Metagenomic analysis reveals significant seasonal variations in the epiphytic bacterial communities associated with different parts of the brown seaweed Laminaria digitata

Brown seaweeds such as Laminaria species are a rich source of polysaccharides such as laminarin and fucoidan which have a variety of functional food and animal feed applications, as well as alginates with demonstrated biological and pharmacological activities. Macroalgal surfaces are rich in carbon-based constituents which provide a suitable environment for growth and colonization by diverse bacterial communities. Several environmental and non-environmental factors can influence the composition and abundance of epibacterial communities associated with seaweeds. In addition to the biological, physical and chemical properties of the macroalgal surface, seasonal variations have been found to play a significant role in the structure of the associated microbial communities. Variations in macroalgal epibacterial communities have also been observed within different parts of the host algal species. However, to date, in-depth studies on bacterial communities associated with macroalgal species, their ecological role and interactions with the algae are still scarce. To gain an insight into the diversity and composition of the microbial communities associated with the brown alga Laminaria digitata, the communities derived from different parts of the alga including the blade, meristem, stipe and holdfast; were investigated using metagenomic Illumina sequencing of 16S rRNA gene amplicons. Seasonal variations in the microbial populations were found in samples taken from the Irish coast in different seasons between 2017 and 2018. This metagenomic-based investigation provides a detailed view of the seasonal variations in the bacterial populations associated with Laminaria digitata and helps provide further insights into potential interaction between this macroalga and its epiphytic bacterial communities.