Identification of Chromosomal Genes in Yersinia pestis that Influence Type III Secretion and Delivery of Yops into Target Cells

Pathogenic Yersinia species possess a type III secretion system, which is required for the delivery of effector Yop proteins into target cells during infection. Genes encoding the type III secretion machinery, its substrates, and several regulatory proteins all reside on a 70-Kb virulence plasmid. Genes encoded in the chromosome of yersiniae are thought to play important roles in bacterial perception of host environments and in the coordinated activation of the type III secretion pathway. Here, we investigate the contribution of chromosomal genes to the complex regulatory process controlling type III secretion in Yersinia pestis. Using transposon mutagenesis, we identified five chromosomal genes required for expression or secretion of Yops in laboratory media. Four out of the five chromosomal mutants were defective to various extents at injecting Yops into tissue culture cells. Interestingly, we found one mutant that was not able to secrete in vitro but was fully competent for injecting Yops into host cells, suggesting independent mechanisms for activation of the secretion apparatus. When tested in a mouse model of plague disease, three mutants were avirulent, whereas two strains were severely attenuated. Together these results demonstrate the importance of Y. pestis chromosomal genes in the proper function of type III secretion and in the pathogenesis of plague

Effects of detuning and dispersion on the dynamics of FM mode-locked Ti:sapphire laser

A theoretical modeling of the dynamics of mode locking taking into account the effects of dispersion and detuning applied to the study of pulse evolution inside the FM mode locked Ti:sapphire laser is presented. We note that a considerable change in the pulsewidth and pulse evolution time is brought about by dispersion and detuning. Typically pulsewidths of around ten's of picoseconds is conceivable in systems where dispersion and detuning are well within desired values. The pulse evolution time varies depending on the values of the dispersion and detuning and is typically found to be around 200 μse