Plastic Debris as Ecological Drivers of Green Turtle Microbiome and Their Connectivity with Antibiotic Resistance Genes

Plastic pollution in oceans poses a major threat to marine life, not only through ingestion and entanglement but also by serving as a surface for microbial colonization, harboring potential pathogens and antibiotic resistance genes (ARGs). Sea turtles, particularly green turtles (Chelonia mydas), are highly susceptible to plastic ingestion, making them suitable sentinels for assessing plastisphere impacts. This study investigated whether plastic-associated microbiota influence the microbiome of green turtles and act as vectors for pathogenic bacteria and ARGs. Samples from turtles, along with seawater, two species of algae, and plastic samples, were collected at Itaipu Beach, Rio de Janeiro, Brazil. DNA was extracted and analyzed using high-throughput 16S rRNA gene sequencing and high-throughput quantitative PCR targeting ARGs and bacterial abundances. Contrary to expectations, the turtle microbiome exhibited greater similarity to plastic-associated microbial assemblages than to those from algae (their primary dietary resource) or seawater (the surrounding environment). Pathogenic genera, including Vibrio, Pseudomonas, Bacillus, Staphylococcus, and Clostridium, were shared between plastics and turtles. Although a high number and abundance of ARGs were detected in both matrices, their profiles suggested limited selection or transfer relative to pathogenic taxa, indicating that potential pathogens may be more effectively transmitted from plastics to hosts than resistance determinants. Overall, plastic debris functions as a microbial vector reshaping host-associated communities more strongly than natural diet or seawater, with a limited influence on antibiotic resistance genes. Rather than merely harboring microbes, plastics appear capable of transmitting opportunistic pathogens to marine hosts, underscoring their emerging ecological and health risks.