Catalyzes the oxidation of guanosine diphospho-D-mannose (GDP-D-mannose) to GDP-D-mannuronic acid, a precursor for alginate polymerization. The alginate layer causes a mucoid phenotype and provides a protective barrier against host immune defenses and antibiotics (Probable). Other sugars are not used as substrates (PubMed:2470755). GDP-alpha-D-mannose + H2O + 2 NAD(+) = GDP-alpha-D-mannuronate + 3 H(+) + 2 NADH Inhibited by GMP, ATP, GDP-D-glucose and maltose (PubMed:2470755). Inhibited by GMP and deamidoNAD (PubMed:12135385). Optimum pH is 7.7. Optimum temperature is 50 degrees Celsius. Stable at 57.5 degrees Celsius, pH 5.0 for 10 minutes, used to purify protein. Glycan biosynthesis; alginate biosynthesis. Forms a domain-swapped dimer with each peptide contributing to each active site. The dimers assemble further (PubMed:12705829). X-ray structures indicate this enzyme exists as a homotetramer PubMed:12705829, but kinetic and physical results obtained in PubMed:2470755 and PubMed:12135385 indicate that it is probably a homohexamer (Probable). Highly expressed in mucoid but not non-mucoid cells, probably activated by algR. The N-terminus (about 270 residues) binds NAD(+) and GDP-alpha-D-mannose and is joined to C-terminal domain by an exposed linker. Belongs to the UDP-glucose/GDP-mannose dehydrogenase family. Slime with a design - Issue 37 of August 2003