S2 Data -

Sargassum spp. flood the Caribbean coastline, causing damage to the local economy and environment. Anaerobic digestion (AD) has been proposed as an attractive option for turning macroalgae into valuable resources. Sargassum spp. has a complex composition that affects the microbial composition involved in AD which generates a low methane yield. This study aimed to improve the methane yield of pelagic Sargassum, using different energy-saving pretreatments and identifying the microbial community associated with methane production. We applied different energy-saving pretreatments to algal biomass and assessed the methane yield using a biomethane potential (BMP) test. The microbial communities involved in the AD of the best- and worst-performing methanogenic systems were analyzed by high-throughput sequencing. The results showed that pretreatment modified the content of inorganic compounds, fibers, and the C:N ratio, which had a strong positive correlation with BMP. The water washing pretreatment resulted in the best methane yield, with an increase of 38%. DNA metabarcoding analysis revealed that the bacterial genera Marinilabiliaceae_uncultured, DMER64, Treponema, and Hydrogenispora, as well as the archaea genera Methanosarcina, RumEn_M2, Bathyarchaeia, and Methanomassiliicocus, dominated the microbial community with a high methane yield. This study is the first to demonstrate the microbial community structure involved in the AD of Sargassum spp. The pretreatments presented in this study can help overcome the limitations associated with methane yield.