Diatom exudate sulfated α-1,3-mannan structures determine specific bacterial colonization in surface ocean microbiome (microbiomejournal.biomedcentral.com)

• Diatom-derived sulfated α-1,3-mannan structure resolved by NMR and chemical synthesis.
• Specialized Bacteroidota use a four-enzyme cascade for mannan degradation.
• Mannan utilization loci are globally abundant in surface ocean metagenomes and correlate with diatom blooms.
• Enzyme-based quantification reveals mannan production up to 842 µg/L and rapid consumption by Polaribacter.
• The interaction represents a chemically defined host-microbe association mediated by a single polysaccharide.

"This research identifies a C6-sulfated α-1,3-mannan exuded by diatoms that serves as a selective carbon source for adapted Polaribacter bacteria. The structure was resolved using NMR spectroscopy, chemical synthesis, and enzymatic dissection. A four-enzyme pathway in specialized Bacteroidota degrades this glycan. Metagenomic data show that sulfated mannan utilization loci are globally abundant in surface ocean bacterioplankton. The mannan provides only carbon, oxygen, sulfur, and hydrogen, reinforcing metabolic interdependence. This defines a chemically specific interaction between diatoms and bacteria mediated by a single sulfated polysaccharide."