STUDIES ON SOME ENZYMES OF ALGINIC ACID BIOSYNTHESIS IN MUCOID AND NONMUCOID AZOTOBACTER-CHROOCOCCUM STRAINS

Measurements of enzymes involved in alginate biosynthesis were straigh tforward in mucoid (alginate-positive) Azotobacter chroococcum ATCC 44 12 crude extracts. At the stationary growth phase, where the productio n of the exopolysaccharide was greatest, the enzymes phosphomannose is omerase and GDP-mannose pyrophosphorylase increased markedly, whereas phosphomannomutase and GDP-mannose dehydrogenase kept the high activit y levels measured in the acceleration growth phase. In nonmucoid (algi nate-negative) A. chroococcum and A. vinelandii strains, the activitie s of phosphomannose isomerase and GDP-mannose pyrophosphorylase were r ather low or, in some cases, undetectables. Except in A. chroococcum M CD1, which exhibited a low activity, phosphomanomutase was high in the nonmucoid Azotobacter strains, and GDP-mannose dehydrogenase reached a significant activity level in two out of four nonmucoid strains test ed. The results suggest that derepression of phophomannose isomerase a nd GDP-mannose pyrophosphorylase is a sine qua non condition for algin ate formation by A. chroococcum.