Background Typhimurium is an important pathogen of human being and animals. and cell functions. The five genes with most contacts in the transcriptional network (and proved unsuccessful. No difference between mutants and the crazy type strain was observed during growth at unfavorable temps, pH ideals, NaCl concentrations and in the presence of H2O2. Eight mutants were evaluated for virulence in C57/BL6 mice and none of them differed from your crazy type strain. Notably, however, deviations of phenotypes with respect to the crazy type were observed when combinations of these genes were erased. Summary Network analysis exposed the presence of hubs in both transcriptional and practical networks of Typhimurium. Hubs theoretically confer higher resistance to random mutation but a greater susceptibility to directed attacks, however, we found that genes that created hubs were dispensable for growth, stress adaptation and virulence, suggesting that development favors non-essential genes as main connectors in cellular networks. Background serovar Typhimurium (Typhimurium) is TNFRSF13B an important intestinal pathogen of man and animals . It normally invades the sponsor in the intestine leading to a self-limiting gastro-enteritis , but it may also cause a systemic disease in which it resides inside professional phagocytic cells . In mice it causes a Typhoid-like disease, and in this model the contribution of many genes to disease is definitely well-characterized . Studies in the closely related bacterium have demonstrated the transcriptional response to one stress-stimulus overlaps with the response to additional stimuli in a highly adaptive manner [5,6], creating an element of cross resistance towards different stress conditions. While the transcriptional reactions of Typhimurium during growth and in response to different environmental stress conditions have also been detailed [7-10], a systematic analysis of how the Typhimurium reactions interact with each other has not been performed. Network analysis is a powerful tool to analyze relationships between different matrixes . Networks representing widely different things 4682-36-4 manufacture such as sociable relations , molecular biochemical rules [13,14] and transcriptional reactions 4682-36-4 manufacture in bacteria  have all been shown to belong to the family of scale-free networks, which are characterized by the presence of hubs, i.e. highly connected nodes . Preferential attachment is definitely a mechanism that clarifies the scale-free topology, i.e. fresh nodes link preferentially with the more connected nodes or hubs . Hubs confer an exceptional robustness to networks towards random node failures; however, directed attacks towards hubs theoretically cause a major network disruption . In transcriptional network analysis of bacterial reactions to different growth conditions and different functionalities, such hubs would represent genes that are significantly controlled in response to many different conditions or which are involved in many different pathways and cell functions. From an evolutionary perspective it would be risky, if genes that form these connections were indispensable for cell functions, since mutation in one of these genes would then have effects for the ability of the bacterium to adapt to many different conditions. In the current study we performed network analysis of transcriptional reactions of Typhimurium to a number of growth and stress conditions and of the global features of products encoded in the genome. We then analyzed the topology and the functionality of the most connected genes recognized in these two networks and shown that highly connected genes indeed were dispensable for growth, stress adaptation and virulence. Hence 4682-36-4 manufacture it appeared that cellular networks of Typhimurium were not susceptible to attacks directed towards solitary hubs. Results Transcriptional response to different environmental tensions share many genes, and genes that are up-regulated at one environmental stress condition are not likely to be down-regulated as response to another condition. We constructed a microarray consisting of 425 carefully selected stress and virulence genes and used this to assess the transcriptional response of Typhimurium to warmth, 4682-36-4 manufacture osmotic, oxidative and acid stress under anoxic and oxic conditions and to non-stressed anoxic conditions. Therefore, our study was not a genome level transcriptional response analysis but it was focused on the rules of the 425 genes most relevant for stress response and virulence. The selection of the 425 genes was based in several earlier experimental evidences compiled in the GenBank database and they represent the.