SERUM-SENSITIVE MUTATION OF FRANCISELLA-NOVICIDA - ASSOCIATION WITH AN ABC TRANSPORTER GENE

Francisella novicida is a facultative intracellular pathogen that can survive and grow in macrophages by preventing phagolysosomal fusion. I n this study in vitro cassette mutagenesis was used to generate a libr ary of insertion mutants of F. novicida. Two related mutants, KM14 and KM14S, initially identified as defective for growth in macrophages, w ere found to be sensitive to serum. These mutants were also found to g row approximately 1000-fold less well in the livers and spleens of inf ected mice. We cloned a genetic locus that was presumably mutagenized in these mutants and found that it included genes that had high simila rity in their deduced amino acid sequence to those of msbA and orFE of Escherichia coil. The former is a member of the superfamily of ABC tr ansporter proteins. We named the corresponding genes in F. novicida, v alAB. Integration of a cloned valAB locus into the chromosome of KM14S partially restored the serum resistance phenotype found in wild-type F. novicida.