The red alga Asparagopsis armata is a species with a haplodiplophasic life cycle alternating between morphologically distinct stages. The species is known for its various biological activities linked to the production of halogenated compounds, which are described as having several roles for the algae such as the control of epiphytic bacterial communities. Several studies have reported differences in targeted halogenated compounds (using gas chromatography–mass spectrometry analysis (GC-MS)) and antibacterial activities between the tetrasporophyte and the gametophyte stages. To enlarge this picture, we analysed the metabolome (using liquid chromatography–mass spectrometry (LC-MS)), the antibacterial activity and the bacterial communities associated with several stages of the life cycle of A. armata: gametophytes, tetrasporophytes and female gametophytes with developed cystocarps. Our results revealed that the relative abundance of several halogenated molecules including dibromoacetic acid and some more halogenated molecules fluctuated depending on the different stages of the algae. The antibacterial activity of the tetrasporophyte extract was significantly higher than that of the extracts of the other two stages. Several highly halogenated compounds, which discriminate algal stages, were identified as candidate molecules responsible for the observed variation in antibacterial activity. The tetrasporophyte also harboured a significantly higher specific bacterial diversity, which is associated with a different bacterial community composition than the other two stages. This study provides elements that could help in understanding the processes that take place throughout the life cycle of A. armata with different potential energy investments between the development of reproductive elements, the production of halogenated molecules and the dynamics of bacterial communities.

The increasing use of chemicals requires a better understanding of their presence and dynamics in the environment, as well as their impact on ecosystems. The aim of this study was to validate the first steps of an innovative multi-omics approach based on metabolomics and 16S metabarcoding data for analyses of the fate and impact of contaminants in Mediterranean lagoons. Semi-targeted analytical procedures for water and sediment matrices were implemented to assess chemical contamination of the lagoon: forty-six compounds were detected, 28 of which could be quantified in water (between 0.09 and 47.4 ng/L) and sediment (between 0.008 and 26.3 ng/g) samples using the UHPLC-MS/MS instrument. In addition, a non-targeted approach (UHPLC-HRMS) using four different sample preparation protocols based on solid/liquid extractions or an automated pressurized fluid extraction system (EDGE^®) was carried out to determine the protocol with the best metabolome coverage, efficiency and reproducibility. Solid/liquid extraction using the solvent mixture acetonitrile/methanol (50/50) was evaluated as the best protocol. Microbial diversity in lagoon sediment was also measured after DNA extraction using five commercial extraction kits. Our study showed that the DNeasy PowerSoil Pro Qiagen kit (Promega, USA) was the most suitable for assessing microbial diversity in fresh sediment.

The increasing use of chemicals requires a better understanding of their presence and their dynamics in the environment as well as their impact on ecosystems; it is therefore important to set up procedures. The aim of this study was to validate the first steps of an innovative multi-omics approach based on metabolomics and 16S metabarcoding data for future analyses of the contaminants fate and impact in Mediterranean lagoons. First, semi targeted analytical procedures for water and sediment matrices were set up to evaluate the lagoon contamination status. Forty-six compounds were detected, 28 could be quantified in both water (between 0.09 and 47.4 ng/L) and sediment (between 0.008 and 26.3 ng/g) samples using UHPLC-MS/MS instrument. Regarding the non-targeted metabolomics study (UHPLC-HRMS), four sample preparation protocols, based on solid/liquid extractions and an automated pressurized fluid extraction system (EDGE® extractions), were compared in terms of metabolome coverage, efficiency and reproducibility of the extraction methodology. A solid/liquid extraction using acetonitrile/methanol (50/50) solvent was the best protocol. On the other hand, in order to characterize the microbial diversity of the lagoon sediment using metabarcoding, five commercial kits for DNA extraction were evaluated. This study revealed that the DNeasy PowerSoil Pro Qiagen Kit (Promega, USA) was the best compromise for studies assessing microbial diversity in fresh sediment.