Identification and characterization of small RNAs expressed by Leptospira borgpetersenii serovar Hardjo and their conservation in the genus Leptospira

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BACKGROUND: Leptospirosis is a global zoonotic disease affecting humans, companion animals, and domestic livestock. Clinical presentation of disease is dependent on complex interactions between host species and pathogenic species, serovars, and strains of Leptospira. This is exemplified by L. borgpetersenii serovar Hardjo strains HB203 and JB197, which differ very little by genome content but cause divergent clinical disease phenotypes in the hamster model of leptospirosis. JB197 causes an acute lethal disease while HB203 establishes a chronic asymptomatic infection of the kidneys. Previous work has shown that Leptospira modify their gene expression in response to temperature. RESULTS: RNA sequencing performed on serovar Hardjo strains HB203 and JB197 cultured at both 29˚C and 37˚C directly from experimentally infected hamsters identified 266 small RNAs (sRNAs) previously unannotated for L. borgpetersenii. Levels of expression for each novel candidate sRNA are reported: 67 and 10 sRNAs were differentially expressed between strains (at 29˚C and 37˚C respectively) while 32 and 10 were differentially expressed between temperature conditions (within JB197 and HB203 respectively). Conservation analysis of candidate sRNAs within the genus Leptospira identified a binomial distribution comprising highly conserved sRNAs such as JB_C1_N135/LIC1nc80 and JB_C1_N610 which are found in 42/43 pathogenic species compared to others such as JB_C1_N595 and JB_C1_N1040 which are restricted to strains of L. borgpetersenii. CONCLUSIONS: The nuances of what contributes to Leptospira strain-specific pathogenesis are poorly understood. Non-coding sRNAs have regulatory impacts on gene expression that can alter leptospire protein profiles, virulence factors, and host-pathogen interactions. Levels of conservation of these sRNAs within the genus Leptospira identified those that were highly conserved compared to others that were species-specific. Results emphasize the broad role that sRNAs play in regulating gene expression of Leptospira, and the potential for sRNAs to be used for clinical detection as well as species/serovar specific typing.

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