Comparative Transcriptional Analyses of Francisella tularensis and Francisella novicida

Siva T Sarva,Robert J Belland,Robert H Waldo,Karl E Klose,Chandra Shekhar Bakshi

doi:10.1371/journal.pone.0158631

Siva T Sarva, Robert J Belland + Show 3 more

Open Access

https://doi.org/10.1371/journal.pone.0158631

Copy DOI

Abstract

Francisella tularensis is composed of a number of subspecies with varied geographic distribution, host ranges, and virulence. In view of these marked differences, comparative functional genomics may elucidate some of the molecular mechanism(s) behind these differences. In this study a shared probe microarray was designed that could be used to compare the transcriptomes of Francisella tularensis subsp. tularensis Schu S4 (Ftt), Francisella tularensis subsp. holarctica OR960246 (Fth), Francisella tularensis subsp. holarctica LVS (LVS), and Francisella novicida U112 (Fn). To gain insight into expression differences that may be related to the differences in virulence of these subspecies, transcriptomes were measured from each strain grown in vitro under identical conditions, utilizing a shared probe microarray. The human avirulent Fn strain exhibited high levels of transcription of genes involved in general metabolism, which are pseudogenes in the human virulent Ftt and Fth strains, consistent with the process of genome decay in the virulent strains. Genes encoding an efflux system (emrA2 cluster of genes), siderophore (fsl operon), acid phosphatase, LPS synthesis, polyamine synthesis, and citrulline ureidase were all highly expressed in Ftt when compared to Fn, suggesting that some of these may contribute to the relative high virulence of Ftt. Genes expressed at a higher level in Ftt when compared to the relatively less virulent Fth included genes encoding isochorismatases, cholylglycine hydrolase, polyamine synthesis, citrulline ureidase, Type IV pilus subunit, and the Francisella Pathogenicity Island protein PdpD. Fth and LVS had very few expression differences, consistent with the derivation of LVS from Fth. This study demonstrated that a shared probe microarray designed to detect transcripts in multiple species/subspecies of Francisella enabled comparative transcriptional analyses that may highlight critical differences that underlie the relative pathogenesis of these strains for humans. This strategy could be extended to other closely-related bacterial species for inter-strain and inter-species analyses.

Highlights

Francisella tularensis is a highly virulent Gram negative bacterium
The disease caused by F. tularensis, can present with different clinical symptoms depending on the route of entry into the human host
Our goal was to create a single microarray for these species/subspecies that would enable comparative expression studies between Ftt, Francisella tularensis subsp. holarctica OR960246 (Fth), and/or Francisella novicida U112 (Fn)

Summary

Introduction

Francisella tularensis is a highly virulent Gram negative bacterium. A pulmonary exposure to as few as 20 bacteria is believed to cause a fatal human disease [1]. The disease caused by F. tularensis, can present with different clinical symptoms depending on the route of entry into the human host. Ulcero-glandular tularemia is responsible for most of the natural cases of F. tularensis infection, but other clinical forms include occulo-glandular, gastrointestinal, and pulmonary tularemia. All forms can progress to a systemic infection that includes severe prostration, multi-system organ failure, and in some cases death. The threat of bioterrorism has sparked resurgence in research on this pathogen, in order to develop novel therapies and effective vaccine strategies [2, 3]

Objectives

Methods

Results

Conclusion