GENETIC-ANALYSIS OF THE TRANSCRIPTIONAL ARRANGEMENT OF AZOTOBACTER-VINELANDII ALGINATE BIOSYNTHETIC GENES - IDENTIFICATION OF 2 INDEPENDENTPROMOTERS

The study of alginate biosynthesis, the exopolysaccharide produced by Azotobacter vinelandii and Pseudomonas aeroginosa, might lead to diffe rent biotechnological applications, Here we report the cloning of A, v inelandii algA, the gene coding for the bifunctional enzyme phosphoman nose isomerase-guanosine diphospho-D-mannose pyrophosphorylase (PMI-GM P), This gene was selected by the complementation for xanthan gum prod uction of Xanthomonas campestris pv, campestris xanB(-) mutants, which lack this enzymatic activity, The complementing cosmid clones selecte d, besides containing algA, presented a gene coding for an alginate ly ase activity (algL), and some of them also contained algD which codes for GDP-mannose dehydrogenase. We present here the characterization of the A. vinelandii chromosomal region comprising algD and its promoter region, algA and algL, showing that, as previously reported for P. ae roginosa, A. vinelandii has a cluster of the biosynthetic alginate gen es, We provide evidence for the presence of an algD-independent promot er in this region which transcribes at least algL and algA, and which is regulated in a manner that differs from that of the algD promoter.