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Serum-sensitive mutation of Francisella novicida: association with an ABC transporter gene
K E Mdluli1, L S Anthony, G S Baron
1Department of Biochemistry and Microbiology, University of Victoria, Canada.
Abstract:
Francisella novicida is a facultative intracellular pathogen that can survive and grow in macrophages by preventing phagolysosomal fusion. In this study in vitro cassette mutagenesis was used to generate a library of insertion mutants of F.novicida. Two related mutants, KM14 and KM14S, initially identified as defective for growth in macrophages, were found to be sensitive to serum. These mutants were also found to grow approximately 1000-fold less well in the livers and spleens of infected mice. We cloned a genetic locus that was presumably mutagenized in these mutants and found that it included genes that had high similarity in their deduced amino acid sequence to those of msbA and orfE of Escherichia coli. The former is a member of the superfamily of ABC transporter proteins. We named the corresponding genes in F. novicida, valAB. Integration of a cloned valAB locus into the chromosome of KM14S partially restored the serum resistance phenotype found in wild-type F. novicida.
Insights
Francisella novicida mutants defective in macrophage growth were identified. These mutants showed serum sensitivity and reduced virulence in mice, linked to the novel valAB genes.
Area of Science:
- Microbiology
- Pathogen Biology
- Genetics
Background:
- Francisella novicida is a facultative intracellular pathogen.
- It survives in macrophages by inhibiting phagolysosomal fusion.
Purpose of the Study:
- To identify genes essential for Francisella novicida virulence.
- To characterize novel genetic loci involved in pathogen survival.
Main Methods:
- In vitro cassette mutagenesis to generate F. novicida mutants.
- Phenotypic analysis of mutants for serum sensitivity and intracellular growth.
- Cloning and characterization of a genetic locus (valAB) in F. novicida.
Main Results:
- Mutants KM14 and KM14S showed defects in macrophage growth, serum sensitivity, and reduced virulence in mice.
- A genetic locus, named valAB, was identified with homology to E. coli msbA and orfE.
- valAB genes encode putative ABC transporter proteins.
- Complementation with valAB partially restored serum resistance in mutant strains.
Conclusions:
- The valAB locus is crucial for Francisella novicida serum resistance and virulence.
- ABC transporter genes play a significant role in F. novicida pathogenesis.