It is possible that expression of these genes was repressed

when leptospires encountered the low-iron milieu in serum. Similar findings were observed in Yersinia pseudotuberculosis grown in plasma, resulting in down-regulation of several enzymes of the TCA cycle [79]. The transition of Leptospira to serum resulted in up-regulation of pyrD (LIC13433), predicted to encode a check details dihydroorotate dehydrogenase which catalyzes the fourth step in the de novo pyrimidine nucleotide biosynthetic pathway [80], possibly due to limited availability of pyrimidine in serum. This finding is consistent with previous reports showing that the scarcity of nucleotide precursors is the key limitation of bacterial growth in blood [81]. Therefore, de novo nucleotide Survivin inhibitor biosynthesis may be required for growth of leptospires in serum. However, enzymes involved in de novo biosynthesis of purine nucleotides were not induced in our study. Notably, down-regulation of one of the purine

salvage enzymes (LIC13399, predicted to encode a purine-nucleoside phosphorylase) was observed. It has been suggested that transcription of genes in purine and pyrimidine biosynthetic pathways is independently regulated [80, 81]. In addition, it is possible that differential expression of genes involved in purine biosynthesis was transient and may not show steady-state expression ratios. Therefore, these genes were not detected as differentially expressed. ICG-001 nmr In addition, coaE (LIC13085) encoding dephospho-CoA kinase, which catalyzes the final step in coenzyme A biosynthesis [82], was up-regulated in response to serum, consistent with the use of coenzyme A

as a key cofactor during serum exposure. The kdpFABC operon is typically induced under conditions of severe K+ limitation or osmotic upshift and repressed during growth in media of high external K+ concentration [83]. The putative kdpA (LIC10990) encoding the A chain of potassium-transporting ATPase was down-regulated in response to serum. However, as the level of potassium in EMJH (2.2 mM) is lower than in serum (~5.2 mM) this result is not surprising. Two leptospiral genes predicted to encode fatty acid desaturases (LIC13053 [desA] and LIC20052) were up-regulated in the presence Fossariinae of serum. The unsaturated bonds introduced into fatty acids by these enzymes have been reported to be essential for membrane lipid homeostasis to maintain the fluidity of biological membranes, especially in response to downward temperature shift [84, 85]. The ability of Leptospira to modulate its membrane lipid using fatty acid desaturases may thus be important for survival in response to environmental stresses encountered in serum. Bacterial genes of related functions, including enzymes of metabolic pathways, are frequently but not always co-transcribed as a single transcriptional unit.