Enrique Salgado-Hernández

In recent years, pelagic Sargassum has invaded the Caribbean coasts, and anaerobic digestion has been proposed as a sustainable management option. However, the complex composition of these macroalgae acts as a barrier to microbial degradation, thereby limiting methane production. Microbial adaptation is a promising strategy to improve substrate utilization and stress tolerance. This study aimed to investigate the adaptation of a microbial consortium to enhance methane production from the pelagic Sargassum. Microbial adaptation was performed in a fed-batch mode for 100 days by progressive feeding of Sargassum. The evolution of the microbial community was analyzed by high-throughput sequencing of 16S rRNA amplicons. Additionally, 16S rRNA data were used to predict functional profiles using the iVikodak platform. The results showed that, after adaptation, the consortium was dominated by the bacterial phyla Bacteroidota, Firmicutes, and Atribacterota, as well as methanogens of the families Methanotrichaceae and Methanoregulaceae. The abundance of predicted genes related to different metabolic functions was affected during the adaptation stage when Sargassum concentration was increased. At the end of the adaptation stage, the abundance of the predicted genes increased again. The adapted microbial consortium demonstrated a 60% increase in both biomethane potential and biodegradability index. This work offers valuable insights into the development of treatment technologies and the effective management of pelagic Sargassum in coastal regions, emphasizing the importance of microbial adaptation in this context.

In recent years, pelagic Sargassum has invaded the Caribbean coasts, and anaerobic digestion has been proposed as a sustainable management option. However, the complex composition of these macroalgae acts as a barrier to microbial degradation, thereby limiting methane production. Microbial adaptation has emerged as a promising strategy to improve substrate utilization and stress tolerance. This study aimed to investigate the adaptation of a microbial consortium to enhance methane production from the pelagic Sargassum. Microbial adaptation was carried out for 100 days by progressively feeding Sargassum. The evolution of the microbial community was analyzed by high-throughput sequencing of 16S rRNA amplicons. Additionally, 16S rRNA data were used to predict functional profiles using the iVikodak platform. The results showed that, after adaptation, the consortium was dominated by the bacterial phyla Bacteroidota, Firmicutes, and Atribacterota, as well as methanogens of the families Methanotrichaceae and Methanoregulaceae. The abundance of genes related to different metabolism-related functions decreased on day 60 when the Sargassum concentration increased. However, after 100 d, the functions increased again, enhancing methane production. The adapted consortium (AC) exhibited a biomethane potential of 160.03 ± 4.64 N-mL g^− 1 VS and a biodegradability index of 39%, representing a 60% improvement. Additionally, the degradation kinetics and methane production of pelagic Sargassum were improved. The study concludes that microbial adaptation enhances the bioconversion of pelagic Sargassum into methane. It is also suggested that a microbial consortium should be generated to achieve greater efficiency in the bioconversion of Sargassum, along with other pretreatments.

In the past decade, Sargassum natans and S. fluitans have massively reached the Mexican Caribbean shores. As a result, Sargassum confinement sites may be affecting the soil quality and health in coastal ecosystems and agroecosystems. The impact of Sargassum (e.g., polyphenols) on soil biodiversity has not yet been evaluated. Terrestrial ecotoxicological tests use the epigean earthworm Eisenia fetida as a model organism to assess the function of soil habitats. This study evaluated the behavior and survival of the earthworm E. fetida exposed to five Sargassum concentrations (0, 25, 50, 75, and 100 %) using two toxicological tests. The avoidance test showed that E. fetida repelled (>80 %) a diet with 100 % Sargassum . In contrast, the acute test recorded a low mortality; however, the growth of E. fetida was lower with increasing Sargassum concentrations. It is concluded that the ability to repel and E. fetida biomass are early warning bioindicators to predict the environmental risk of Sargassum in soil. Therefore, it is relevant to determine the potential risk of using earthworm compost and Sargassum leachates as biofertilizers in agroecosystems.

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.

Sargassum spp. floods the Caribbean coastlines, causing damage to the local economy and environment. These macroalgae have a low methane yield that makes the anaerobic digestion (AD) process unviable, so low-cost pretreatments are required. This research investigated the efficiency of energy-saving pretreatments, such as water washing, that had not been evaluated for these species. The microbial communities involved in AD of the best and worst-performing systems were also analyzed by high-throughput sequencing. The results showed that water washing pretreatment modified the content of inorganic compounds, fibers, and C:N ratio and increased the methane yield by 38%. The bacterial phyla Bacteroidota, Firmicutes, and Thermotogota, as well as the archaea genera Methanosarcina , RumEn_M2 , and Bathyarchaeia , dominated the microbial communities. This study is the first to show the microbial community structure involved in the AD of Sargassum spp. The pretreatments presented in this study may help overcome the previously reported limitations.

In the last decade, Sargassum spp. seaweed species have caused massive flooding on the Caribbean Sea coasts. These seaweed species have a high content of recalcitrant compounds, such as insoluble fibers and polyphenols, which generate low methane yields in anaerobic digestion (AD). This study investigated the effect of solid–liquid separation of Sargassum biomass on biodegradability and methane yield. A biochemical methane potential (BMP) test was conducted with both fractions and raw biomass (RB). A mass balance was developed to assess the distribution of the components. The obtained liquid fraction (LF) showed high biodegradability and a high methane production rate, and it generated a methane yield of 159.7 ± 7.1 N L kg VS⁻¹, a value that corresponds to approximately twice that achieved with RB and the solid fraction (SF). The component distribution analysis showed that about 90% of total solids (TS), volatile solids (VS), ash, carbon, and cellulose were retained in the SF. In conclusion, the LF had high biodegradability and methane yield. This suggests the potential for LFs of Sargassum biomass to be treated in large-scale high-load reactors; however, studies applied to SFs are needed because they retain a large amount of organic matter with low biodegradability.