Fig. 2. The α-glucan-PUL encoded SusDs cluster in two groups defined by residues in binding positions.

Alignment of sequences from isolated North Sea Flavobacteriia and MAGs from the 2020 spring bloom at Helgoland Roads. Shown are residues in positions that were characterized as substrate binding in B. thetaiotaomicron SusD²⁵ (gray). Two groups, looped (blue) and open (yellow), were defined by two residues in binding position (dark gray) that are conserved in looped α-glucan SusD-like proteins but absent in open α-glucan SusD-like proteins. MAG sequences are highlighted in bold. An asterisk marks sequences that were found highly expressed in 2020 bloom metatranscriptomes. Conservation of amino acids at their position is represented as bars on top. Numbering corresponds to amino acids of B. thetaiotaomicron SusD.