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.

Abstract

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.

• Authors: Magnus Steigedal, Håvard Sletta, Soledad Moreno, Mali Maerk, Bjørn E Christensen, Tonje Bjerkan, Trond Erling Ellingsen, Guadalupe Espìn, Helga Ertesvåg, Svein Valla
• Journal: Environmental microbiology (Environ Microbiol) Vol. 10 Issue 7 Pg. 1760-70 (Jul 2008) ISSN: 1462-2920 [Electronic] England
• PMID: 18373676 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

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

Topics

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