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Clustering of mutations affecting alginic acid biosynthesis in mucoid Pseudomonas aeruginosa
Abstract:
A 10-kilobase DNA fragment previously shown to contain the phosphomannose isomerase gene (pmi) of Pseudomonas aeruginosa was used to construct a pBR325-based hybrid that can be propagated in P. aeruginosa only by the formation of a chromosomal-plasmid cointegrate. This plasmid, designated pAD4008, was inserted into the P. aeruginosa chromosome by recombination at a site of homology between the cloned P. aeruginosa DNA and the chromosome. Mobilization of pAD4008 into P. aeruginosa PAO and 8830 and selection for the stable acquisition of tetracycline resistance resulted in specific and predictable changes in the pattern of endonuclease restriction sites in the phosphomannose isomerase gene region of the chromosomes. Chromosomal DNA from the tetracycline-resistant transformants was used to clone the drug resistance determinant with Bg/II or XbaI, thereby allowing the "walking" of the P. aeruginosa chromosome in the vicinity of the pmi gene. Analysis of overlapping tetracycline-resistant clones indicated the presence of sequences homologous to the DNA insert of plasmid pAD2, a recombinant clone of P. aeruginosa origin previously shown to complement several alginate-negative mutants. Restriction mapping, subcloning, and complementation analysis of a 30-kilobase DNA region demonstrated the tight clustering of several genetic loci involved in alginate biosynthesis. Furthermore, the tetracycline resistance determinant in PAO strain transformed by pAD4008 was mapped on the chromosome by plasmid FP2-mediated conjugation and was found to be located near 45 min.
Insights
Researchers used a novel plasmid to map genes involved in Pseudomonas aeruginosa alginate biosynthesis. This method allowed for the "walking" of the bacterial chromosome, revealing a clustered arrangement of alginate biosynthesis genes near the phosphomannose isomerase gene.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Pseudomonas aeruginosa is an opportunistic pathogen known for its ability to produce alginate, a key virulence factor.
- Understanding the genetic regulation of alginate biosynthesis is crucial for developing targeted therapeutic strategies.
- Previous studies identified the phosphomannose isomerase (pmi) gene as a component of this pathway.
Purpose of the Study:
- To develop a method for cloning and characterizing genes involved in Pseudomonas aeruginosa alginate biosynthesis.
- To map the genetic loci responsible for alginate production in the P. aeruginosa chromosome.
- To investigate the organization and clustering of alginate biosynthesis genes.
Main Methods:
- Construction of a pBR325-based hybrid plasmid (pAD4008) containing a 10-kilobase DNA fragment with the P. aeruginosa phosphomannose isomerase (pmi) gene.
- Integration of pAD4008 into the P. aeruginosa chromosome via homologous recombination, creating cointegrates.
- Selection for tetracycline resistance in transformed P. aeruginosa strains to identify successful integration events.
- Utilizing Bg/II or XbaI restriction enzymes to clone the tetracycline resistance determinant and perform chromosomal walking.
- Restriction mapping, subcloning, and complementation analysis of a 30-kilobase DNA region.
Main Results:
- Successful integration of pAD4008 into the P. aeruginosa chromosome, leading to predictable changes in restriction patterns around the pmi gene.
- Identification of overlapping clones demonstrating homology to previously characterized alginate biosynthesis genes (plasmid pAD2 insert).
- Demonstration of a tight cluster of several genetic loci involved in alginate biosynthesis within a 30-kilobase region.
- Mapping of the tetracycline resistance determinant to approximately 45 minutes on the P. aeruginosa chromosome using plasmid FP2-mediated conjugation.
Conclusions:
- The developed cointegrate plasmid system is effective for targeted gene cloning and chromosomal walking in P. aeruginosa.
- Alginate biosynthesis genes in P. aeruginosa are tightly clustered on the chromosome, suggesting coordinated regulation.
- This study provides a foundation for further elucidation of the complex genetic pathways governing alginate production in P. aeruginosa.