Characterization of regulatory pathways in Xylella fastidiosa: genes and phenotypes controlled by algU.
ABSTRACT Many virulence genes in plant bacterial pathogens are coordinately regulated by "global" regulatory genes. Conducting DNA microarray analysis of bacterial mutants of such genes, compared with the wild type, can help to refine the list of genes that may contribute to virulence in bacterial pathogens. The regulatory gene algU, with roles in stress response and regulation of the biosynthesis of the exopolysaccharide alginate in Pseudomonas aeruginosa and many other bacteria, has been extensively studied. The role of algU in Xylella fastidiosa, the cause of Pierce's disease of grapevines, was analyzed by mutation and whole-genome microarray analysis to define its involvement in aggregation, biofilm formation, and virulence. In this study, an algU::nptII mutant had reduced cell-cell aggregation, attachment, and biofilm formation and lower virulence in grapevines. Microarray analysis showed that 42 genes had significantly lower expression in the algU::nptII mutant than in the wild type. Among these are several genes that could contribute to cell aggregation and biofilm formation, as well as other physiological processes such as virulence, competition, and survival.
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ABSTRACT: Xylella fastidiosa is responsible for several economically important plant diseases. It is currently assumed that the symptoms are caused by vascular occlusion due to biofilm formation. Microarray technology was previously used to examine the global gene expression profile of X. fastidiosa freshly isolated from symptomatic plants or after several passages by axenic culture medium, and different pathogenicity profiles have been obtained. In the present study the expression of some pathogenicity-related genes was evaluated in vitro and in planta by RT-PCR. The results suggest that adhesion is important at the beginning of biofilm formation, while the genes related to adaptation are essential for the organism's maintenance in planta. Similar results were observed in vitro mainly for the adhesion genes. The pattern of expression observed suggests that adhesion modulates biofilm formation whereas the expression of some adaptation genes may be related to the environment in which the organism is living.Current Microbiology 05/2005; 50(4):223-8. · 1.82 Impact Factor
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ABSTRACT: Global transcription responses of Escherichia coli to various stimuli or genetic defects were studied by measuring mRNA levels in about 400 segments of the genome. Measuring mRNA levels was done by analyzing hybridization to DNA dot blots made with overlapping lambda clones spanning the genome of E. coli K-12. Conditions examined included isopropyl-beta-D-thiogalactopyranoside (IPTG) induction, heat shock, osmotic shock, starvation for various nutrients, entrance of cells into the stationary phase of growth, anaerobic growth in a tube, growth in the gnotobiotic mouse gut, and effects of pleiotropic mutations rpoH, himA, topA, and crp. Most mapped genes known to be regulated by a particular situation were successfully detected. In addition, many chromosomal regions containing no previously known regulated genes were discovered that responded to various stimuli. This new method for studying globally regulated genetic systems in E. coli combines detection, cloning, and physical mapping of a battery of coregulated genes in one step.Journal of Bacteriology 05/1993; 175(7):2026-36. · 3.83 Impact Factor
Article: Alginate gene expression by Pseudomonas syringae pv. tomato DC3000 in host and non-host plants.[show abstract] [hide abstract]
ABSTRACT: Pseudomonas syringae produces the exopolysaccharide alginate, a copolymer of mannuronic and guluronic acid. Although alginate has been isolated from plants infected by P. syringae, the signals and timing of alginate gene expression in planta have not been described. In this study, an algD : : uidA transcriptional fusion, designated pDCalgDP, was constructed and used to monitor alginate gene expression in host and non-host plants inoculated with P. syringae pv. tomato DC3000. When leaves of susceptible collard plants were spray-inoculated with DC3000(pDCalgDP), algD was activated within 72 h post-inoculation (p.i.) and was associated with the development of water-soaked lesions. In leaves of the susceptible tomato cv. Rio Grande-PtoS, algD activity was lower than in collard and was not associated with water-soaking. The expression of algD was also monitored in leaves of tomato cv. Rio Grande-PtoR, which is resistant to P. syringae pv. tomato DC3000. Within 12 h p.i., a microscopic hypersensitive response (micro-HR) was observed in Rio Grande-PtoR leaves spray-inoculated with P. syringae pv. tomato DC3000(pDCalgDP). As the HR progressed, histochemical staining indicated that individual bacterial cells on the surface of resistant tomato leaves were expressing algD. These results indicate that algD is expressed in both susceptible (e.g. collard, tomato) and resistant (Rio Grande-PtoR) host plants. The expression of algD in an incompatible host-pathogen interaction was further explored by monitoring transcriptional activity in leaves of tobacco, which is not a host for P. syringae pv. tomato. In tobacco inoculated with DC3000(pDCalgDP), an HR was evident within 12 h p.i., and algD expression was evident within 8-12 h p.i. However, when tobacco was inoculated with an hrcC mutant of DC3000, the HR did not occur and algD expression was substantially lower. These results suggest that signals that precede the HR may stimulate alginate gene expression in P. syringae. Histochemical staining with nitro blue tetrazolium indicated that the superoxide anion () is a signal for algD activation in planta. This study indicates that algD is expressed when P. syringae attempts to colonize both susceptible and resistant plant hosts.Microbiology 06/2003; 149(Pt 5):1127-38. · 3.06 Impact Factor