One of the genes up-regulated at late-log growth phase was the locus BMEI0402. BKM120 The product of this gene has not yet been characterized in B. melitensis;

however, it has high homology (63% sequence identity) to an immunogenic outer membrane protein, Omp31 (BMEII0844) [37]. Omp31 is a haemin-binding protein [38], which binds to, and extracts iron from, the host. Iron has been identified as a required element for epithelial invasion in microbial pathogens [39–41], and the expression of this locus, along with other iron-related genes in late-log phase cultures (BMEI0176–0177, BMEII0536, BMEII0567, BMEII0583, BMEII0704, BMEII0883, BMEII1120, BMEII1122), may influence the internalization ability of brucellae. SP41 is another surface-exposed outer membrane protein with a critical role in Brucella suis adherence to, and invasion of, non-phagocytic cells [13]. The role of this protein, which is encoded by the ugpB gene (BMEII0625) present in the chromosome

II of B. melitensis 16 M genome, was not previously described for B. melitensis FK228 adhesion to and/or penetration of epithelial cells. The transcript from the ugpB gene was not identified as differentially expressed in our cDNA microarray analysis between the most and the least invasive cultures. Therefore, under our experimental I-BET151 conditions, this OMP seems not to be involved in the higher invasiveness of the late-log phase cultures. It is possible that the composition of the cell culture medium does not induce the expression of ugpB, or it is also possible that ugpB is constitutively expressed and/or act in concert with other factors. Although genetic analysis reveals that ugpB may belong to an operon (BMEII0621 to II0625) that encodes for a sn-glycerol-3-phosphate ABC transporter [42], the experimental evidence does not support this hypothesis. A previous study showed that

the product of ugpB in B. suis is indeed a surface-exposed protein with adhesion and invasion activity [13]. In fact, in this study, three of the transcripts predicted to encode the transport system [ugpC (BMEII00621) (ATP-binding thiprotein), ugpE (BMEII0622) and ugpA (BMEII0624) (permease proteins)] were highly up-regulated (> 50 fold) in late-log phase cultures, when compared to stationary Cediranib (AZD2171) phase cultures. In concordance with previous experimental evidence, our microarray data would support the finding of others that ugpB does not belong to an operon that encodes for a sn-glycerol-3-phosphate ABC transporter. In addition, our results support growth-phase regulation of the sn-glycerol-3-phosphate ABC transport system, which has been implicated in Brucella pathogenesis [24, 43]. The ability of Brucella to invade host cells is linked to its OM properties. B. melitensis OMP profile changes during culture growth [44], as gene expression is transcriptional regulated by environmental conditions [12, 45].