the Microbiology of the Built Environment, and the opening talk focused on the benefits of collaboration. Carlos Rodriguez reminded us (I’m paraphrasing), “When you look at problems in silos, you find solutions in silos. But when you look at problems across disciplines, you find solutions that bridge specialties.”

The talk got me thinking about what I have personally learned in my postdoc position on a project that assembled fungal and bacterial biologists, environmental engineers, chemists, and architects to collaboratively address questions on microbes and microbial products in the indoor environment. When you get your hands greasy with the nuts and bolts of collaborative research, what does that look like? Here’s what it has meant for me.

When we first started to meet together, the trivial barriers to overcome (“Should we meet in our building or yours? Wait, where is the engineering building?”) were soon replaced with more substantial issues. From the ecological side, we wanted to survey the microbial components of indoor dust in a replicated setting, so we proposed an air-sampling scheme that allowed for simultaneous collection of many air samples in a number of apartments over a period of several weeks. Sounds complicated, right? The “sampler” was simply an empty, plastic petri dish hanging from the ceiling, the surface of which I would swab and analyze for the microbial assemblages.

The engineers immediately brought up an issue I hadn’t worked out: what about the particle size of microbial products? Would these samplers only be collecting particles of a certain size due to the dynamics of small particles in air? I’ve come to learn that the sizes of particles and how those sizes affect their movement (for example, their penetration into buildings or lungs and the rate at which they deposit onto surfaces) are fundamental components of research for environmental engineers. While the passive sampler met the requirements from the ecological side of the research collaboration, it still had to prove itself to the engineers.

I set out to test this potential bias in the sampling apparatus with a simple experiment. I placed two samplers side-by-side at three different heights in a room for a month, and then I compared the fungal composition in the different samples within that single room at different heights to the composition in ceiling-hung samplers across different rooms. I had to rely on the help of a colleague without pets or kids, two forces of nature that view the low-hanging dishes as target practice or chew toys (I don’t have pets but the latter is still a problem).

I found that the samplers placed near the ceiling and the floor gave similar snapshots of the fungal composition in the room. So, while the movements of microbial products in air are affected by their sizes, over the course of a month the same type of microbes are getting to different areas of the room.  Over the long-term, Alice of Wonderland shrinking and growing, shrinking and growing, experiences the same fungal communities no matter her height.

All this is an example to show what took me a little while to fully grasp: true collaborations may take longer than research imbedded within one disciple. The reason, unsurprisingly, is related to communication.

When trained in a single field, as I was in ecology, you have a sense of the pressing issues, and you know why those unresolved issues are important to tackle. These lessons you take years to learn — and glossed over when talking to colleagues in the field — typically have to be communicated explicitly and succinctly to your collaborations in other fields when undertaking inter-disciplinary research. Even when you move beyond the background and are actually digging into the science, you may need to spend more time providing context. For example, reading a data figure in your area of expertise is generally straightforward, such that you can see the result — and implications — pretty quickly. When our collaborative research group would get together, we could have practically funded our own research if we got a quarter each time it was said, “Can you walk me through this figure?”

Here is what I’ve learned as a way for me, a biologist, to, one, improve my own science, and two, to make my work potentially informative for environmental engineers focused on indoor air.

1. Mass-balance. Environmental engineers seem to understand processes that structure their system by tracking the mass of particles through space, confirming that the input equals the output (for example, the mass of particles entering a room equal the mass that exits or settles out). Biomass is not something typically measured in microbial ecology studies; rather, we focus on the “what” rather than the “how much.” While the imprecision of methods for detecting abundance in environmental samples undoubtedly explains some of the hesitation, we could infer more about ecological processes by factoring in this parameter.

2. Methods and sampling. Engineers who work on the indoor environment devote a lot of time and energy into quantifying uncertainties in their methods. Biologists recognize that certain uncertainties in their methods exist (for example, we know that the genomic DNA extraction method and bioinformatic processing can affect the identity of the microbial taxa that are detected in samples). But working with engineers have inspired me to think of studies we could do to quantify some of these uncertainties in a way that could then be incorporated more easily into the results and conclusions of a typical study.

3. The model. It seems to me that the goal of taking all these precise measurements about the nature of the room and building is to generate a model — using an equation — that would then be applicable to other settings. For example, if you are going to look at how the particle concentration in the room is affected by vacuuming, you want that estimate to also be informative in another house where the fan speed of the ventilation system happened to be a little higher. I think my field could benefit from a model, even if it not an equation, that is explicit about when we think the results we are reporting are relevant to other ecological settings.

Working back towards a general description of the benefits of inter-disciplinary research, I think that collaborating closely with engineers has reminded me to challenge the basic assumptions of methods that repeated use might coax a field into taking for granted.  As I move forward in my research, I will think more closely about the deposition and dispersal mechanism for bioaerosols — just as relevant for fungal spores in nature as it is for the health effects of spores indoors.  It’s one kind of bridge between the silos.