Some of these transcription factors are known to be involved in positive regulation of gene expression (LuxR, AraC). Others are involved in repression (DeoR, MerR), while members of IclR and LysR families could be activators or repressors of gene expression [22]. Nevertheless, the contribution of these regulators and

their targets to B. melitensis internalization epithelial cells has not been fully examined. The locus encoding the alternative sigma 32 factor (BMEI0280) that allows Brucella to survive under general stress situations was up-regulated in stationary phase cultures. The BMEI1789 locus that encodes a subunit of the other alternative sigma 54 factor (rpoN), which allows transcription of those genes involved in utilization Y-27632 in vivo of nitrogen and carbon sources and energy metabolism, was up-regulated in late-log phase cultures compared to stationary phase cultures. Two-component transcriptional regulators are comprised of a cytoplasmic membrane-located sensor protein and a cytoplasmic response regulator protein [23]. Eight ORFs encoding for two-component response regulators have been identified in the B. melitensis 16 M genome [19]. Raf inhibitor review One of the signal transduction-encoded genes up-regulated in late-log phase cultures (vsr; BMEI1606), was previously identified in B. melitensis attenuated mutants [24]. The other

(hprK; BMEI2034) is a central regulator of carbohydrate metabolism genes and also plays a role in virulence development of certain pathogens [25]. Although the molecular regulation Acyl CoA dehydrogenase of these response regulators in B. melitensis is currently unknown, understanding how vsr, hprK and others are regulated, could offer insight into B. melitensis virulence. Identifying the target genes of these transcriptional regulators would significantly clarify the role of growth-phase in Brucella physiology, metabolism and virulence regulation. Almost all differentially expressed genes encoding cell envelope and outer membrane components were up-regulated in late-log phase cultures The ability of Brucella to invade cells has been linked to its outer membrane (OM) properties, as well as to structures built within

the cell envelope [26, 27]. Twenty-six genes directly involved in cell envelope and outer membrane biogenesis were differentially expressed at late-log compared to stationary phase of growth. These included genes that encode outer membrane proteins (BMEI0402, BMEI0786), lipoproteins (BMEI0991, BMEI1079), LPS (BMEI0418, BMEI0586, BMEI0833, BMEI1414), and peptidoglycan biosynthesis (BMEI0271, BMEI0576). The main COGs functional category of genes that were up-regulated in B. melitensis cultures at late-log compare to stationary phase of growth were ORFs encoding membrane transport proteins. These included genes encoding transporters specific for amino acids (BMEI0263–0264, BMEII0098–9 and BMEII0861 to II0864), carbohydrates (BMEI1580, BMEI1713, BMEII0621–2 and II0624) and uncharacterized transporters (BMEI1554, BMEII0481, BMEII0483, BMEII0662).