have been shown to control gene expression in response to tensions, and some of these are required for virulence or persistence in vivo. function, was significantly increased in the mutant. We found that the manifestation of is stable throughout log phase and stationary phase but that it declines rapidly with o2 depletion. Inside a mouse illness model, the mutant strain was attenuated, with variations in survival and the inflammatory response in the lung between mice infected with the mutant and those infected with the crazy type. is an obligate mammalian pathogen that is believed to infect roughly one-third of the world’s human population (33). While capable of causing disease in a substantial proportion of those infected, resulting in approximately eight million instances of active tuberculosis on the planet each yr, this bacillus causes an asymptomatic illness in most individuals. After an initial period of quick replication, the infection is typically contained from the sponsor immune system, resulting in the apparent eradication of the illness in some individuals but in 58-61-7 the persistence of small numbers of bacteria in others, resulting in asymptomatic chronic infections. These latent infections may consequently become active, often in the setting of decreased host immunity, with increased bacterial replication and considerable tissue damage. During these several stages of contamination, encounters a changing host environment, in response to which the bacillus must activate defense and repair mechanisms and reprogram its physiology to ensure survival. The large number of putative transcription regulators recognized in the genome sequence indicate that much of the regulation required for these adaptations by occurs at the level of transcription (6). Among the transcription regulators that have been implicated in these processes are the option sigma factors of this organism, 12 of which are encoded in the genome. In previous work, our laboratory and others have implicated several option sigma factors in the mycobacterial response to a variety of stresses, most notably oxidative stress (13, 17-19, 24, 34). A role for option sigma factor-regulated gene expression in stationary-phase adaptation and in vivo replication in late-stage infections in mice has also been exhibited (5, 11). In addition to oxidative and nitrosative stresses, in vitro models of contamination and latency have focused on two environmental conditions that are thought to be encountered by during contamination, i.e, nutrient limitation (starvation) and hypoxia. A shift in carbon source utilization requiring the enzyme isocitrate lyase has been associated with the ability of to persist in vivo (20). Similarly, an intact gene, encoding ppGpp synthase, which is required for the induction of the stringent response, has been shown to be essential for the in vivo persistence of in mice (8). The expression of appears to be linked to the stringent response, with an increased expression in response to starvation that is at least partly Rel dependent (3, 8). Microarray data have demonstrated substantial, though incomplete, similarities between the Rabbit Polyclonal to VEGFR1 transcription profiles 58-61-7 produced in response to hypoxia, sublethal concentrations of nitric oxide, and macrophage contamination (26, 27, 31). In contrast, these transcription responses show little overlap with starvation- or stringent response-induced alterations in transcription. These data suggest that both hypoxia and starvation are important for survival in vivo but that they provoke unique physiologic adaptations that may be relevant at different stages of the dynamic process of contamination by option sigma factor SigD. After building a deletion (virulence. Based on the identity of genes that it regulates, its effects on global transcription, and the response of its gene to starvation and hypoxia, our data show that this 58-61-7 sigma factor plays a role in optimal growth both under nutrient replete conditions and, paradoxically, in response to starvation. These data suggest that SigD, while nonessential for viability in vitro, may play a role at several stages during contamination to optimize bacterial replication and survival. MATERIALS AND METHODS Bacterial strains and culture conditions. H37Rv was used as the parental strain for generating an isogenic strain and as the wild type (wt) for all those experiments. DH5 (Life Technologies) and XL1 Blue (Stratagene) were used as host strains for cloning experiments. strain mc2-155 or its derivatives were utilized for all experiments including this mycobacterial species (29). and were grown in flasks with shaking or as standing cultures.