Poly-beta-D-mannuronate (Pm) and its derivatives have potential to be used in pharmaceutical applications. A spontaneous mutant (El)) of Pseudomonas alkylphenolia KL28 produced large amounts of a highly viscous polymer consisting of repetitive units of beta-n-mannuronic acid with acetylation at the 2nd and/or 3rd carbon (AcPM). The alg gene cluster (18,275 bp with 12 ORFs) is essential for the production of AcPM and has been sequenced. Mutations in the El strain were found in both the mucA (resulting in a truncated protein) and the algG (non-synonymous amino acid substitution in the conserved epimerase domain of mannuronan C-5-epimerase) genes. Disruption of alg1 (acetylase) resulted in the production of a deacetylated polymer, PM. The molecular weight (viscosity) and the AcPM production level were influenced by the addition of NaCl into the culture media. Under optimized flask culture conditions, 8-14 g/L of AcPM with different viscosities could be produced. In addition, some rheological properties of the high molecular weight AcPM produced by the El mutant were better suited for pharmaceutical use than commercial alginate. In conclusion, P. alkylphenolia E1 and its alg1 mutant may be suitable candidates for mass production of AcPM and PM, respectively. (C) 2010 Elsevier Ltd. All rights reserved.