Experimentally Induced Metamorphosis in Axolotl (Ambystoma mexicanum) Under Constant Diet Restructures Microbiota Accompanied by Reduced Limb Regenerative Capacity

Abstract

38Axolotl (Ambystoma mexicanum) is a critically endangered salamander species and a 39 model organism for regenerative and developmental biology. Despite life-long neoteny in 40 nature and in captive-bred colonies, metamorphosis of these animals can be 41 experimentally induced by administering Thyroid hormones (THs). However, biological 42 consequences of this experimental procedure, such as host microbiota response and 43 implications for regenerative capacity, remain largely unknown. Here, we systematically 44 compared host bacterial microbiota associated with skin, stomach, gut tissues and fecal 45 samples based on 16S rRNA gene sequences, along with limb regenerative capacity, 46 between neotenic and metamorphic Axolotls. Our results show that distinct bacterial 47 communities inhabit individual organs of Axolotl and undergo substantial restructuring 48 through metamorphosis. Drastic restructuring was observed for skin microbiota, 49 highlighted by a major transition from Firmicutes-enriched to Proteobacteria-enriched 50 relative abundance and precipitously decreased diversity. Remarkably, shifts in 51 microbiota was accompanied by a steep reduction in limb regenerative capacity. Fecal 52 microbiota of neotenic and metamorphic Axolotl shared relatively higher similarity, 53suggesting that diet continues to shape microbiota despite fundamental transformations in 54 the host digestive organs. The results provide novel insights into microbiological and 55 regenerative aspects of Axolotl metamorphosis and will establish a baseline for future in-56 depth studies. 57 58 59 60 61 62 63 Metazoan genomes have diversified and evolved in the presence of associated host 64 microbiota. The evolution of morphology and function of animal organ systems may have 65 been influenced by interactions with their microbial partners 1 . From the host perspective, 66 symbioses between metazoans and microbes provide a synergetic impact to operate 67 essential functions for normal growth, development and behavior 2-4 . Studies on host-68 microbiome interactions in health and disease conditions indicate that perturbation of the 69 crosstalk between the host and microorganisms may lead to deleterious consequences 70 such as developmental defects 3,5 , increased susceptibility to infectious diseases 6,7 and 71 ultimately fitness costs 8 . Even though host genotypes 9 and environmental factors, such 72 as diet and habitat 10,11 , were shown to strongly impact the composition and structure of 73 animal microbiota, ecological forces shaping assembly of the host associated microbial 74 communities have still been poorly understood. 75 76 Amphibians, which undergo dramatic morphological changes through metamorphosis, 77 exhibit explicitly altered biphasic life stages to tackle developmental challenges. 78 Remarkably, metamorphosis in several marine animal species such as sponges, corals, 79 crabs, sea urchins, an ascidians is mediated by bacterial community 12 . Thyroid hormones 80 (THs) are key players in initiation and completion of metamor...

A comparison of nonlethal sampling methods for amphibian gut microbiome analyses

“…Similar to other studies of the gut microbiome across taxa, we found that both sex and body weight were important factors accounting for interindividual variation in community assemblage. However, further work is needed to identify the effect of metamorphic transition in cane toad gut microbiomes given that previous studies have shown that this is a factor regulating the composition of the microbiome in amphibians (Demircan et al, ).…”