The skin microbiome of Xenopus laevis and the effects of husbandry conditions

Abstract

Background Historically the main source of laboratory Xenopus laevis was the environment. The increase in genetically altered animals and evolving governmental constraints around using wild-caught animals for research has led to the establishment of resource centres that supply animals and reagents worldwide, such as the European Xenopus Resource Centre. In the last decade, centres were encouraged to keep animals in a “low microbial load” or “clean” state, where embryos are surface sterilized before entering the housing system; instead of the conventional, “standard” conditions where frogs and embryos are kept without prior surface treatment. Despite Xenopus laevis having been kept in captivity for almost a century, surprisingly little is known about the frogs as a holobiont and how changing the microbiome may affect resistance to disease. This study examines how the different treatment conditions, “clean” and “standard” husbandry in recirculating housing, affects the skin microbiome of tadpoles and female adults. This is particularly important when considering the potential for poor welfare caused by a change in husbandry method as animals move from resource centres to smaller research colonies. Results We found strong evidence for developmental control of the surface microbiome on Xenopus laevis; adults had extremely similar microbial communities independent of their housing, while both tadpole and environmental microbiome communities were less resilient and showed greater diversity. Conclusions Our findings suggest that the adult Xenopus laevis microbiome is controlled and selected by the host. This indicates that the surface microbiome of adult Xenopus laevis is stable and defined independently of the environment in which it is housed, suggesting that the use of clean husbandry conditions poses little risk to the skin microbiome when transferring adult frogs to research laboratories. This will have important implications for frog health applicable to Xenopus laevis research centres throughout the world.

Manipulating the microbiome alters regenerative outcomes inXenopus laevistadpoles via lipopolysaccharide signalling

“…However, it is unclear from 16S rRNA data whether this isolate is identical to the Chryseobacterium detected on tadpoles. None of the six genera of note identified here, with the exception of Pseudomonas , was found among the top 50 genera detected on tadpoles or adults in the recent Piccini et al study (Piccinni et al 2021), which is to date the only other such report of skin microbiota in Xenopus tadpoles. Although the data suggested that tadpole skin microbiomes are shaped environmentally, a lack of parental contribution was not directly determined.…”

“…However, this is almost certainly affected by differences in stage/age and sample collection methods. Piccini et al swabbed month old tadpoles (expected stage 54-55, length 60-80 mm) that had been fed algae and were housed in aquaria(Piccinni et al 2021), whereas those in our study were maintained in petri dishes in MMR at a constant 18 °C, were approximately 6-7 days old (stage 46, 9-12 mm length) at sampling, and had never been fed. Further, Piccini’s tadpoles and frogs were routinely raised for the first week in penicillin and streptomycin, and could therefore have acquired their microbiome from tank water and food(Piccinni et al 2021).…”

“…Piccini et al swabbed month old tadpoles (expected stage 54-55, length 60-80 mm) that had been fed algae and were housed in aquaria(Piccinni et al 2021), whereas those in our study were maintained in petri dishes in MMR at a constant 18 °C, were approximately 6-7 days old (stage 46, 9-12 mm length) at sampling, and had never been fed. Further, Piccini’s tadpoles and frogs were routinely raised for the first week in penicillin and streptomycin, and could therefore have acquired their microbiome from tank water and food(Piccinni et al 2021). The comparison between our study and that of Piccini et al demonstrates that Xenopus microbiomes undoubtedly vary from one laboratory to another based on husbandry and other environmental variables.…”

“…This variation between tadpole cohorts may be partly due to host genetics, but is probably also attributable to environmental factors. While Xenopus microbiome work is in its infancy, Piccini et al (2021)(Piccinni et al 2021) found that although the adult X. laevis skin microbiome is subject to strong selective pressures from the host, tadpole microbiomes were more variable and influenced by environmental conditions. Interestingly, the microbiomes of the older, premetamorphic tadpoles in the Piccini study(Piccinni et al 2021) were also dominated by proteobacteria, although were not dominated by single genera as ours were.…”

Manipulating the microbiome alters regenerative outcomes in Xenopus laevis tadpoles via lipopolysaccharide signalling

“…While Xenopus microbiome work is in its infancy, Piccini et al 42 found that although the adult X. laevis skin microbiome is subject to strong selective pressures from the host, tadpole microbiomes were more variable and influenced by environmental conditions. Interestingly, the microbiomes of the older, premetamorphic tadpoles in the Piccini study 42 were also dominated by proteobacteria, although were not dominated by single genera as ours were. However, this is almost 54-55, length 60-80 mm) that had been fed algae and were housed in aquaria, 42 whereas those in our study were maintained in Petri dishes in MMR at a constant 18 C, were approximately 6-7 days old (stage 46, 9-12 mm length) at sampling and had never been fed.…”