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

Axolotl ( Ambystoma mexicanum ) is a critically endangered salamander species and a model organism for regenerative and developmental biology. Despite life-long neoteny in nature and in captive-bred colonies, metamorphosis of these animals can be experimentally induced by administering Thyroid hormones (THs). However, biological consequences of this experimental procedure, such as host microbiota response and implications for regenerative capacity, remain largely unknown. Here, we systematically compared host bacterial microbiota associated with skin, stomach, gut tissues and fecal samples based on 16S rRNA gene sequences, along with limb regenerative capacity, between neotenic and metamorphic Axolotls. Our results show that distinct bacterial communities inhabit individual organs of Axolotl and undergo substantial restructuring through metamorphosis. Drastic restructuring was observed for skin microbiota, highlighted by a major transition from Firmicutes -enriched to Proteobacteria -enriched relative abundance and precipitously decreased diversity. Remarkably, shifts in microbiota was accompanied by a steep reduction in limb regenerative capacity. Fecal microbiota of neotenic and metamorphic Axolotl shared relatively higher similarity, suggesting that diet continues to shape microbiota despite fundamental transformations in the host digestive organs. The results provide novel insights into microbiological and regenerative aspects of Axolotl metamorphosis and will establish a baseline for future in-depth studies.