The plant pathogen Pseudomonas fuscovaginae contains two conserved quorum sensing systems involved in virulence and negatively regulated by RsaL and the novel regulator RsaM.

Pseudomonas fuscovaginae is a Gram-negative fluorescent pseudomonad pathogenic towards several plant species. Despite its importance as a plant pathogen, no molecular studies of virulence have thus far been reported. In this study we show that P. fuscovaginae possesses two conserved N-acyl homoserine lactone (AHL) quorum sensing (QS) systems which we designated PfsI/R and PfvI/R. The PfsI/R system is homologous to the BviI/R system of Burkholderia vietnamiensis and produces and responds to C10-HSL and C12-HSL whereas PfvI/R is homologous to the LasI/R system of Pseudomonas aeruginosa and produces several long-chain 3-oxo-HSLs and responds to 3-oxo-C10-HSL and 3-oxo-C12-HSL and at high AHL concentrations can also respond to structurally different long-chain AHLs. Both systems were found to be negatively regulated by a repressor protein which was encoded by a gene located intergenically between the AHL synthase and LuxR-family response regulator. The pfsI/R system was regulated by a novel repressor designated RsaM while the pfvI/R system was regulated by both the RsaL repressor and by RsaM. The two systems are not transcriptionally hierarchically organized but share a common AHL response and both are required for plant virulence. Pseudomonas fuscovaginae has therefore a unique complex regulatory network composed of at least two different repressors which directly regulate the AHL QS systems and pathogenicity.

Confirmation of the value of a modified long-distance polymerase chain reaction in the detection of inversion intron 22 in severe hemophilia a: a technical note.

Hemophilia A is one of the most common bleeding disorders in man. Approximately half the families with a severe disease have an inversion of the factor VIII gene. The inversion may be detected with a long polymerase chain reaction. This is a simple and reproducible method that may yield satisfactory results in approximately 24 hours. The long-distance polymerase chain reaction amplify three very large amplicons with a very GC-rich region of several kilobases, and is detected with a Expand Long Template DNA polymerase (Roche, Mannheim, Germany). Recently this polymerase has been changed with a new chemical composition. The object of the present method is to standardize the technique using the new Expand Long polymerase. For the new protocol, the cycling conditions, the concentration of nucleotide primers, and the buffer are changed. The need for a rapid response is determined in the case of hemophilia A patients, not only by the desire to reach a proper classification, but also by the urgency to inform the carrier status of the mother or of a female relative.

Severe prekallikrein (Fletcher factor) deficiency due to a compound heterozygosis (383Trp stop codon and Cys529Tyr).

We investigated a family with prekallikrein deficiency, using both standard coagulation tests and molecular biology techniques. The propositus was found to be a compound heterozygote for a Trp383 stop codon and a Cys529Tyr point mutation. The former mutation was located in exon 11, the latter in exon 14. The propositus inherited the first defect from his father and the second from his mother. Both parents had slightly low prekallikrein levels, but the combination of the two genetic defects produced a phenotype characterized by an extremely low prekallikrein activity and antigen. The propositus' plasma showed a progressive reduction in APTT when incubated for a long time. Conversely, plasma deficient in factor XII, factor XI or high molecular weight kininogen (HMWK) failed to show shortening of the APTT. No circulating anticoagulant was found because the patient's APTT was fully corrected by pooled nor-mal and factor XII-, factor XI- or HMWK deficient plasma. No associated abnormality was apparent in the propositus or his parents. As expected, no tendency for bleeding was noted even after tonsillectomy.

Conformation sensitive gel electrophoresis for detection of factor X gene mutations.

