Developing Inside a Layer of Germs—A Potential Role for Multiciliated Surface Cells in Vertebrate Embryos

Abstract

This paper reviews current research on the microbial life that surrounds vertebrate embryos. Several clades are believed to develop inside sterile—or near-sterile—embryonic microhabitats, while others thrive within a veritable zoo of microbial life. The occurrence of embryo-associated microbes in some groups, but not others, is an under-appreciated transition (possibly transitions) in vertebrate evolution. A lack of comparable studies makes it currently impossible to correlate embryo-associated microbiomes with other aspects of vertebrate evolution. However, there are embryonic features that should instruct a more targeted survey. This paper concludes with a hypothesis for the role of multiciliated surface cells in amphibian and some fish embryos, which may contribute to managing embryo-associated microbial consortia. These cells are known to exist in some species that harbor in ovo microbes or have relatively porous egg capsules, although most have not been assayed for embryo-associated microbiota. Whether the currents generated within these extraembryonic microhabitats contribute to culturing consistent microbial communities remains to be seen.

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

“…waves its chelipeds to shear off boundary layers formed by their epibionts productivity, increasing both the epibionts and, in turn, their own access to food” ( Thurber et al, 2011 ). Pointing in the same direction, a study on multiciliated surface cells in amphibian and some fish embryos ends with the hypothesis that the fluid flow generated by these cells may contribute to managing embryo-associated microbial consortia ( Kerney, 2021 ). In light of these interesting hypotheses, well-controlled perturbation experiments in Hydra may offer a unique model to study both the mechanisms and the in vivo role of host generated water flow in maintaining a stable microbiome.…”

Embryo mortality in a captive-bred, Critically Endangered amphibian

“…Vertebrate embryos were once thought to develop in a sterile, or near-sterile, environment (Escherich 1989), but with the development of culture-free, molecular-based approaches, there has been an increase in the understanding of the embryo-associated microbiome (Nyholm 2020, Kerney 2021). In addition to fun gal infection, we also isolated bacteria of the genus Herbaspirillum and Flavobacterium from 15 em bryos, including 2 healthy controls.…”