Sialic acid-mediated gene expression in Streptococcus pneumoniae and the role of NanR as a transcriptional activator of the nan gene cluster

In this study, we investigated the transcriptomic response of Streptococcus pneumoniae D39 to sialic acid (N-acetylneuraminic acid: Neu5Ac). Transcriptome comparison of the D39 wild-type grown in M17 medium with and without sialic acid revealed the elevated expression of various genes and operons including the nan gene cluster (nan operon-I and nanA gene). Our microarray analysis and promoter-lacZ fusion studies showed that the transcriptional regulator NanR, acts as a transcriptional activator of nan operon-I and the nanA gene in the presence of sialic acid. The putative regulatory site of NanR in the promoter region of nan operon-I is predicted and confirmed by promoter truncation experiments. Furthermore, the role of CcpA in the regulation of the nan gene cluster is demonstrated through microarray analysis and promoter-lacZ fusion studies, suggesting that in the presence of sialic acid and glucose, CcpA represses the expression of nan operon-I while the expression of the nanA gene is CcpA-independent