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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
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
E consensus sequences. AlgU is the A. vinelandii alternative
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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