The Two-Component System DcuS-DcuR Is Involved in Virulence and Stress Tolerance in the Poplar Canker Bacterium Lonsdalea populi

The gram-negative bacterium Lonsdalea populi causes an emerging poplar (Populus × euramericana) canker resulting in severe losses to poplar production in China and Europe. Two-component signal transduction systems play important roles in the regulation of virulence and stress responses in phytopathogenic bacteria. We identified a two-component pair (Lqp2625-Lqp2624) in L. populi, highly homologous to DcuS-DcuR of Escherichia coli. Mutants lacking DcuS or DcuR displayed normal growth while their virulence on poplar twigs was impaired. An inability to produce flagella indicated that DcuS and DcuR are involved in biofilm formation and swimming motility. Moreover, the loss of DcuS or DcuR led to increased sensitivity to oxidative stress and chloramphenicol through downregulation of genes associated with catalases and the multidrug efflux pump, suggesting that the two-component pair contributes to cellular adaptation to oxidative and antibiotic stresses. We identified key domains and putative phosphorylation sites important for virulence and stress responses. Our findings reveal the functions of DcuS-DcuR in virulence and stress responses in L. populi and provide increasing evidence that two-component systems are crucial during the infection process and stress adaptation in bacteria.

Geometry of emission in PSR 1929+10

Rankin (1990) attempted to distinguish between one- and two-pole interpulse models for PSR 1929+10, and, despite the evidence to the contrary (Lyne & Manchester 1988; Phillips 1990), argued that it was probably a two-pole interpulsar on the basis of its narrow components.Ifit is a two-pole interpulsar, its interpulse has just the right width to be a core component—that is,, the angular width of the polar cap. However, PSR 1929+10 was virtually the only well studied pulsar of any profile class which could not be comfortably fitted into the quantitative description of the conal emission geometry as discussed by Rankin (1993 a,b). The problem arose due to the narrow dimensions of the conal component pair in this pulsar, which do not fit well with the inner and outer cone properties followed by many pulsars. In order to explore this issue further, we use the technique of constructing partial ‘mode-separated’ profiles corresponding to the primary and secondary polarisation modes.