Journal Article

Sulfated mannan of diatoms selects host-specific microbiota in the sunlit ocean

Teeling, H., Singh, R. K., Crawford, C. J., Solanki, V., Sidhu, C., Robb, C. S., Rößler, L., Schweder, T., Huang, G., Seeberger, P. H., Hehemann, J.-H., Bligh, M., Krull, J.

2026

Overview

Background Diatoms, a keystone phylum in Earth’s ecosystems, are responsible for substantial oxygen production and the fixation of carbon dioxide in the form of carbohydrates that fuel global food webs. They host diverse prokaryotes, yet how diatoms preferentially recruit those with complementary metabolic traits remains unknown. Results We discovered that diatoms exude a C6-sulfated α-1,3-mannan that serves as a selective carbon source for adapted Polaribacter . Its structure was resolved using NMR spectroscopy, chromatography, chemical synthesis, and enzymatic dissection. Biochemical, physiological, and structural analyses demonstrated, that specialized Bacteroidota employ a four-enzyme pathway to metabolize this glycan. Metagenomic and transcriptomic data revealed that sulfated mannan utilization loci are globally abundant and actively expressed in surface ocean bacterioplankton. Because this mannan provides only carbon, oxygen, sulfur, and hydrogen, bacteria must obtain other essential elements elsewhere, reinforcing metabolic interdependence. Conclusions Together, these results define a chemically specific interaction between diatoms and specialized bacteria that is mediated by a single sulfated polysaccharide and a dedicated four-enzyme degradation pathway. Presence of this pathway in marine metagenomes and transcriptomes indicates that a sulfated mannan from diatoms exerts selection pressure in the sunlit ocean microbiome. 5kCwS6BEacZCaPFxt1T7DN Video Abstract

• Publisher: BioMed Central,BioMed Central Ltd,Springer Nature B.V,BMC
• Subject: Automation / Bacillariophyceae / Bacteria / Bacteria - classification / Bacteria - genetics / Bacteria - metabolism / Bacterioplankton / Bacteroidetes - genetics / Bacteroidetes - metabolism / Bioinformatics / Biomedical and Life Sciences / Biomedicine / Carbohydrates / Carbon dioxide / Carbon dioxide fixation / Carbon sequestration / Carbon sources / Chemical synthesis / Chromatography / Diatoms - chemistry / Diatoms - metabolism / Diatoms - microbiology / Enzymes / Food webs / Genomes / Host specificity / Magnetic resonance spectroscopy / Mannan / Mannans - chemistry / Mannans - metabolism / Marine microorganisms / Medical Microbiology / Metabolism / Metagenome / Metagenomics / Metagenomics - methods / Microbial Ecology / Microbial Genetics and Genomics / Microbiology / Microbiomes / Microbiota / Microbiota (Symbiotic organisms) / NMR / Nuclear magnetic resonance / Nuclear magnetic resonance spectroscopy / Ocean / Oceans and Seas / Physiological aspects / Plankton / Polysaccharides / Prokaryotes / Seawater / Seawater - microbiology / Sulfates / Sulfates - metabolism / Transcriptomes / Transcriptomics / Virology