Spontaneous body wall contractions stabilize the fluid microenvironment that shapes host-microbe associations

Abstract

The freshwater polyp Hydra is a popular biological model system; however, we still do not understand one of its most salient behaviours, the generation of spontaneous body wall contractions. Here, by applying experimental fluid dynamics analysis and mathematical modelling, 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.

Novel technologies uncover novel ‘anti’-microbial peptides in Hydra shaping the species-specific microbiome

“…They not only regulate the density of the bacterial communities a healthy polyp harbours (so called carrying capacity; [74]) but also control the composition of these communities. As a result, certain species of bacteria, such as Pseudomonas , Flavobacterium and Acidovorax , are confined to the lower part of the Hydra polyp and virtually absent from the hypostome [75]. On the contrary, other members of the microbiome such as Curvibacter [11,76], are found more abundantly on the polyp's head and tentacles.…”