Metagenomics of the microbiome associated with the seaweed Sargassum spp. (Phaeophyceae)

Author(s)

Inara Regina Wengratt Mendonça

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2024-07-10

Examining board members

Mariana Cabral de Oliveira; Watson Arantes Gama Junior; Luiz Henrique Rosa; Nair Sumie Yokoya

• Advisor: Mariana Cabral de Oliveira

Abstract

Coastal canopies and floating masses of Sargassum are marine oases that shelter and feed a range of beings. The ecosystem services provided by this macroalgae, as well as its associated microbial community, are susceptible to environmental changes that have caused a reduction in coastal canopies and intensified the blooms of floating masses, which eventually wash up in coastal regions, causing environmental and economic impacts. Meanwhile, we are still debating the delimitation of species of the Sargassum genus on the coast of Brazil, and information about their microbiome is scarce. The microbial community associated with algae is essential in maintaining their morphology, reproduction and growth. This work aims to investigate which species of the Sargassum occurs on the Brazilian coast and describe its associated microbiome under natural and stranded conditions. To recognize the diversity and occurrence of Sargassum species, four molecular markers were used, and we identified lower genetic diversity than expected. From ten species confirmed based on morphology only two species were identified based on genetic diversity analysis. To characterize the bacterial microbiome associated with benthic and floating masses of Sargassum we used different spatial scales, including thallus structures, geographically close individuals (from a few meters to tens of km), geographically distant populations (along a latitudinal gradient in the Southwest Atlantic and in comparisons with data from other continents), morphospecies, and life habitats (benthic x holopelagic). Overall, our results indicate that: the microbiome is variable between thallus structures with the holdfast harboring the most distinct microbiome with dominance of Desulfocapsaceae, while phylloids and receptacles showcased photosynthetic cyanobacteria. The structure of the thallus creates a morphological niche that favors specific bacterial growth and some of these bacteria are common in the Sargassum genus on other continents, which opens the possibility of unveiling functional interactions in marine algae from different ecosystems. Considering the geographic scale, we found that geographically close individuals do not present significant variation in the microbiome, but when the distances are greater (around 20 km) the observed differences increase, even within the same morphospecies and habitat. The characterization of the microbiome dynamics under stranded situation was done through stranding simulations of benthic and holopelagic forms of Sargassum. The results obtained showed a process of dysbiosis in the microbiome of Sargassum within the first 24 hours of stranding. However, Vibrionales was the dominant bacterial order in the stranding simulation of holopelagic forms, while Oscillospirales, Clostridiales and Erysipelotrichales orders were predominated in the stranding simulation of benthic Sargassum cymosum. The holopelagic Sargassum stranded simulation biomass was also used to characterize the biochemical aspects of stranded Sargassum for up to 120 hours. The results showed that changes in biochemical composition during the degradation process are different between the morphotypes S. fluitans III and S. natans VIII, however, up to 120 hours of stranding there is enough lipids, proteins, carbohydrates and phenolic compounds to be extracted. The large-scale DNA sequencing and analysis of the Sargassum microbiome are unprecedented for the Brazilian coastline and significantly contribute to understanding the microbiome associated with tropical/subtropical marine macroalgae. Across all sampling sites we identified Rhodobacterales, Microtrichales and Chitinophagales as main orders dominating the bacterial microbiome. The results obtained from this work thus allowed us to establish a baseline of the diversity of bacteria associated with Sargassum on the coast of Brazil, which is relevant for future studies. (AU)

• FAPESP's process: 18/17843-4 - Metagenomics of the microbiome associated with the seaweed Sargassum spp. (Phaeophyceae)
• Grantee: Inara Regina Wengratt Mendonça
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)