Use of Deep Sequencing to Evaluate Transitions in Microbial Communities in Stranded Sargassum.

Deep sequencing technologies can be used to evaluate pathogens in environmental samples. The objective of this study was to use this technology to evaluate Sargassum samples that were characterized by different stranding times, one classified as short-term stranded (STS) and another classified as long-term stranded (LTS) Sargassum. Nine replicates of the STS Sargassum showed a range in Shannon diversity between 3.04 and 3.38, whereas 11 replicates of LTS showed a range between 1.17 and 1.22. Nonmetric multidimensional scaling analysis showed distinct differences between STS and LTS by about 0.5 coordinate units, while variations within replicates ranged by 0.1 coordinate units. Comparison between the two Sargassum samples showed a greater abundance of Vibrio species in STS Sargassum when compared to LTS Sargassum, with major pathogenic forms observed for Vibrio alginolyticus (11%), Vibrio parahaemolyticus (1.5%), and Vibrio vulnificus (0.29%). Additional known human pathogens were observed, including Listeria monocytogenes, Legionella pneumophila, and Staphylococcus aureus, as well as the presence of gut commensals and fecal coliforms. Overall results show that deep sequencing analysis of these environmental samples was reproducible. Given the abundance of pathogenic bacteria, more research is needed to evaluate the risk of disease transmission as Sargassum strands and decomposes on coastal beaches.