Regulation of alginate biosynthesis in Azotobacter vinelandii

Abstract

Alginate is a linear exopolysaccharide composed of various amount of (1-4) linked β-D mannuronic acid and its C5 epimer α-L-guluronic acid. Alginate is synthesized by two bacterial genera Azotobacter and Pseudomonas. Azotobacter vinelandii is a gram negative bacterium that can fix atmospheric nitrogen and form desiccation resistant cyst.Transcriptional activation of algD gene is a main point in regulation of alginate biosynthesis pathway in A.vinelandii. In A.vinelandii alginate biosynthesis gene cluster is organized in transcriptional units of algD promoter. AlgR, AlgB and AmrZ are the major regulators required by algD promoter for its expression. Alternative sigma factor σ22 encoded by algU directly controls the algD promoter and its expression. In this study, a vector expressing AlgW in A.vinelandii was constructed. Also, the plasmids for measuring algD expression and algC expression using mcherry as a reporter gene were constructed. Alginate production and algD gene expression was compared in strains lacking algW or algB with wildtype strain overproducing these proteins. Also, alginate was assayed enzymatically.Based on results it was found that algB controls algD not only in Pseudomonas species but also in Azotobacter. The study of effect of succinate on growth and alginate revealed that wildtype A.vinelandii has maximum growth in the medium supplemented with succinate.