Discovery of novel enzymes for the valorization of algal biomass – BLUE ENZYMES

To discover novel enzymes specific for algal polysaccharides, we are using a multidisciplinary strategy combining catabolic and transcriptomic profiling, comparative genomics and reconstruction of metabolic networks. The most promising candidate enzymes from marine flavobacteria will be overexpressed in Escherichia coli using a medium throughput approach. After an activity screening step using algal polysaccharides and oligosacccharides, the novel active enzymes will be studied in depth at both the biochemical and structural level.

Model marine flavobacteria (e.g. Zobellia galactanivorans, Tenacibacullum maritimum) were analyzed at the genomic and transcriptomic level, focusing on their capacities to use marine polysaccharides. Based on these analyses, 192 candidate-enzymes were selected and overexpressed (61% soluble). Several new polysaccharidases were biochemically and structurally characterized (e.g. beta-glucanase, atypical beta-agarase, chondroitinase B). A particularly emblematic result was the discovery and the integrative characterization of the complete catabolic pathway for carrageenans in marine bacteria.

Numerous functional genomic and biochemical studies have been initiated within the Blue Enzymes project and will be finalized beyond the official end of the project. New polysaccharidases have been patented and will be exploited, notably in the context of the creation in Roscoff of the scientific park « Blue Valley Park » which is dedicated to marine biotechnology. Finally, the Blue Enzymes project has contributed to the organization of the 1st international congress on marine flavobacteria (Cargèse, June 2018). The next edition of this congress will take place in 2021 in Roscoff.

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Patent
Ficko-Blean E, Larocque R, Correc G, Czjzek M, Michel G. Alpha-1,3-(3,6-anhydro)-D-galactosidases et leur utilisation pour hydrolyser des polysaccharides. Brevet français N° BNT222046PC00 (17/11/2016).

Brown, green and red macroalgae (commonly referred to as seaweeds) dominate the primary production in coastal ecosystems and represent a huge biomass which is mainly constituted of polysaccharides. These diverse and complex polymers essentially differ from land plant polysaccharides. Notably, seaweeds are characterized by their abundance in uronic and sulfated polysaccharides: alginates and fucoidans in brown algae; ulvans in green algae; agars, porphyrans and carrageenans in red algae. Such sulfated polysaccharides are absent in land plants and are reminiscent of the sulfated glycosaminoglycans from the extracellular matrix of animals. Some algal polysaccharides are already used in industries as thickeners and gelling agents (e.g. alginates, agars, carrageenans). These biomolecules display also interesting biological activities (e.g. immune-stimulant, anti-viral, anti-coagulant). Despite these promising properties, algal biomass is underexploited and high value products based on algal polysaccharides and oligosaccharides remain rare. The main bottleneck for the development of a seaweed-based bioeconomy is the lack of enzymes which can specifically cleave algal polysaccharides or modify their structure, and thus allow the tailoring of their biological properties. Indeed, commercial enzymes essentially originate from terrestrial organisms which degrade plant biomass and thus are inefficient or inactive on algal biomass. Although few specific enzymes were discovered the last years (mainly due to the efforts of our group), the pathways for the biodegradation of algal polysaccharides remain largely uncharacterized. The most relevant sources of specific enzymes are marine bacteria which feed on seaweeds and thus naturally “crack” algal biomass. Among these microorganisms, marine flavobacteria are recognized as the key players in the recycling of seaweeds. In the context of the emergence of blue biotechnologies in France, the BLUE ENZYMES project aims at discovering novel enzymes from marine flavobacteria involved in the bioconversion of algal polysaccharides, using a multidisciplinary strategy combining catabolic and transcriptomic profiling, comparative genomics and reconstruction of metabolic networks. The most promising candidate enzymes will be overexpressed in Escherichia coli using a medium throughput approach. After an activity screening step using algal polysaccharides and oligosacccharides, the novel active enzymes will be studied in depth at both the biochemical and structural level. Our consortium will focus on three key genera of marine flavobacteria, Zobellia, Mariniflexile and Tenacibaculum. As preliminary results, we have already sequenced the genome of 28 species (5 Zobellia, 5 Mariniflexile and 18 Tenacibaculum) which will be exploited in BLUE ENZYMES.