Fifteen patients from five families with laboratory data suggesting factor X (FX) deficiency were screened for causative mutations by conformation sensitive gel electrophoresis (CSGE) followed by sequencing. All exonic and flanking intronic regions of factor X gene were amplified using PCR. After heteroduplex formation, samples were analyzed onto a polyacrylamide gel for possible mismatch. An abnormal CSGE profile indicating an heteroduplex was identified in 10/15 cases. All the 10 patients with a patter of migration suggesting a mismatch had a laboratoristic pattern of FX deficiency whereas the five cases with a normal CSGE aspect referred to the normal components of the families who did not carry any FX defect. Sequencing demonstrated that the 10 exons, which showed a suspect CSGE pattern, harbored a mutation responsible for the factor X defect. Of the five mutation identified, two were recognized to be novel mutations (a 871C>T substitution and a 1169G>T transversion in exon 8), both located in the catalytic portion of FX. CSGE may be an effective and simple procedure for screening factor X gene mutations.

A new mutation (Arg251Trp) in the Ca2+ binding site of factor X protease domain appears to be responsible for the defect in the extrinsic pathway activation of factor X Padua.

Factor X Padua, first described a few years ago, is characterized by a defect only in the extrinsic system. In this present paper, the molecular basis for this peculiar defect is investigated. Polymerase chain reaction amplification and direct sequencing of the entire FX coding sequence and of exon-intron junctions detected in the proposita a C-to-T translocation in exon 8 of nucleotide 875 at the homozygous level. This resulted in the substitution of tryptophan for arginine 251. A niece of the proposita was shown to be heterozygous for the abnormality. Molecular modeling suggested that the mutation does not alter significantly folding and stability of the protein but may be involved in the Ca2+ binding site.

A large deletion due to a new mutation (intron 13/exon 23) in a sporadic case of severe hemophilia A.

A case of sporadic hemophilia A in a young child was investigated from a molecular biology point of view. The propositus is a 4-year-old severe hemophiliac who was first seen when he was 2 years old. At that time, easy bruising and hematomas were noted because of accidental falls while toddling. The coagulation study showed a prolonged partial thromboplastin time and a factor VIII level of 1.3% of normal. Molecular biologic analysis showed a large deletion involving intron 13 up to exon 23. In the inversion study, the propositus exhibited only a 10 kb band, and this result suggests that intron 22 was deleted while his mother shows a normal pattern. To further examine the length of the deletion, a long polymerase chain reaction by means of primers amplifying the region from exon 13 to 23. In the index patient, an approximate 13-kb product was obtained, whereas no product was obtained from his mother. The mother investigated by means of polymorphism was shown not to be a carrier.

Involvement of a quorum-sensing-regulated lipase secreted by a clinical isolate of Burkholderia glumae in severe disease symptoms in rice.

Burkholderia glumae is an emerging rice pathogen in several areas around the world. Closely related Burkholderia species are important opportunistic human pathogens for specific groups of patients, such as patients with cystic fibrosis and patients with chronic granulomatous disease. Here we report that the first clinical isolate of B. glumae, strain AU6208, has retained its capability to be very pathogenic to rice. As previously reported for rice isolate B. glumae BGR1 (and also for the clinical isolate AU6208), TofI or TofR acyl homoserine lactone (AHL) quorum sensing played a pivotal role in rice virulence. We report that AHL quorum sensing in B. glumae AU6208 regulates secreted LipA lipase and toxoflavin, the phytotoxin produced by B. glumae. B. glumae AU6208 lipA mutants were no longer pathogenic to rice, indicating that the lipase is an important virulence factor. It was also established that type strain B. glumae ATCC 33617 did not produce toxoflavin and lipase and was nonpathogenic to rice. It was determined that in strain ATCC 33617 the LuxR family quorum-sensing sensor/regulator TofR was inactive. Introducing the tofR gene of B. glumae AU6208 in strain ATCC 33617 restored its ability to produce toxoflavin and the LipA lipase. This study extends the role of AHL quorum sensing in rice pathogenicity through the regulation of a lipase which was demonstrated to be a virulence factor. It is the first report of a clinical B. glumae isolate retaining strong rice pathogenicity and finally determined that B. glumae can undergo phenotypic conversion through a spontaneous mutation in the tofR regulator.