"Let's Dry up and Survive Together": Is Anhydrobiosis in Two Paramacrobiotus Species (Tardigrada) Associated with a Specific Microbiome Community?

This study reports, for the first time, changes in the microbiome community associated with anhydrobiosis in two tardigrade species of the genus Paramacrobiotus. To identify bacteria linked to the anhydrobiosis phenomenon and to track microbiome changes under anhydrobiotic stress, next-generation sequencing of bacterial 16S rRNA genes was conducted. Microbiome profiling was performed across various developmental and physiological stages of tardigrades, including: eggs; active adult specimens (both before and after 7, and 120 days of anhydrobiosis, referred to as short- and long-term anhydrobiosis, respectively); specimens in the desiccated tun stage; dead specimens following long-term anhydrobiosis (no dead specimens were observed after short-term anhydrobiosis); and the culture medium. It was shown that the microbiome community varied among stages, with high stage-specificity. Several bacterial genera were identified that may assist the host during anhydrobiosis, potentially through biofilm formation and by supporting stress-protective mechanisms such as heat shock protein expression and trehalose synthesis in eggs and tuns. These findings reveal that microbiota may contribute to anhydrobiotic survival in tardigrades, providing novel insights into host-microbe interactions under extreme environmental stress.