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Journal of Bacteriology, January 1999, p. 47-54, Vol. 181, No. 1
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Convergent Pathways for Utilization of the Amino Sugars N-Acetylglucosamine, N-Acetylmannosamine, and N-Acetylneuraminic Acid by Escherichia coli

Jacqueline Plumbridge1,* and Eric Vimr2

Institut de Biologie Physico-chimique (UPR9073), 75005 Paris, France,1 and Departments of Pathobiology and Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 618022

Received 10 August 1998/Accepted 21 October 1998

N-Acetylglucosamine (GlcNAc) and N-acetylneuraminic acid (NANA) are good carbon sources for Escherichia coli K-12, whereas N-acetylmannosamine (ManNAc) is metabolized very slowly. The isolation of regulatory mutations which enhanced utilization of ManNAc allowed us to elucidate the pathway of its degradation. ManNAc is transported by the manXYZ-encoded phosphoenolpyruvate-dependent phosphotransferase system (PTS) transporter producing intracellular ManNAc-6-P. This phosphorylated hexosamine is subsequently converted to GlcNAc-6-P, which is further metabolized by the nagBA-encoded deacetylase and deaminase of the GlcNAc-6-P degradation pathway. Two independent mutations are necessary for good growth on ManNAc. One mutation maps to mlc, and mutations in this gene are known to enhance the expression of manXYZ. The second regulatory mutation was mapped to the nanAT operon, which encodes the NANA transporter and NANA lyase. The combined action of the nanAT gene products converts extracellular NANA to intracellular ManNAc. The second regulatory mutation defines an open reading frame (ORF), called yhcK, as the gene for the repressor of the nan operon (nanR). Mutations in the repressor enhance expression of the nanAT genes and, presumably, three distal, previously unidentified genes, yhcJIH. Expression of just one of these downstream ORFs, yhcJ, is necessary for growth on ManNAc in the presence of an mlc mutation. The yhcJ gene appears to encode a ManNAc-6-P-to-GlcNAc-6-P epimerase (nanE). Another putative gene in the nan operon, yhcI, likely encodes ManNAc kinase (nanK), which should phosphorylate the ManNAc liberated from NANA by the NanA protein. Use of NANA as carbon source by E. coli also requires the nagBA gene products. The existence of a ManNAc kinase and epimerase within the nan operon allows us to propose that the pathways for dissimilation of the three amino sugars GlcNAc, ManNAc, and NANA, all converge at the step of GlcNAc-6-P.

* Corresponding author. Mailing address: Institut de Biologie Physico-chimique (UPR9073), 13, rue Pierre et Marie Curie, 75005 Paris, France. Phone: 33 01 43 25 26 09. Fax: 33 01 40 46 83 31. E-mail: plumbridge{at}ibpc.fr.

Journal of Bacteriology, January 1999, p. 47-54, Vol. 181, No. 1
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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Copyright © 1999 by the American Society for Microbiology. All rights reserved.