Abstract
The F. tularensis type A strain FSC198 from Slovakia and a second strain FSC043, which has attenuated virulence, are both considered to be derivatives of the North American F. tularensis type A strain SCHU S4. These strains have been propagated under different conditions: the FSC198 has undergone natural propagation in the environment, while the strain FSC043 has been cultivated on artificial media in laboratories. Here, we have compared the genome sequences of FSC198, FSC043, and SCHU S4 to explore the possibility that the contrasting propagation conditions may have resulted in different mutational patterns. We found four insertion/deletion events (INDELs) in the strain FSC043, as compared to the SCHU S4, while no single nucleotide polymorphisms (SNPs) or variable number of tandem repeats (VNTRs) were identified. This result contrasts with previously reported findings for the strain FSC198, where eight SNPs and three VNTR differences, but no INDELs exist as compared to the SCHU S4 strain. The mutations detected in the laboratory and naturally propagated type A strains, respectively, demonstrate distinct patterns supporting that analysis of mutational spectra might be a useful tool to reveal differences in past growth conditions. Such information may be useful to identify leads in a microbial forensic investigation.
Highlights
Following the anthrax attacks of 2001, microbial forensics has emerged as a new scientific discipline dedicated to the investigation of biocrime and bioterrorism to link pathogen, crime, and perpetrator [1]
Identified mutational patterns Direct mapping of sequence reads from FSC043 on the genome sequences of FSC198 and SCHU S4 showed an average coverage of 1076separated by highly repetitive regions
Genome-wide sequence comparisons between strain FSC043 and strain SCHU S4 did not identify any single nucleotide polymorphisms (SNPs) between the two strains and they showed identical variable number of tandem repeats (VNTRs) patterns, while three VNTRs differentiated them from FSC198
Summary
Following the anthrax attacks of 2001, microbial forensics has emerged as a new scientific discipline dedicated to the investigation of biocrime and bioterrorism to link pathogen, crime, and perpetrator [1]. Nonneutral mutations may provide a different but potentially important aspect for microbial forensics. Since such mutations may reflect the selective forces experienced by a bacterium, they may provide information on past propagation conditions. We investigate this possibility by comparing mutational patterns detected in three strains designated SCHU S4 (FSC237), FSC198 (SE-219), and FSC043 of Francisella tularensis subspecies tularensis (type A1). Type A strains (in particular subgroup A1) demonstrate high virulence to humans [4] compared to the two other subspecies holarctica (type B) and mediasiatica, and are almost entirely restricted to North America [5]. Data from the study provided plausible evidence supporting that the European isolates represent valid natural isolates and not events of laboratory contamination
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