Spontaneous body wall contractions stabilize the fluid microenvironment that shapes host–microbe associations
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eLife assessment
This important work studies the spontaneous contractions (SC) of the Hydra body wall and presents a mathematical model of nutrient transport to hypothesize the role of SC on maintaining the microbiota. The solid evidence presented yields insights on the functional implications of the SC and the increased nutrient update obtained from mixing the local fluid environment through body wall contractions. The main result represents an important observation about the role of hydrodynamics on organism behavior and its relation to diffusive chemical transport processes.
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Abstract
The freshwater polyp Hydra is a popular biological model system; however, we still do not understand one of its most salient behaviors, the generation of spontaneous body wall contractions. Here, by applying experimental fluid dynamics analysis and mathematical modeling, we provide functional evidence that spontaneous contractions of body walls enhance the transport of chemical compounds from and to the tissue surface where symbiotic bacteria reside. Experimentally, a reduction in the frequency of spontaneous body wall contractions is associated with a changed composition of the colonizing microbiota. Together, our findings suggest that spontaneous body wall contractions create an important fluid transport mechanism that (1) may shape and stabilize specific host–microbe associations and (2) create fluid microhabitats that may modulate the spatial distribution of the colonizing microbes. This mechanism may be more broadly applicable to animal–microbe interactions since research has shown that rhythmic spontaneous contractions in the gastrointestinal tracts are essential for maintaining normal microbiota.
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eLife assessment
This important work studies the spontaneous contractions (SC) of the Hydra body wall and presents a mathematical model of nutrient transport to hypothesize the role of SC on maintaining the microbiota. The solid evidence presented yields insights on the functional implications of the SC and the increased nutrient update obtained from mixing the local fluid environment through body wall contractions. The main result represents an important observation about the role of hydrodynamics on organism behavior and its relation to diffusive chemical transport processes.
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Reviewer #1 (Public Review):
The manuscript studies the spontaneous contractions (SC) of the Hydra body wall and presents a detailed simple mathematical model of nutrient transport to hypothesize the role of SC on maintaining the microbiota. This work provides valuable insights on the functional im- plications of the SC and the increased nutrient update obtained from mixing the local fluid environment through body wall contractions.
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Reviewer #2 (Public Review):
The authors examine the transport of chemical compounds from a surrounding fluid environment to the surface of the polyp Hydra. They propose that spontaneous contractions of the body, which are known to occur roughly three times per hour, provide a new fluid environment near the body surface and thereby increase the total rate of compound uptake. Experimental measurements and a mathematical model are used to support the main claim. Active probes of the system involve the use of ion channel inhibitors, which can affect the frequency of contractions. But there is a useful feature of Hydra already present which the authors also use for a comparative study, namely the different microbial environments near the Hydra's motionless foot and near its moving head. The evidence which is provided puts the claim on solid …
Reviewer #2 (Public Review):
The authors examine the transport of chemical compounds from a surrounding fluid environment to the surface of the polyp Hydra. They propose that spontaneous contractions of the body, which are known to occur roughly three times per hour, provide a new fluid environment near the body surface and thereby increase the total rate of compound uptake. Experimental measurements and a mathematical model are used to support the main claim. Active probes of the system involve the use of ion channel inhibitors, which can affect the frequency of contractions. But there is a useful feature of Hydra already present which the authors also use for a comparative study, namely the different microbial environments near the Hydra's motionless foot and near its moving head. The evidence which is provided puts the claim on solid footing. The main result represents an important observation about the role of hydrodynamics on organism behavior, in particular in its relation to diffusive chemical transport processes.
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