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J Bacteriol, May 1998, p. 2766-2769, Vol. 180, No. 10
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Role of Alternative sigma  Factor AlgU in Encystment of Azotobacter vinelandii

Soledad Moreno, Rebeca Nájera, Josefina Guzmán, Gloria Soberón-Chávez, and Guadalupe Espín*

Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62250, México

Received 23 October 1997/Accepted 5 March 1998

Alginate is essential for encystment in Azotobacter vinelandii. Transcription of the algD gene, which codes for GDP-mannose dehydrogenase, a key enzyme in the alginate biosynthetic pathway, is initiated at two promoters, one of which, p2, has sigma E consensus sequences. AlgU is the A. vinelandii alternative sigma E factor. In this study, we constructed an algU mutant (SMU88) which, as expected, is impaired in alginate production, encystment, and transcription of the algD gene from the p2 promoter. Plasmid pJMSAT1, carrying the A. vinelandii algU gene, restored alginate production and encystment to SMU88 and to strain UW136, a naturally occurring algU mutant. Plasmid pSMU865, carrying the A. vinelandii mucABCD genes coding for negative regulators of AlgU activity and previously shown to diminish alginate production in the wild-type strain, ATCC 9046, was shown here to impair encystment and transcription of the algD gene from the p2 algU-dependent promoter. Since nonencysting strain ATCC 9046/pSMU865 produced more alginate than some encysting strains, such as UW136/pJMSAT1, we propose an AlgU role in encystment, independent of the structural role that alginate plays in mature cysts.

* Corresponding author. Mailing address: Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. postal 510-3, Cuernavaca, Morelos 62250, México. Phone: (52) (73) 291644. Fax: (52) (73) 172388. E-mail: espin{at}ibt.unam.mx.

J Bacteriol, May 1998, p. 2766-2769, Vol. 180, No. 10
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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