Transcription of Sialic Acid Catabolism Genes in Corynebacterium glutamicum Is Subject to Catabolite Repression and Control by the Transcriptional Repressor NanR.
Corynebacterium glutamicum metabolizes sialic acid (Neu5Ac) to fructose-6-phosphate (fructose-6P) via the consecutive activity of the sialic acid importer SiaEFGI, N-acetylneuraminic acid lyase (NanA), N-acetylmannosamine kinase (NanK), N-acetylmannosamine-6P epimerase (NanE), N-acetylglucosamine-6P deacetylase (NagA), and glucosamine-6P deaminase (NagB). Within the cluster of the three operons nagAB, nanAKE, and siaEFGI for Neu5Ac utilization a fourth operon is present, which comprises cg2936, encoding a GntR-type transcriptional regulator, here named NanR. Microarray studies and reporter gene assays showed that nagAB, nanAKE, siaEFGI, and nanR are repressed in wild-type (WT) C. glutamicum but highly induced in a ΔnanR C. glutamicum mutant. Purified NanR was found to specifically bind to the nucleotide motifs A[AC]G[CT][AC]TGATGTC[AT][TG]ATGT[AC]TA located within the nagA-nanA and nanR-sialA intergenic regions. Binding of NanR to promoter regions was abolished in the presence of the Neu5Ac metabolism intermediates GlcNAc-6P and N-acetylmannosamine-6-phosphate (ManNAc-6P). We observed consecutive utilization of glucose and Neu5Ac as well as fructose and Neu5Ac by WT C. glutamicum, whereas the deletion mutant C. glutamicum ΔnanR simultaneously consumed these sugars. Increased reporter gene activities for nagAB, nanAKE, and nanR were observed in cultivations of WT C. glutamicum with Neu5Ac as the sole substrate compared to cultivations when fructose was present. Taken together, our findings show that Neu5Ac metabolism in C. glutamicum is subject to catabolite repression, which involves control by the repressor NanR.



Neu5Ac utilization is currently regarded as a common trait of both pathogenic and commensal bacteria. Interestingly, the nonpathogenic soil bacterium C. glutamicum efficiently utilizes Neu5Ac as a substrate for growth. Expression of genes for Neu5Ac utilization in C. glutamicum is here shown to depend on the transcriptional regulator NanR, which is the first GntR-type regulator of Neu5Ac metabolism not to use Neu5Ac as effector but relies instead on the inducers GlcNAc-6P and ManNAc-6P. The identification of conserved NanR-binding sites in intergenic regions within the operons for Neu5Ac utilization in pathogenic Corynebacterium species indicates that the mechanism for the control of Neu5Ac catabolism in C. glutamicum by NanR as described in this work is probably conserved within this genus.
Institute of Biochemistry, Department of Chemistry, University of Cologne, Cologne, Germany.
Andreas
A
Uhde
Institute of Biochemistry, Department of Chemistry, University of Cologne, Cologne, Germany.
Natalie
N
Brühl
Institute of Biochemistry, Department of Chemistry, University of Cologne, Cologne, Germany Institute of Microbiology & Biotechnology, Faculty of Natural Sciences, Ulm University, Ulm, Germany.
Oliver
O
Goldbeck
Chair of Genetics of Prokaryotes, Faculty of Biology & Center for Biotechnology, Bielefeld University, Bielefeld, Germany.
Christian
C
Matano
Institute of Microbiology & Biotechnology, Faculty of Natural Sciences, Ulm University, Ulm, Germany.
Oksana
O
Gurow
Institute for Genome Research and Systems Biology, Center for Biotechnology, Bielefeld University, Bielefeld, Germany.
Christian
C
Rückert
Institute of Biochemistry, Department of Chemistry, University of Cologne, Cologne, Germany.
Kay
K
Marin
Chair of Genetics of Prokaryotes, Faculty of Biology & Center for Biotechnology, Bielefeld University, Bielefeld, Germany.
Volker F
VF
Wendisch
Institute of Biochemistry, Department of Chemistry, University of Cologne, Cologne, Germany.
Reinhard
R
Krämer
Institute of Biochemistry, Department of Chemistry, University of Cologne, Cologne, Germany Institute of Microbiology & Biotechnology, Faculty of Natural Sciences, Ulm University, Ulm, Germany gerd.seibold@uni-ulm.de.
Gerd M
GM
Seibold
D000117:Acetylglucosamine / Q000031:analogs & derivatives; D048230:Corynebacterium glutamicum / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D005944:Glucosamine / Q000378:metabolism; D008360:Mannosephosphates; D008660:Metabolism; D019158:N-Acetylneuraminic Acid / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding
C430285:2-acetamido-2-deoxy-mannose-6-phosphate; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D008360:Mannosephosphates; C010004:N-acetylglucosamine 6-phosphate; D019158:N-Acetylneuraminic Acid; D005944:Glucosamine; D000117:Acetylglucosamine