About a recent paper from my lab: Deepika Sundarraman, T. Jarrod Smith, Jade V. Z. Kast, Karen Guillemin, and Raghuveer Parthasarathy, “Disaggregation as an interaction mechanism among intestinal bacteria,” Biophysical Journal (2022).
Some bacteria stick together; others do not. We have seen these variations among bacteria inside the zebrafish gut, and it’s probably the case for your gut bacteria as well. Over the past few years we’ve uncovered connections between the aggregation of gut bacteria and all sorts of phenomena from responses to antibiotics to interactions with the immune system. In this paper, we report a surprising new aspect of bacterial aggregation: disaggregation.
The main character is a bacterial species we’ve looked at before. It forms dense clusters in the zebrafish gut, and it forms clusters in a test tube. (It’s generally not the case that bacteria do the same thing in a test tube as in the gut, but this one does.) Our collaborator Jarrod Smith, a postdoc in the lab of Karen Guillemin, created/discovered a variant of this species that, if a particular sugar is present, doesn’t form test-tube aggregates. That sugar is a common component of intestinal mucus, and we found that the mutant bacteria doesn’t aggregate inside the intestine of living fish.
The surprising part was what we found when we introduced the mutant to zebrafish whose guts were already occupied by a different bacterial species, a species that’s the most aggregated of all the ones we’ve looked at. (Well over 90% of the bacteria are in dense, three-dimensional clusters.) These aggregates fell apart, disintegrating into individual bacteria within tens of minutes! The non-aggregating mutant, in other words, induced a different species to dis-aggregate.
Thanks to our collaborators, we know the mutation involved (a separate story; link) and we have a rough idea of how this disintegration may be occurring. In our paper, though, we simply focus on the phenomenon itself, and what happens when still more species are present. It’s not the full story, which will take a lot more effort to figure out, but we’re nonetheless excited to have discovered a previously unrealized way for gut bacteria to interact and compete: manipulation of each other’s aggregation state. One might imagine that this could lead to strategies for deliberately altering gut microbiome composition.
There’s a whole chapter on gut microbes, by the way, in my pop-science biophysics book. The usual links: My description, Publisher, Amazon.)
Today’s illustration
I thought I’d try something schematic to illustrate dis-aggregation. Watercolor isn’t the best medium for this sort of illustration, which should be flatter and more stylized.
— Raghuveer Parthasarathy; September 4, 2022
The Eighteenth Elephant 