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

Abstract

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.

Transplantation of high fat fed mouse microbiota into zebrafish larvae identifies MyD88‐dependent acceleration of hyperlipidaemia by Gram‐positive cell wall components

“…Most zebrafish embryo mono-association studies have been carried out with Gram-negative organisms including E. coli, A. veronii, V. cholerae, and P. aeruginosa. [18][19][20] The comparison of heat killed E. faecalis to heat killed S. xylosus demonstrated an increased ability of heat killed E. faecalis to accelerate diet-induced hyperlipidaemia. This suggests that there is variability in hyperlipidaemia accelerating potential amongst Gram-positive organisms in zebrafish embryos.…”

“…The presence of this response in zebrafish embryos has broad implications for the use of zebrafish embryos to study transplanted mammalian microbiota as it may not be representative of the mammalian response to colonization with Gram‐positive organisms. Most zebrafish embryo mono‐association studies have been carried out with Gram‐negative organisms including E. coli , A. veronii , V. cholerae , and P. aeruginosa 18–20 …”

Larval Zebrafish as a Model for Mechanistic Discovery in Mental Health

“…Germ-free (GF) zebrafish exhibited increased locomotor activity and reduced thigmotactic behavior compared to conventionalized (CV) and conventionally-raised (CR) larvae (Davis et al, 2016;Weitekamp et al, 2021). Furthermore, bacterial load was found to be inversely related to locomotor activity (Weitekamp et al, 2021). However, Phelps et al (2017) reported no difference in thigmotaxis regardless of colonization, despite GF larvae displaying hyperactivity in dark periods by 10 dpf.…”

“…The microbial status of larvae also influences their anxiety or mood-related behavior. Germ-free (GF) zebrafish exhibited increased locomotor activity and reduced thigmotactic behavior compared to conventionalized (CV) and conventionally-raised (CR) larvae (Davis et al, 2016;Weitekamp et al, 2021). Furthermore, bacterial load was found to be inversely related to locomotor activity (Weitekamp et al, 2021).…”

Application of zebrafish in the study of the gut microbiome

“…Manipulating the gut microbiome composition in zebrafish may also affect the nervous system. By co‐culturing GF zebrafish with six selected bacteria, either single strain or mixed strains, Weitekamp et al showed that different bacterial species had different effects on their host's behavior, which might be correlated with colonization success in the host's intestine 29 . Borrelli et al found variations in the gut microbial composition in the probiotic Lactobacillus rhamnosus treatment group, with a significant increase in Firmicutes and decrease in Proteobacteria, including potential pathogens (such as Plesiomonas and Vibrio ).…”