First insights into the Drivers of the Cloacal Microbiome of the Wild Platypus (Ornithorhynchus anatinus).

The host microbiome plays a critical role in wildlife health, reproduction, and environmental responses. The platypus (Ornithorhynchus anatinus), a semi-aquatic monotreme endemic to eastern Australia, has remained microbiologically understudied despite conservation concern. Here, we present the first characterisation of the wild platypus cloacal microbiome using 16 S rRNA amplicon sequencing of samples collected across its eastern range, including sites recently affected by drought and bushfire. We found that region, and environmental disturbances such as bushfire and drought were significant drivers of bacterial community structure and composition, with influence from sex and breeding season also. Bushfire and drought both disrupted microbial community structure. The microbiome partially recovered following low-severity fires, but not after severe fire or prolonged drought, suggesting that microbiome resilience is linked to disturbance intensity. These findings suggest that the platypus microbiome is sensitive to environmental pressures and may offer a minimally invasive indicator of individual and ecosystem health. In addition to these ecologically important findings, across all sampled regions the platypus cloacal microbiome was consistently dominated by Campylobacterota and Fusobacteriota, with Pseudomonadota and Bacillota also prominent in the core microbiomes. Our results provide a critical baseline for integrating microbial health into conservation planning for this unique mammal.