CHARACTERIZATION OF THE GENE CODING FOR GDP-MANNOSE DEHYDROGENASE (ALGD) FROM AZOTOBACTER-VINELANDII

Azotobacter vinelandii presents a differentiation process leading to t he formation of desiccation resistant cysts, Alginate, the exopolysacc haride produced by this bacterium, has been postulated to have a role in cyst formation, Here, we report the cloning and characterization of the A. vinelandii gene coding for the enzyme GDP-mannose dehydrogenas e (algD), which is the key enzyme for alginate synthesis in Pseudomona s aeruginosa, This gene has a high degree of similarity with the algD gene from P. aeruginosa, and similar proteins seem to be involved in a lgD regulation in both bacteria. We show the existence of two mRNA sta rt sites; one of these sites corresponds to a promoter transcribed by RNA polymerase containing a sigma(E) subunit, An A. vinelandii algD mu tant which is completely impaired in alginate production and which is unable to form desiccation-resistant cells was constructed, The effect s of NH4, NO3, and NaCl concentrations on algD transcription for three A. vinelandii strains producing different alginate levels were evalua ted, We found a strict correlation between alginate production and alg D transcription for the three strains studied; however, the effects on algD transcription under the conditions studied were different for ea ch strain. The nitrogen source regulates algD expression in the wild-t ype strain.