Monoassociation with bacterial isolates reveals the role of colonization, community complexity and abundance on locomotor behavior in larval zebrafish

Background

Across taxa, animals with depleted intestinal microbiomes show disrupted behavioral phenotypes. Axenic (i.e., microbe-free) mice, zebrafish, and fruit flies exhibit increased locomotor behavior, or hyperactivity. The mechanism through which bacteria interact with host cells to trigger normal neurobehavioral development in larval zebrafish is not well understood. Here, we monoassociated zebrafish with either one of six different zebrafish-associated bacteria, mixtures of these host-associates, or with an environmental bacterial isolate.

Results

As predicted, the axenic cohort was hyperactive. Monoassociation with three different host-associated bacterial species, as well as with the mixtures, resulted in control-like locomotor behavior. Monoassociation with one host-associate and the environmental isolate resulted in the hyperactive phenotype characteristic of axenic larvae, while monoassociation with two other host-associated bacteria partially blocked this phenotype. Furthermore, we found an inverse relationship between the total concentration of bacteria per larvae and locomotor behavior. Lastly, in the axenic and associated cohorts, but not in the larvae with complex communities, we detected unexpected bacteria, some of which may be present as facultative predators.

Conclusions

These data support a growing body of evidence that individual species of bacteria can have different effects on host behavior, potentially related to their success at intestinal colonization. Specific to the zebrafish model, our results suggest that differences in the composition of microbes in fish facilities could affect the results of behavioral assays within pharmacological and toxicological studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42523-020-00069-x.

Detecting Reactive Oxygen Species Generation and Stem Cell Proliferation in the Drosophila Intestine

The conservation of intestinal stem cell crypt dynamics between Drosophila melanogaster and mammals allows for the genetically tractable fly model to be used for analyses of intestinal development, homeostasis, and renewal in relation to microbiota. The invertebrate fly model is advantageous for genetic research due to its anatomical and genetic simplicity and short lifespan. Accordingly, experimental resources such as large numbers of mutant and genetically modified flies have been developed. We have developed techniques to generate germ-free Drosophila, monoassociate them with candidate bacteria, and assess ensuing physiological responses within the gut tissue that include the generation of reactive oxygen species and cell proliferation.