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J. Bacteriol., Apr 1996, 1793-1799, Vol 178, No. 7
M Campos, JM Martinez-Salazar, L Lloret, S Moreno, C Nunez, G Espin and G Soberon- Chavez
Azotobacter vinelandii presents a differentiation process leading to the
formation of desiccation-resistant cysts. Alginate, the exopolysaccharide
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 dehydrogenase (algD),
which is the key enzyme for alginate synthesis in Pseudomonas aeruginosa.
This gene has a high degree of similarity with the algD gene from P.
aeruginosa, and similar proteins seem to be involved in algD regulation in
both bacteria. We show the existence of two mRNA start sites; one of these
sites corresponds to a promoter transcribed by RNA polymerase containing a
sigma E subunit. An A. vinelandii algD mutant which is completely impaired
in alginate production and which is unable to form desiccation-resistant
cells was constructed. The effects of NH4, NO3, and NaCl concentrations on
algD transcription for three A. vinelandii strains producing different
alginate levels were evaluated. We found a strict correlation between
alginate production and algD transcription for the three strains studied;
however, the effects on algD transcription under the conditions studied
were different for each strain. The nitrogen source regulates algD
expression in the wild-type strain.
Copyright © 1996, American Society for Microbiology
Characterization of the gene coding for GDP-mannose dehydrogenase (algD) from Azotobacter vinelandii
Departamento de Microbiologia Molecular, Instituto de Biotecnologia, Universidad Nacional Autonoma de Mexico, Morelos, Mexico.
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