Characterisation of the gut microbiome and surveillance of antibiotic resistance genes in green sea turtles (Chelonia mydas).

Green sea turtles (Chelonia mydas) are globally endangered marine herbivores that maintain the health of seagrass and coastal ecosystems. Their populations are declining due to human activities, including environmental pollution, which can disrupt gut microbial communities and compromise nutrition, immunity, and overall health. In this study, cloacal swabs from 139 green sea turtles categorised as captive juveniles, captive adults and wild stranded animals in the Gulf of Thailand, were analysed via shotgun metagenomic sequencing to elucidate bacterial taxonomic diversity and ARG profiles. In captive juveniles, Pseudomonadota was the most abundant phylum, followed by Ascomycota and Basidiomycota. In captive adults, Pseudomonadota exhibited an even greater predominance, with only minor contributions from unclassified bacteria and other taxa. In wild stranded green sea turtles, Pseudomonadota was dominant in their gut microbiome, but this was accompanied by notable levels of Actinomycetota, Bacteroidota, and Bacillota. Stranded turtles exhibited highest microbial diversity and variability, while captive adult turtles showed the lowest. Resistome profiling also revealed significant differences in the relative abundance of antibiotic resistance genes across all three groups. MacB (macrolide resistance) was the most abundant gene overall, with the highest abundance observed in juveniles (4.8 %). Stranded turtles exhibited elevated levels of TetA(58) (tetracycline resistance, 2.6 %) and msbA (nitroimidazole resistance, 2.2 %), while adults showed the greatest enrichment of Ecol_fabG_TRC (triclosan resistance, 3.8 %) and TxR (tetracycline resistance, 3.6 %). These data demonstrate that marked variability existed in the gut microbiome and resistome of green sea turtles across different life stages in captive or wild environments. This offers critical insights for the development of targeted conservation strategies and health management practices for both wild and captive green sea turtles. Strategies to mitigate the spread of antibiotic resistance should be developed.