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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 operonsnagAB ,nanAKE , andsiaEFGI for Neu5Ac utilization a fourth operon is present, which comprisescg2936 , encoding a GntR-type transcriptional regulator, here named NanR. Microarray studies and reporter gene assays showed thatnagAB ,nanAKE ,siaEFGI , andnanR 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 thenagA-nanA andnanR-sialA intergenic regions. Binding of NanR to promoter regions was abolished in the presence of the Neu5Ac metabolism intermediates GlcNAc-6P andN -acetylmannosamine-6-phosphate (ManNAc-6P). We observed consecutive utilization of glucose and Neu5Ac as well as fructose and Neu5Ac by WTC. glutamicum , whereas the deletion mutantC. glutamicum ΔnanR simultaneously consumed these sugars. Increased reporter gene activities fornagAB ,nanAKE , andnanR were observed in cultivations of WTC. glutamicum with Neu5Ac as the sole substrate compared to cultivations when fructose was present. Taken together, our findings show that Neu5Ac metabolism inC. glutamicum is subject to catabolite repression, which involves control by the repressor NanR.IMPORTANCE Neu5Ac utilization is currently regarded as a common trait of both pathogenic and commensal bacteria. Interestingly, the nonpathogenic soil bacteriumC. glutamicum efficiently utilizes Neu5Ac as a substrate for growth. Expression of genes for Neu5Ac utilization inC. 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 pathogenicCorynebacterium species indicates that the mechanism for the control of Neu5Ac catabolism inC. glutamicum by NanR as described in this work is probably conserved within this genus.

journal of bacteriology

Transcription of Sialic Acid Catabolism Genes in Corynebacterium glutamicum Is Subject to Catabolite Repression and Control by the Transcriptional Repressor NanR