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Reciprocal Regulation of Bioluminescence and Type III Protein Secretion in Vibrio harveyi and Vibrio parahaemolyticus in Response to Diffusible Chemical Signals. Stephen C. Winans, 2004. OXA-60, a Chromosomal, Inducible, and Imipenem-Hydrolyzing Class D ß-Lactamase from Ralstonia pickettii. Delphine Girlich, 2004.A chromosomally encoded oxacillinase, OXA-22, had been characterized from Ralstonia pickettii PIC-1 that did not explain by itself the resistance profile of this strain to ß-lactams . Thus, further analysis of the genetic background of this species led to the identification of another oxacillinase, OXA-60, that was expressed only after ß-lactam induction . This chromosomally encoded oxacillinase shared 19% amino acid identity with OXA-22 . It has a narrow-spectrum hydrolysis profile that includes imipenem . OXA-60-like enzymes were identified in several R . pickettii strains . Gene inactivation and induction studies of the blaOXA-60 and blaOXA-22 genes in R . pickettii identified the relative contribution of each oxacillinase to the resistance profile of R . pickettii to ß-lactams . Spiralin Is Not Essential for Helicity, Motility, or Pathogenicity but Is Required for Efficient Transmission of Spiroplasma citri by Its Leafhopper Vector Circulifer haematoceps. Sybille Duret, 2003.Spiralin is the most abundant protein at the surface of the plant pathogenic mollicute Spiroplasma citri and hence might play a role in the interactions of the spiroplasma with its host plant and/or its insect vector . To study spiralin function, mutants were produced by inactivating the spiralin gene through homologous recombination . A spiralin-green fluorescent protein (GFP) translational fusion was engineered and introduced into S . citri by using an oriC-based targeting vector . According to the strategy used, integration of the plasmid by a single-crossover recombination at the spiralin gene resulted in the expression of the spiralin-GFP fusion protein . Two distinct mutants were isolated . Western and colony immunoblot analyses showed that one mutant (GII3-9a5) did produce the spiralin-GFP fusion protein, which was found not to fluoresce, whereas the other (GII3-9a2) produced neither the fusion protein nor the wild-type spiralin . Both mutants displayed helical morphology and motility, similarly to the wild-type strain GII-3 . Genomic DNA analyses revealed that GII3-9a5 was unstable and that GII3-9a2 was probably derived from GII3-9a5 by a double-crossover recombination between plasmid sequences integrated into the GII3-9a5 chromosome and free plasmid . When injected into the leafhopper vector Circulifer haematoceps, the spiralinless mutant GII3-9a2 multiplied to high titers in the insects (1.1 x 106 to 2.8 x 106 CFU/insect) but was transmitted to the host plant 100 times less efficiently than the wild-type strain . As a result, not all plants were infected, and symptom production in these plants was delayed for 2 to 4 weeks compared to that in the wild-type strain . In the infected plants however, the mutant multiplied to high titers (1.2 x 106 to 1.4 x 107 CFU/g of midribs) and produced the typical symptoms of the disease . These results indicate that spiralin is not essential for pathogenicity but is required for efficient transmission of S . citri by its insect vector .
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