Project description:Arabinose and galactose are major components of both particulate and dissolved organic matter. They often constitute polysaccharides such as arabinogalactan. Field studies have demonstrated a turnover of arabinogalactan, but enzymes and organisms involved have not been explored. In this study, the degradation of arabinogalactan by the marine flavobacterium Maribacter sp. MAR_2009_72 was investigated with growth experiments and proteomic analyses. Growth of Maribacter sp. MAR_2009_72 on arabinogalactan displayed its ability to utilize arabinogalactan. Proteomic analysis of cells grown on arabinogalactan, arabinose, galactose or glucose revealed expression of specific proteins in presence of arabinogalactan, mainly glycoside hydrolases. Candidates for extracellular glycan hydrolysis are five alpha-L-arabinofuranosidases affiliating with glycosyl hydrolase (GH) families 43 and 51, four unsaturated rhamnogalacturonyl hydrolases (GH105) and a protein with a glycosyl hydrolase family like domain. We detected expression of three induced TonB-dependent SusCD transporter systems, one SusC and nine glycosyl hydrolases with a predicted periplasmatic location. These are affiliated with the families GH3, GH10, GH29, GH31, GH67, GH78 and GH115. The genes are located within three canonical polysaccharide utilization loci (PUL), but also outside of the defined loci. PULs can be classified as specific for arabinogalactan, galactose-containing glycans and for arabinose-containing glycans. The breadth of enzymatic functions expressed in Maribacter sp. MAR_2009_72 as response to arabinogalactan from terrestrial plant larch suggests that Flavobacteriia are main catalysts of the rapid turnover of arabinogalactans in the marine environment.
