Genetic analysis of the transcriptional arrangement of Azotobacter vinelandii alginate biosynthetic genes: identification of two independent promoters

Authors

  • Lourdes Lloret,

    1. Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónorna de México, Apartado Postal 510-3, Cuemavaca 62250 Morelos, México.
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  • Rita Barreto,

    1. Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónorna de México, Apartado Postal 510-3, Cuemavaca 62250 Morelos, México.
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  • Renato León,

    1. Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónorna de México, Apartado Postal 510-3, Cuemavaca 62250 Morelos, México.
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  • Soledad Moreno,

    1. Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónorna de México, Apartado Postal 510-3, Cuemavaca 62250 Morelos, México.
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  • Jaime MartÍnez-Salazar,

    1. Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónorna de México, Apartado Postal 510-3, Cuemavaca 62250 Morelos, México.
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  • Guadalupe Espín,

    1. Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónorna de México, Apartado Postal 510-3, Cuemavaca 62250 Morelos, México.
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  • Gloria Soberón-Chávez

    Corresponding author
    1. Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónorna de México, Apartado Postal 510-3, Cuemavaca 62250 Morelos, México.
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Summary

The study of alginate biosynthesis, the exopolysac charide produced by Azotobacter vinelandii and Pseudomonas aeruginosa, might lead to different bio-technological applications. Here we report the cloning of A. vinelandii algA, the gene coding for the bifunctional enzyme phosphomannose isomerase-guano-sine diphospho-D-mannose pyrophosphorylase (PMI-GMP). This gene was selected by the complementation for xanthan gum production of Xanthomonas campestris pv. campestris xanB mutants, which lack this enzymatic activity. The complementing cosmid clones selected, besides containing algA, presented a gene coding for an alginate lyase 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. aeruginosa, A. vinelandii has a cluster of the biosynthetic alginate genes. We provide evidence for the presence of an algD-independent promoter 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.

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