In the context of improving food sustainability, while ensuring food safety and security, the search for innovative foods is crucial for the future. The French macroalgae sector is of interest because of the nutritional potential of this naturally available marine resource. Whole macroalgae are indeed little exploited as food source while they are nutritionally dense and contains relatively high levels of bioactive compounds with demonstrated potential health benefits. The multidisciplinary collaborative project ALGOMENU “Potential of macroalgae as a new sustainable food source” aims to assess the potential of whole macroalgae on the French market as a new safe food source contributing to a healthy diet through gut ecosystem modulation. We propose to 1) select macroalgae species of potential interest by biochemical composition characterisation of nutritional and bioactive profiles and test eco-friendly processes to reduce contaminants and increase bioactive compound biodisponibility ; 2) assess in vivo tolerance and impact of the selected macroalgae consumption on diet-nutrient handling as well as impact on digestive ecosystem and systemic metabolic repercussions (in particular metabolism of metals) in animals fed balanced diet vs high calorie diet, representative of the Western population; and 3) assess consumer’s acceptability of edible macroalgae and formulated products containing macroalgae into diet by sociologic, food testing and perception approaches. The results of the project will help to determine whether whole marine macroalgae are good candidate for food transition with nutritional and/or nutraceutical benefits.

Marine polysaccharides represent the most abundant and the most diverse marine biomass. These macromolécules are biosynthesized mainly by photosynthetic organisms (e.g. algae, micro-algae, cyanobacteria) and constitute a major main carbon source for heterotrophs organisms. Except glycoaminoglycans (e.g. heparin, chondroitin), terrestrial polysaccharides do not carry sulfate ester groups in contrast with marine polysaccharides. Thus the sulfation of polysaccharides other than glycosaminoglycans is considered as a necessary adaptation and a marker of marine origin. Marine polysaccharides are also very appreciated in industry for their physicochemical properties (e.g. agarose, carrageenans, alginates). Despite their ecological role, economical importance and their potential for applications, the extent of the structural diversity of marine polysaccharides is not known. During the last two decades, genome sequencing of marine organisms and of DNA from marine environmental samples (metagenomics) have generated a deluge of gene sequences; however, in contrast to terrestrial (meta)genomic investigations, the proportion of unknown protein families is higher in marine samples because oceans have been less studied so far. The functional interpretation of marine genomic and metagenomics data requires the prior functional characterization of genes/proteins to understand fundamental mechanisms encountered in marine environment such as organisms’ interactions, food-web, adaptation of populations to environmental change, etc. Interestingly, it was recently found that enzymes involved in the degradation of two marine polysaccharides (porphyran and cladophoran), were actually present in the human gut microbiota, suggesting that enzymes targeting other marine polysaccharides may be also found in this digestive system. The degradation of marine polysaccharides requires the concerted action of enzymes cocktails comprising complementary activities (GH: glycoside hydrolases, PL: polysaccharides lyases, sulfatases, etc). In the case of bacteria belonging to the phylum Bacteroidetes, genes involved in the polysaccharide degradation are clustered on the genome and co-regulated in “polysaccharides utilization loci” (PULs), each PUL targeting a specific glycan structure. Several PULs comprising GHs, PLs and sulfatases potentially targeting marine polysaccharides are predicted environmental Bacteroidetes and in Bacteroidetes from the human gut microbiome. However, the actual targets of these PULs are unknown in absence of experimental evidence for the function (specificity) of the encoded enzymes. We propose to systematically search and identify PUL putatively targeting marine polysaccharides in hundreds of genomes from sequence databanks as was already done for the PULs from 70 Bacteroidetes genomes from the human gut microbiota (www.cazy.org/PULDB). We will then select from marine and human gut Bacteroidetes about 50 PULs putatively targeting marine polysaccharides and which will represent approx. 500 genes encoding GHs, PLs, sulfatases, as well as proteins with unknown functions. All the proteins will be expressed recombinantly and will be biochemically characterized. At the end of the project we expect to have attributed the function to several marine PULs found in both marine organisms and in human gut microbiota. The results will directly impact the interpretation of marine genomic data and our understanding of the extent of the digestive abilities of the human gut microbiota.

Today, the World faces the major challenge of switching to a bioeconomy based on sustainable uses of biomass for producing chemicals and energy services. Considering biofuels for example, current industrial routes for large-scale production of bioethanol rely on sugarcane and starch plants (first-generation). Cellulosic ethanol obtained from non-food resources such as wood and straw (second-generation) is on the verge of deployment. Due to competition of uses, these processes based on terrestrial feedstock are doomed to be capped and need complementary solutions. Within this context, marine macroalgae receive increasing attention as an alternative renewable resource for producing materials, chemicals, fuels and energy with no or limited use of arable land, freshwater, fertilizers or phytosanitary products. In 2010, the world macroalgae production reached 19.9 million metric tons dry weight, 95% of which from aquaculture, with an average annual increase of 7% / year over the years 2001-2010. Brown and red seaweeds are already widely used as feedstock for biorefinery processes, mainly in the phycocolloid industry. Green macroalgae are fast growing organisms (growth rate = +10 to +30% per day), distributed worldwide. They are still under-exploited and represent a promising vector to convert solar energy and CO2 into biofuels and bioproducts at a large scale. Algae are a unique and very diverse group of organisms. Being the closest parents to terrestrial plants, green macroalgae exhibit several similarities with current 1st and 2nd generation feedstock. They are natural producers of starch and unlignified cellulose. As such, they could prove very relevant as raw materials for existing sugar transformation processes. Beside simple glucans, green macroalgae are also composed of specific sulphated polysaccharides built on uncommon neutral sugars and uronic acids, which open the way to high-value biobased intermediates for the chemical industry. Starting from those considerations, the aim of our industrial research project is to evaluate the potential of green macro-algae, from biomass cultivation to end-products, as sustainable feedstock for the production of ethanol through glucose fermentation. Our first targets are to develop efficient biomass production schemes and optimized enzymatic hydrolysis of seaweed glucans to produce algal glucose. In a second step, glucose can lead to many platform molecules. As proof of concept, we will focus on fermentation into ethanol. In a biorefinery concept, other specific green seaweed carbohydrates and non-carbohydrate components will be investigated, in order to identify and quantify potential interesting compounds. To reach these objectives, our proposal brings together a comprehensive consortium with key competencies in seaweed cultivation, biomass fractionation, polysaccharides, biochemistry, biofuels, technico-economic and life-cycle assessments.