Biosynthesis and Function of Long Guluronic Acid-blocks in Alginate produced by Azotobacter vinelandii

With the present accessibility of algal raw material, microbial alginates as a source for strong gelling material are evaluated as an alternative for advanced applications. Recently, we have shown that alginate from algal sources all contain a fraction of very long G-blocks (VLG) i.e. consecutive sequences of guluronic acid (G) residues of more than 100 residues. By comparing the gelling properties of these materials with in vitro epimerized poly-mannuronic acid (poly-M) with shorter G- blocks but comparable with the G-content, we could demonstrate that VLG have a large influence on gelling properties. Hypothesized to function as reinforcement bars, VLG prevents the contraction of the gels during formation (syneresis) and increases the Young's modulus (strength of the gel). Here we report that these VLG structures are also present in alginates from Azotobacter vinelandii and that these polymers consequently form stable, low syneretic gels with calcium, comparable in mechanical strength to algal alginates ...