BROWN ALGAE POLYSACCHARIDE ASSIMILATION POTENTIAL IN SUBANTARCTIC SEDIMENTS

DIONISI, H. M.

Parantá, Entre Ríos

Congreso; LIV Reunión SAIB 2018; 2018

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Polysaccharides are the most abundant and structurally diverse organic molecules in the oceans, and these resources are widely exploited by marine bacteria. Brown algae dominate high-latitude coastal environments, and part of their dead biomass rich in polysaccharides is buried in the sediments, where heterotrophic bacteria participate in its decomposition. These microorganisms represent an important component of the carbon cycle in cold coastal environments, as the degradation of the brown algae biomass by sediments bacteria prevents the long term carbon sequestration in the buried biomass. However, the mechanisms that marine bacteria use for the assimilation of these polysaccharides are poorlyunderstood, in particular in yet-uncultured and difficult to cultivate taxa. At the Environmental Microbiology Laboratory of CESIMARCONICET, we are using metagenomic approaches to study the potential of sediment microbial communities to assimilate brown algae polysaccharides in Ushuaia Bay, a low-energy environment located within the Beagle Channel in Tierra del Fuego, Argentina. We analyzed the bacterial populations with the potential to degrade alginate, lineal polysaccharide that constitutes up to 40% of the brown algae biomass, using putative alginate lyase genes as biomarkers. These sequences were very abundant in a metagenomic dataset of Ushuaia Bay intertidal sediments (0.7 Gb), representing 1 every ~2,700 sequences. They belonged to 6 of the 7 polysaccharide lyase families (CAZy) described so far that include alginate lyase enzymes (in order of abundance, PL6 > PL7 > PL5 > PL14 > PL15 > PL17).The sequences were highly diverse within each family, and although 60% of them did not cluster with CAZymes, the overall tridimensional structure was similar to members of the family. The scaffolds containing putative alginate lyase sequences were assigned to 10 different phyla, with Bacteroidetes, Proteobacteria, Planctomycetes, Actinobacteria and Verrucomicrobia being the most abundant. Using the same approach, we analyzed the potential to degrade fucoidans in the sediments, which are branched polysaccharides containing mostly L-fucose and sulfate ester groups. Putative fucoidanase sequences were lessabundant (1 every ~97,600 sequences), although they were probably underestimated due to the lack of sequence information for this enzyme (GH107, 8 sequences from 4 bacterial strains).These results provide a community-wide profile of the capability to degrade two abundant components of brown algae, and constitute the basis for the enzymatic characterization of novel CAZymes from uncultured bacteria, with various biotechnological applications such as the production of oligosaccharides with bioactive properties.