Therefore, the highly connected nodes in these networks, the hubs, represented GSK872 chemical structure genes

that were differentially expressed under many conditions or which had several functions in the cell. Our analysis was based on data extracted from three different strains of Salmonella, and we cannot rule out that details may differ between the three strains. However, the general scape of the networks should remain strain independent. Network analysis was based in the genome of S. Typhimurium LT2 strain, which was different from the strains used to evaluate the stress response and to carry out mutations. However, a highly similarity in the genome composition of S. Typhimurium strains has been previously reported [21, 22]. For instance, the magnitude of the reported difference between S. Typhimurium strains was in one case of two genes located in prophages [21] while in another study GSK126 cost the similarity was higher than 98% with the greatest difference attributable again to the distribution of prophages

[22]. Hubs are considered the strength of scale-free networks from random failures and their Achilles’ heel for directed attacks [16]. In order to investigate whether hubs were formed by essential genes in bacterial selleck screening library cellular networks, we carried out directed attacks by mutation of selected hubs in both Network 2 and Network 3. This showed that deletion of genes that formed hubs in these networks did not affect growth, stress adaptation or virulence. Despite the proven essentiality of hubs in other networks, hubs do not seem to be indispensable in cellular networks. This makes cellular networks more resistant to directed attacks addressing the weakest point of the scale free topology. This conclusion was based on analyses of four out of the five most connected genes in both types of network and a limited number of stresses, and we cannot rule out that mutation affects Tolmetin adaptation to stresses that we have

not assessed. To aid the reader in evaluation of result, a short description of our results in the light of the current knowledge of the five most connected genes in both networks is included below. The wraB gene of S. Typhimurium encodes the WrbA protein eliciting 94% sequence similarity to the E. coli WrbA protein [23]. WrbA was first suggested to be involved in the binding of the tryptophan repressor to the operator [24] and recently identified as a novel flavoprotein [25] with NAD(P)H-dependent redox activity and able to reduce quinones. It has been designated as a NAD(P)H:quinone oxidoreductase (NQO) type IV which are associated with oxidative stress [26]. However, in the current investigation, a wraB single mutant was found not to show any changes in phenotype under any of the tested conditions, including when subjected to oxidative stress by H2O2.