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Worldwide, novel species of pathogens are frequently reported in cultivated and wild macroalgae. Alongside the rapid growth of the seaweed industry, diseases and pests have become an area of significant concern for cultivation and conservation of wild stocks alike: yield and quality of a crop might be greatly affected and sometimes, the losses due to diseases and pests are such that they jeopardize the economic viability of cultivation. Disease management methods and biosecurity are still in their infancy, especially as disease-causing organisms are most often poorly known, with limited options for robust and rapid diagnostics. Here, we describe a community-based, multilingual initiative that aims to foster the description of disease-causing organisms relevant to the seaweed industry worldwide and to underpin the conservation of wild seaweed genetic resources.

The sugar kelp Saccharina latissima dominates many temperate coastal ecosystems, plays key ecological roles and presents important economic potential. However, its microbiota remains poorly investigated, although it could play an important role in algal fitness. In this study, we combined high throughput Illumina-based DNA sequencing and Fluorescence In Situ Hybridization to perform a culture-independent investigation of the S. latissima bacterial and fungal microbiota. Up to 600 bacterial and 100 fungal Amplicon Sequence Variants were identified per algal individual, revealing diverse bacterial and fungal communities associated to S. latissima. Overall, bacterial communities were dominated by Proteobacteria, Actinobacteria, and Bacteroidetes, in particular Hyphomonadaceae and Cyclobacteriaceae. Fungal communities were dominated by Ascomycota and Basidiomycota, in particular Mycosphaerellaceae, Psathyrellaceae, and Bulleribasidiaceae. Our results also revealed a variable distribution of S. latissima microbiota, as two adjacent tissue samples typically contained distinct fungal and bacterial assemblages, and CARD-FISH analysis detected microbial endosymbionts (with a few epibionts). Complementary analyses showed that despite achieving a good sequencing coverage for each tissue sample, the unexpected diversity and variability of ASVs made the definition of a core fungal and bacterial microbiota difficult, and highlights novel avenues to overcome the limitations of current surface-sterilization and metabarcoding protocols.

The eucheumatoids Kappaphycus and Eucheuma are cultivated in tropical or subtropical regions for the production of carrageenan, a hydrocolloid widely used in the food and cosmetic industries. Kappaphycus alvarezii is a highly valued economic crop in the Coral Triangle, with the Philippines, Indonesia and Malaysia ranked among the largest producers. In the absence of measures to mitigate climate change, extreme events including heatwaves, typhoons, severe El Niño and La Niña, are expected to increase in frequency and magnitude. This inadvertently brings adverse effects to the seaweed cultivation industry, especially in the tropics. Temperatures are rapidly reaching the upper limit of biologically tolerable levels and an increase in reports of ice-ice and pest outbreaks is attributable to these shifts of environmental parameters. Nevertheless, few reports on the response of eucheumatoids to a changing environment, in particular global warming, are available. Understanding the responses and possible mechanisms for acclimation to warming is crucial for a sustainable seaweed cultivation industry. Here, the physiological and biochemical responses of K. alvarezii to acute warming indicated that the strain used in the current study is unlikely to survive sudden increases in temperature above 36°C. As temperature increased, the growth rates, photosynthetic performance, phycocolloid quality (carrageenan yield, gel strength and gel viscosity) and pigment content (chlorophyll-a, carotenoid and phycobiliproteins) were reduced while the production of reactive oxygen species increased indicating the occurrence of stress in the seaweeds. This study provides a basis for future work on long term acclimation to elevated temperature and mesocosm-based multivariate studies to identify heat-tolerant strains for sustainable cultivation.

The aquaculture of macroalgae for human consumption and other high-end applications is experiencing unprecedented development in European countries, with the brown algae Saccharina latissima being the flag species. However, environmental conditions in open sea culture sites are often unique, which may impact the biochemical composition of cultured macroalgae. The present study compared the elemental compositions (CHNS), fatty acid profiles, and lipidomes of S. latissima originating from three distinct locations (France, Norway, and the United Kingdom). Significant differences were found in the elemental composition, with Norwegian samples displaying twice the lipid content of the others, and significantly less protein (2.6%, while French and UK samples contained 6.3% and 9.1%, respectively). The fatty acid profiles also differed considerably, with UK samples displaying a lower content of n-3 fatty acids (21.6%), resulting in a higher n-6/n-3 ratio. Regarding the lipidomic profile, samples from France were enriched in lyso lipids, while those from Norway displayed a particular signature of phosphatidylglycerol, phosphatidylinositol, and phosphatidylcholine. Samples from the UK featured higher levels of phosphatidylethanolamine and, in general, a lower content of galactolipids. These differences highlight the influence of site-specific environmental conditions in the shaping of macroalgae biochemical phenotypes and nutritional value. It is also important to highlight that differences recorded in the lipidome of S. latissima make it possible to pinpoint specific lipid species that are likely to represent origin biomarkers. This finding is relevant for future applications in the field of geographic origin traceability and food control.

Nicotiana tabacum Togt encodes a scopoletin glucosyltransferase (UDPglucose:scopoletin O-β-D-glucosyltransferase, EC 2.4.1.128) known to act in vitro on many different substrates including the 6-methoxy-7-hydroxy- coumarin scopoletin. This phenolic compound accumulates in vast amounts, essentially in its glucosylated form scopolin, in tobacco during the hypersensitive response (HR) to tobacco mosaic virus (TMV). To identify the physiological role of this pathogen-inducible UDP-Glc glucosyltransferase (UGT), we generated TOGT over-expressing transgenic plants. Although no endogenous scopoletin or scopolin could be detected before infection, the accumulation of both the aglycone and the glucoside was found to be 2-fold higher in transgenic plants after inoculation with TMV than in wild-type plants. Scopoletin UGT activity in plants over-expressing Togt was significantly higher during the HR than in control plants. This up-regulated activity was associated with a strong increase of the bright blue fluorescence surrounding the HR-necrotic lesions under UV light, which is known to correlate with scopoletin and scopolin abundance. Necrosis appeared sooner in transgenic plants and lesions developed faster, suggesting an accelerated HR. Unexpectedly, the viral content in each lesion was not significantly different in transgenic and in wild-type plants. These results are discussed in relation to the role of TOGT as the major UDP-Glc: scopoletin glucosyltransferase and to the importance of scopoletin accumulation during the HR. [ABSTRACT FROM AUTHOR]