Genomic Analyses of Polysaccharide Utilization in Marine Flavobacteriia

Marine algae convert a substantial fraction of fixed carbon dioxide into various polysaccharides. Flavobacteriia that are specialized on algal polysaccharide degradation feature genomic clusters termed polysaccharide utilization loci (PULs). Since knowledge on extant PUL diversity is sparse, we sequenced the genomes of 53 North Sea Flavobacteriia. We obtained 400 PULs, suggesting usage of a large array of polysaccharides, including laminarin, A A /-- and A A -mannans, fucose-, xylose-, galactose-, rhamnose- and arabinose-containing substrates, pectins, and chitins. Many of the PULs exhibit new genetic architectures and suggest substrates rarely described for marine environments. The isolates' PUL repertoires often differed considerably within genera, corroborating ecological niche-associated glycan partitioning. Polysaccharide uptake in Flavobacteriia is mediated by SusCD-like transporter complexes. Respective protein trees revealed clustering according to polysaccharide specificities predicted by PUL annotations rather than phylogenetic affiliation. Using the trees, we analyzed expression of SusC/D homologs in multiyear phytoplankton bloom-associated metaproteomes and found indications for profound changes in microbial utilization of laminarin, A A /--glucans, ß-mannan and sulfated xylan. We hence suggest the suitability of SusC/D-like transporter protein expression within heterotrophic bacteria as a proxy for the temporal utilization of discrete polysaccharides.