During infection, the nanAB operon was found to be upregulated in pneumonia and meningitis compared to growth in blood [24, 25]. Much less information is available on the nanC operon, except for the analysis of the enzymatic function of the sialidase NanC [20] and its recent implication as an alternative system for

the uptake of sialic acid [23]. The present work aims at performing a functional analysis of the operon in order to gain further insight into the metabolic regulation of this locus. Results The NanAB locus conservation in oral streptococci As a first approach SIS3 nmr to elucidate the metabolic relevance and regulation of the different predicted transcriptional units of the nanAB regulon, we performed a genomic comparison amongst related streptococcal species, including pneumococcal strain G54, S. mitis B6, S. oralis Uo5, S. sanguis BMS 907351 SK36 and S. gordonii V288 (Figure 1A and Table 1). With respect to S. PR-171 supplier pneumoniae G54, S. mitis B6 and S. oralis Uo5, these showed an identical organization for part of the locus including the neuraminidase

A (nanA), the orthologs of the satABC transporter SPG1589-91 and the genomic regions encoding the transcriptional regulator and orthologues of the enzymes involved in the first steps of sialic acid metabolism, i.e. N-acetylneuraminate lyase and N-acetylmannosamine kinase (Figure 1). In contrast to pneumococci these two species, S. mitis and S. oralis, did not possess the sialidase NanB, the second ABC transporter SPG1596-8, and the PTS system. In contrast to S. mitis and S. oralis, S. Doxorubicin cell line gordonii V288 and S. sanguinis SK36 did not possess any neuraminidases. Interestingly both S. gordonii and S. sanguis still possess orthologs of the N-acetylneuraminate lyase, N-acetylmannosamine kinase and N-acetylmannosamine-6-phosphate 2-epimerase predicted to be necessary for metabolism of sialic acid (Figure 1A,B; Table 1). In addition, S. gordonii and S. sanguis possessed the transcriptional regulator

and the orthologs of the pneumococcal SPG1596-8 ABC transporter. In contrast to S. pneumoniae, S. gordonii and S. sanguis possess neither the PTS system nor the SPG1589-91 satABC transporter. To check the amino sugar metabolism of these three different species of streptococci growth curves and fermentation assay on NeuNAc and ManNAc were performed. The growth curves show that S. gordonii grows only in presence of ManNAc, while S. mitis and S. pneumoniae are capable of growth on both amino sugars (Figure 2A,C). Similarly in the fermentation assay only S. gordonii acidified efficiently the medium in presence of ManNAc, while both S. pneumoniae and S. mitis metabolised efficiently only NeuNAc, with some acidification of the medium with ManNAc by the pneumococcus (Figure 2D). Figure 1 Structure of the neuraminidase locus in different streptococci. A. The schematic maps of the nanAB operon of S. pneumoniae G54 and the orthologous locus in its close relatives, including S.