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Journal of Bacteriology, September 2000, p. 4829-4835, Vol. 182, No. 17
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Inactivation of the ampDE Operon Increases Transcription of algD and Affects Morphology and Encystment of Azotobacter vinelandii

Cinthia Núñez, Soledad Moreno, Luis Cárdenas, Gloria Soberón-Chávez, and Guadalupe Espín*

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

Received 7 March 2000/Accepted 1 June 2000

Transcription of algD, encoding GDP-mannose dehydrogenase, the key enzyme in the alginate biosynthetic pathway, is highly regulated in Azotobacter vinelandii. We describe here the characterization of a Tn5 insertion mutant (AC28) which shows a higher level of expression of an algD::lacZ fusion. AC28 cells were morphologically abnormal and unable to encyst. The cloning and nucleotide sequencing of the Tn5-disrupted locus in AC28 revealed an operon homologous to the Escherichia coli ampDE operon. Tn5 was located within the ampD gene, encoding a cytosolic N-acetyl-anhydromuramyl-L-alanine amidase that participates in the intracellular recycling of peptidoglycan fragments. The ampE gene encodes a transmembrane protein, but the function of the protein is not known. We constructed strains carrying ampD or ampE mutations and one with an ampDE deletion. The strain with a deletion of the ampDE operon showed a phenotype similar to that of mutant AC28. The present work demonstrates that both alginate production and bacterial encystment are greatly influenced by the bacterial ability to recycle its cell wall.

* 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: 52-73-114692. Fax: 52-73-172388. E-mail: espin{at}ibt.unam.mx.

Journal of Bacteriology, September 2000, p. 4829-4835, Vol. 182, No. 17
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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