Genome-Wide Transposon Mutagenesis in Pathogenic Leptospira Species

Abstract

Leptospira interrogans is the most common cause of leptospirosis in humans and animals. Genetic analysis of L. interrogans has been severely hindered by a lack of tools for genetic manipulation. Recently we developed the mariner-based transposon Himar1 to generate the first defined mutants in L. interrogans. In this study, a total of 929 independent transposon mutants were obtained and the location of insertion determined. Of these mutants, 721 were located in the protein coding regions of 551 different genes. While sequence analysis of transposon insertion sites indicated that transposition occurred in an essentially random fashion in the genome, 25 unique transposon mutants were found to exhibit insertions into genes encoding 16S or 23S rRNAs, suggesting these genes are insertional hot spots in the L. interrogans genome. In contrast, loci containing notionally essential genes involved in lipopolysaccharide and heme biosynthesis showed few transposon insertions. The effect of gene disruption on the virulence of a selected set of defined mutants was investigated using the hamster model of leptospirosis. Two attenuated mutants with disruptions in hypothetical genes were identified, thus validating the use of transposon mutagenesis for the identification of novel virulence factors in L. interrogans. This library provides a valuable resource for the study of gene function in L. interrogans. Combined with the genome sequences of L. interrogans, this provides an opportunity to investigate genes that contribute to pathogenesis and will provide a better understanding of the biology of L. interrogans.Leptospira interrogans is a spirochete that is the main causative agent of leptospirosis. This zoonosis has emerged as a major public health problem in much of the developing world, with more than 500,000 cases of severe leptospirosis reported each year, for which the mortality rate is more than 10% (17).The genus Leptospira is composed of both saprophytic and pathogenic species. The genome sequences of two epidemic strains of L. interrogans serovars Lai and Copenhageni have been determined (20,25). More recently a human and an animal L. borgpetersenii isolate were sequenced (3), and this year, we determined the genome sequence of the saprophyte L. biflexa (22). The resulting sequences provide an invaluable source of information for identification of genetic determinants involved in the pathogenicity and environmental biology of the organism. For example, the host-adapted L. borgpetersenii genome is 16% smaller and has many more pseudogenes than the L. interrogans genome. These findings suggest that genome reduction has resulted in a reduced environmental transmission potential (3). L. interrogans has 627 genes that are absent in the L. biflexa genome, and more than 500 of these genes have unknown functions, suggesting the presence of novel virulence mechanisms (22). However, the lack of tools for L. interrogans genetics has hindered elucidation of the role of these genes in pathogenesis.Pathogenic leptospires are difficult...

Use of Luminescent Leptospira interrogans for Enumeration in Biological Assays

“…1. Plasmid pAL612 contains transposon TnSC189 (2) and a ColE1 origin of replication from pBluescript II (13). Plasmid pAL615 was constructed by insertion of the flgB promoter from B. burgdorferi and the luxCDABE cassette from plasmid pSB406 (20).…”

“…Future work may use luminescent bacteria to image infections in live animals. Large numbers of mutants have now been generated in L. interrogans (13), and the lux reporter construct will be useful as a tool for the high-throughput investigation of mutant phenotypes in various in vitro assays. We thank Susan Thomas for technical assistance.…”

“…Transposon mutagenesis was conducted as described previously (1,13). In brief, the leptospires were grown to late log phase and made electrocompetent by repeated washing in ultrapure water.…”

“…This is currently the only efficient means for constructing defined leptospiral mutants. This method has been applied for widespread random mutagenesis of the bacterial chromosome (13), facilitating the identification of two virulence factors (14,17) and the unexpected finding that the major outer membrane protein (LipL32) is not required for pathogenesis (15).…”

Structural and Functional Characterization of an Orphan ATP-Binding Cassette ATPase Involved in Manganese Utilization and Tolerance in Leptospira spp

“…Indeed, targeted mutagenesis is extremely inefficient in pathogenic Leptospira (20). Our group has developed a system for random transposon mutagenesis using a mariner element, Himar1, in the saprophyte Leptospira biflexa (21) and the pathogen L. interrogans (22). This approach allowed the identification of specialized uptake systems for iron (21,23).…”