The Azotobacter vinelandii AlgE mannuronan C-5-epimerase family is essential for the in vivo control of alginate monomer composition and for functional cyst formation

Environ Microbiol. 2008 Jul;10(7):1760-70. doi: 10.1111/j.1462-2920.2008.01597.x. Epub 2008 Mar 28.


The industrially widely used polysaccharide alginate is a co-polymer of beta-D-mannuronic acid and alpha-L-guluronic acid (G), and the G residues originate from a polymer-level epimerization process catalysed by mannuronan C-5-epimerases. In the genome of the alginate-producing bacterium Azotobacter vinelandii genes encoding one periplasmic (AlgG) and seven secreted such epimerases (AlgE1-7) have been identified. Here we report the generation of a strain (MS163171) in which all the algE genes were inactivated by deletion (algE1-4 and algE6-7) or interruption (algE5). Shake flask-grown MS163171 produced a polymer containing less than 2% G (algG still active), while wild-type alginates contained 25% G. Interestingly, addition of proteases to the MS163171 growth medium resulted in a strong increase in the chain lengths of the alginates produced. MS163171 was found to be unable to form functional cysts, which is a desiccation-resistant differentiated form developed by A. vinelandii under certain environmental conditions. We also generated mutants carrying interruptions in each separate algE gene, and a strain containing algE5 only. Studies of these mutants indicated that single algE gene inactivations, with the exception of algE3, did not affect the fractional G content much. However, for all strains tested the alginate composition varied somewhat as a response to the growth conditions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alginates / chemistry*
  • Alginates / metabolism
  • Azotobacter vinelandii / chemistry
  • Azotobacter vinelandii / enzymology*
  • Carbohydrate Epimerases / metabolism
  • Carbohydrate Epimerases / physiology*
  • Gene Deletion
  • Genes, Bacterial
  • Glucuronic Acid
  • Hexuronic Acids / metabolism*


  • Alginates
  • Hexuronic Acids
  • Glucuronic Acid
  • mannuronic acid
  • Carbohydrate Epimerases
  • mannuronan c-5-epimerase