The Fitness Landscape of the African Salmonella Typhimurium ST313 Strain D23580 Reveals Unique Properties of the pBT1 Plasmid

Authors

Rocío Canals, University of Liverpool
Roy R. Chaudhuri, University of Sheffield
Rebecca E. Steiner, The Ohio State University
Siân V. Owen, University of Liverpool
Natalia Quinones-Olvera, Harvard University
Melita A. Gordon, University of Liverpool
Michael Baym, University of Liverpool
Michael Ibba, Chapman UniversityFollow
Jay C. D. Hinton, University of Liverpool

Document Type

Article

Publication Date

9-27-2019

Abstract

We have used a transposon insertion sequencing (TIS) approach to establish the fitness landscape of the African Salmonella enterica serovar Typhimurium ST313 strain D23580, to complement our previous comparative genomic and functional transcriptomic studies. We used a genome-wide transposon library with insertions every 10 nucleotides to identify genes required for survival and growth in vitro and during infection of murine macrophages. The analysis revealed genomic regions important for fitness under two in vitro growth conditions. Overall, 724 coding genes were required for optimal growth in LB medium, and 851 coding genes were required for growth in SPI-2-inducing minimal medium. These findings were consistent with the essentiality analyses of other S. Typhimurium ST19 and S. Typhi strains. The global mutagenesis approach also identified 60 sRNAs and 413 intergenic regions required for growth in at least one in vitro growth condition. By infecting murine macrophages with the transposon library, we identified 68 genes that were required for intra-macrophage replication but did not impact fitness in vitro. None of these genes were unique to S. Typhimurium D23580, consistent with a high conservation of gene function between S. Typhimurium ST313 and ST19 and suggesting that novel virulence factors are not involved in the interaction of strain D23580 with murine macrophages. We discovered that transposon insertions rarely occurred in many pBT1 plasmid-encoded genes (36), compared with genes carried by the pSLT-BT virulence plasmid and other bacterial plasmids. The key essential protein encoded by pBT1 is a cysteinyl-tRNA synthetase, and our enzymological analysis revealed that the plasmid-encoded CysRS^pBT1 had a lower ability to charge tRNA than the chromosomally-encoded CysRS^chr enzyme. The presence of aminoacyl-tRNA synthetases in plasmids from a range of Gram-negative and Gram-positive bacteria suggests that plasmid-encoded essential genes are more common than had been appreciated.

Comments

This article was originally published in PLoS Pathogens, volume 15, in 2019. https://doi.org/10.1371/journal.ppat.1007948

Recommended Citation

Canals, R., Chaudhuri, R.R., Steiner, R.E., Owen, S.V., Quinones-Olvera, N., Gordon, M.A., Ibba, M. and Hinton, J.C.D. (2019) The fitness landscape of the African Salmonella Typhimurium ST313 strain D23580 reveals unique properties of the pBT1 plasmid. PLoS Path. 15:e1007948. https://doi.org/10.1371/journal.ppat.1007948

Copyright

The authors

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This work is licensed under a Creative Commons Attribution 4.0 License.