Comparative analysis of microbial diversity and pathogenic potential in marine litter reveals timber as a key reservoir in sandy beaches ecosystems

Many materials create new habitats for microbial colonization and the persistence of potentially pathogenic bacteria. Despite this, comparative studies addressing the microbial diversity and pathogenic potential across different types of marine litter remain scarce. This study investigated microbial communities associated with plastics, aluminum, and timber collected from the strandline of two types of beaches. Amplicon sequencing of the 16S rRNA gene revealed that bacterial community structure and diversity varied primarily according to substrate type rather than beach environment. Nevertheless, all types of marine litter evaluated hosted rich and diverse bacterial communities, with several taxa recognized as potential pathogens of both marine organisms and humans. Timber supported the richest, most diverse, and most specific microbiome, including a high number of taxa known to contain potential pathogens. Among these, Flavobacterium, Mycobacterium, Pseudoalteromonas, Acinetobacter, and Staphylococcus were particularly notable, as they are recognized pathogens of both marine organisms and humans, representing potential ecological and sanitary risks. These findings highlight that marine litter on sandy beaches functions as a selective substrate influencing biofilm formation, microbial dispersal, and the persistence of pathogens in coastal ecosystems. Timber, in particular, emerges as an underrecognized reservoir for microbial diversity and resistance genes, warranting greater attention in marine pollution and public health monitoring.