Duke University researchers have discovered a basic but surprising fact:Your kitchen sponge is a better incubator for diverse bacterial communities than a petri dish in a lab. But it's not just the trapped leftovers that make the plethora of microbes swarming around so happy and productive, it's the structure of the sponge itself.
In a series of experiments, the scientists show how different microbial species can influence each other's population dynamics, depending on factors of their structural environment, such as complexity and size. Some bacteria thrive in a diverse community, while others prefer a solitary existence. And a physical environment in which both species can live their best lives leads to the strongest levels of biodiversity.
Soil offers this kind of optimal mixed living environment, and so does your kitchen sponge.
Duke biomedical engineers say their results suggest that structural environments need to be considered by industries that use bacteria to perform tasks such as cleaning up pollution or producing commercial products.
Bacteria are like people living through the pandemic — some find it hard to be isolated, while others thrive," said Lingchong You, a professor of biomedical engineering at Duke. “We have shown that in a complex community with both positive and negative interactions between species, there is an intermediate degree of integration that will maximize overall coexistence.”
Microbial communities intermingle in nature to varying degrees. The soil provides many nooks and crannies for different populations to grow without much interaction from their neighbors. The same can be said for individual droplets of water on the tips of leaves.
But when people put many bacterial species together into a structureless mess to produce raw materials like alcohol, biofuel and medicines, it's usually on a plate or even a large barrel. In their experiments, You and his lab show why these industrial efforts might be wise to take a structural approach to their manufacturing efforts.
The researchers coded about 80 different strains of E. coli so they could track their population growth. They then mixed the bacteria in various combinations on lab growth plates with a wide variety of potential living spaces, ranging from six large wells to 1,536 small wells. The large wells approximated environments in which microbial species can mingle freely, while the small wells mimicked spaces where species could co-exist.
Regardless of habitat size, the results were the same. The small wells that started with a handful of species eventually evolved into a community with only one or two tribes remaining. Likewise, the big sinks that started with a wide range of biodiversity also ended the experiment with only one or two species left.
“The small portions really hurt the species that rely on interactions with other species for survival, while the large portions eliminate the members who suffer from these interactions (the loners)," You said. “But the intermediate portions allowed for maximum diversity of survivors in the microbial community.”
The results create a framework for researchers working with diverse bacterial communities to begin testing which structural environments might work best for their pursuits. They also point out why a kitchen sponge is such a useful habitat for microbes. It mimics the varying degrees of separation found in healthy soil, providing different layers of separation in combination with different sizes of common areas.
To prove this, the researchers also did their experiment with a strip of regular household sponge. The results showed that it is an even better incubator of microbial diversity than any lab equipment they have tested.
“It turns out that a sponge is a very simple way to implement multi-level servings to improve the overall microbial community,” You said. “Maybe that's why it's such a dirty thing – the structure of a sponge is just a perfect home for microbes.”
