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The Na⁺-translocating NADH : ubiquinone oxidoreductase of Azotobacter vinelandii negatively regulates alginate synthesis

¹ Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, Col. Chamilpa, Cuernavaca, Morelos 62210, Mexico
² Department of Molecular Energetics of Microorganisms, A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119992, Russia

Correspondence
Cinthia Núñez
cinthia{at}ibt.unam.mx

Azotobacter vinelandii is a nitrogen-fixing soil bacterium that produces the exopolysaccharide alginate. In this report we describe the isolation and characterization of A. vinelandii strain GG4, which carries an nqrE : : Tn5 mutation resulting in alginate overproduction. The nqrE gene encodes a subunit of the Na⁺-translocating NADH : ubiquinone oxidoreductase (Na⁺-NQR). As expected, Na⁺-NQR activity was abolished in mutant GG4. When this strain was complemented with the nqrEF genes this activity was restored and alginate production was reduced to wild-type levels. Na⁺-NQR may be the main sodium pump of A. vinelandii under the conditions tested (2 mM Na⁺) since no Na⁺/H⁺-antiporter activity was detected. Collectively our results indicate that in A. vinelandii the lack of Na⁺-NQR activity caused the absence of a transmembrane Na⁺ gradient and an increase in alginate production.