Seaweeds are of significant interest in the food, pharmaceutical, and agricultural industries as they contain several commercially relevant bioactive compounds. Current extraction methods for macroalgal-derived metabolites are, however, problematic due to the complexity of the algal cell wall which hinders extraction efficiencies. The use of advanced extraction methods, such as enzyme-assisted extraction (EAE), which involve the application of commercial algal cell wall degrading enzymes to hydrolyze the cell wall carbohydrate network, are becoming more popular. Ascophyllum nodosum samples were collected from the Irish coast and incubated in artificial seawater for six weeks at three different temperatures (18 °C, 25 °C, and 30 °C) to induce decay. Microbial communities associated with the intact and decaying macroalga were examined using Illumina sequencing and culture-dependent approaches, including the novel ichip device. The bacterial populations associated with the seaweed were observed to change markedly upon decay. Over 800 bacterial isolates cultured from the macroalga were screened for the production of algal cell wall polysaccharidases and a range of species which displayed multiple hydrolytic enzyme activities were identified. Extracts from these enzyme-active bacterial isolates were then used in EAE of phenolics from Fucus vesiculosus and were shown to be more efficient than commercial enzyme preparations in their extraction efficiencies.

Stipitate kelp species such as Laminaria digitata dominate most cold-water subtidal rocky shores and form underwater forests which are among the most productive coastal systems worldwide. Laminaria also sustains rich bacterial communities which offer a variety of biotechnological applications. However, to date, in-depth studies on the diversity and uniqueness of bacterial communities associated with this macroalgal species, their ecological role and their interactions with the alga are under-represented. To address this, the epibacterial populations associated with different thallus regions (holdfast, stipe, meristem, blade) of this brown seaweed were investigated using high-throughput Illumina sequencing of the 16S rRNA genes. The results show that epibacterial communities of the brown seaweed are significantly different and specific to the thallus region, with the shared bacterial population comprising of only 1.1% of the total amplicon sequence variants. The diverse holdfast and blade tissues formed distinct clusters while the meristem and stipe regions are more closely related. The data obtained further supports the hypothesis that macroalgal bacterial communities are shaped by morphological niches and display specificity.

Macroalgae host diverse epiphytic bacterial communities with potential symbiotic roles including important roles influencing morphogenesis and growth of the host, nutrient exchange, and protection of the host from pathogens. Macroalgal cell wall structures, exudates, and intra-cellular environments possess numerous complex and valuable carbohydrates such as cellulose, hemi-cellulose, mannans, alginates, fucoidans, and laminarin. Bacterial colonizers of macroalgae are important carbon cyclers, acquiring nutrition from living macroalgae and also from decaying macroalgae. Seaweed epiphytic communities are a rich source of diverse carbohydrate-active enzymes which may have useful applications in industrial bioprocessing. With this in mind, we constructed a large insert fosmid clone library from the metagenome of Laminaria digitata (Ochrophyta) in which decay was induced. Subsequent sequencing of a fosmid clone insert revealed the presence of a gene encoding a bifunctional phosphomannomutase/phosphoglucomutase (PMM/PGM) enzyme 10L6AlgC, closely related to a protein from the halophilic marine bacterium, Cobetia sp. 10L6AlgC was subsequently heterologously expressed in Escherichia coli and biochemically characterized. The enzyme was found to possess both PMM and PGM activity, which had temperature and pH optima of 45°C and 8.0, respectively; for both activities. The PMM activity had a Km of 2.229 mM and Vmax of 29.35 mM min−1 mg−1, while the PGM activity had a Km of 0.5314 mM and a Vmax of 644.7 mM min−1 mg−1. Overall characterization of the enzyme including the above parameters as well as the influence of various divalent cations on these activities revealed that 10L6AlgC has a unique biochemical profile when compared to previously characterized PMM/PGM bifunctional enzymes. Thus 10L6AlgC may find utility in enzyme-based production of biochemicals with different potential industrial applications, in which other bacterial PMM/PGMs have previously been used such as in the production of low-calorie sweeteners in the food industry.

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.

Seaweeds are of huge interest in the food, pharmaceutical and agricultural industries due to their high nutritional content and the prevalence of useful bioactive compounds. Current extraction methods of macroalgal-derived metabolites are however problematic due to the complexity of the algal cell wall which hinders extraction efficiencies. The use of advanced extraction methods such as enzyme-assisted extraction (EAE), which involve the application of commercial algal cell wall degrading enzymes to hydrolyze the cell wall carbohydrate network, are becoming more popular as they allow the development of more efficient and eco-friendly processes. Ascophyllum nodosum samples were collected from the Irish coast and incubated in artificial seawater for six weeks at three different temperatures (18 °C, 25°C and 30 °C) to induce decay. Microbial communities associated with the intact and decaying macroalga were examined using Illumina Miseq sequencing and culture-dependent approaches, including the novel iChip device. The bacterial populations associated with the seaweed were observed to change markedly upon decay with a substantial decrease in the relative abundances of certain phyla including Planctomycetes and Verrucomicrobia observed during the decay period. Over 800 bacterial isolates cultured from the macroalga were screened for the production of algal cell wall polysaccharidases and a range of species from the phylum Bacteroidetes together with a number of Vibrio species which displayed multiple hydrolytic enzyme activities were identified. Extracts from these enzyme-active bacterial isolates were then used in EAE of phenolics from Fucus vesiculous and were shown to be equally efficient as commercial enzymes in their extraction efficiencies.