The enhancer binding protein Nla6 regulates developmental genes that are important for Myxococcus xanthus sporulation.

UNLABELLED: In the bacterium Myxococcus xanthus, starvation triggers the formation of multicellular fruiting bodies containing thousands of stress-resistant spores. Recent work showed that fruiting body development is regulated by a cascade of transcriptional activators called enhancer binding proteins (EBPs). The EBP Nla6 is a key component of this cascade; it regulates the promoters of other EBP genes, including a downstream-functioning EBP gene that is crucial for sporulation. In recent expression studies, hundreds of Nla6-dependent genes were identified, suggesting that the EBP gene targets of Nla6 may be part of a much larger regulon. The goal of this study was to identify and characterize genes that belong to the Nla6 regulon. Accordingly, a direct repeat [consensus, C(C/A)ACGNNGNC] binding site for Nla6 was identified using in vitro and in vivo mutational analyses, and the sequence was subsequently used to find 40 potential developmental promoter (88 gene) targets. We showed that Nla6 binds to the promoter region of four new targets (asgE, exo, MXAN2688, and MXAN3259) in vitro and that Nla6 is important for their normal expression in vivo. Phenotypic studies indicate that all of the experimentally confirmed targets of Nla6 are primarily involved in sporulation. These targets include genes involved in transcriptional regulation, cell-cell signal production, and spore differentiation and maturation. Although sporulation occurs late in development, all of the developmental loci analyzed here show an Nla6-dependent burst in expression soon after starvation is induced. This finding suggests that Nla6 starts preparing cells for sporulation very early in the developmental process. IMPORTANCE: Bacterial development yields a remarkable array of complex multicellular forms. One such form, which is commonly found in nature, is a surface-associated aggregate of cells known as a biofilm. Mature biofilms are structurally complex and contain cells that are highly resistant to antibacterial agents. When starving, the model bacterium Myxococcus xanthus forms a biofilm containing a thin mat of cells and multicellular structures that house a highly resistant cell type called a myxospore. Here, we identify the promoter binding site of the transcriptional activator Nla6, identify genes in the Nla6 regulon, and show that several of the genes in the Nla6 regulon are important for production of stress-resistant spores in starvation-induced M. xanthus biofilms.

Induction of human host cell apoptosis by Trichomonas vaginalis cysteine proteases is modulated by parasite exposure to iron.

Trichomonas vaginalis is an understudied parasitic organism whose mechanisms of pathogenesis remain unclear. The adherence to host cells, the induction of host cell cytotoxicity and protease activity are all, however, thought to be contributing factors towards the development of the disease. T. vaginalis CP30 is an extracellular fraction containing four cysteine proteases, CP2, CP3, CP4 and CPT that induce apoptosis in primary human vaginal epithelial cells (HVECs) [Sommer U, Costello CE, Hayes GR, Beach DH, Gilbert RO, Lucas JJ, Singh BN. Identification of Trichomonas vaginalis cysteine proteases that induce apoptosis in human vaginal epithelial cells. J Biol Chem 2005; 280: 23853-60]. We now show that CP30, and the induction of HVEC apoptosis are modulated by iron availability in the parasite growth medium. Growth of parasites under high iron conditions results in a decrease in levels of CP30 found in an extracellular soluble fraction (SF), a concomitant decline in protease activity, and a decreased ability of SF to induce host cell death. Conversely, iron restriction leads to an increase in CP30 levels, an increase in CP30 protease activity, and an increased ability to induce HVEC cell death. Iron-loaded lactoferrin, but not transferrin is an effective iron source for parasites. We hypothesize that CP30 induction of host cell apoptosis is crucial for the development of a persistent infection, and that iron plays a determining role in parasite pathogenesis.