A small RNA regulation of virulence in Lyme disease pathogen

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Project Summary/Abstract Lyme disease, a prevalent arthropod-borne disease, is caused by the bacterial pathogen Borrelia burgdorferi. The microbes live in an intricate enzootic life cycle involving both Ixodes ticks and diverse mammalian species. To survive in its complex cycle and navigate through disparate sets of tissue environments, such as ones in mammalian hosts or in ticks, B. burgdorferi must regulate gene expression in a tight temporal and spatial manner, although the mechanism of such gene regulation remains unclear. Posttranscriptional gene regulation via a variety of small regulatory RNAs (sRNAs) is one mechanism of modulating gene expression in bacteria. Base pairing between the sRNAs and target mRNAs can trigger alterations in mRNA translation and stability, thereby influencing target gene expression. The small RNAs also bind to proteins, either sequestering or affecting the activities of proteins. Previous studies have reported that a small RNA, DsrABb, regulates RpoS gene expression in B. burgdorferi. Moreover, recent studies identified over 1000 B. burgdorferi sRNAs that are differentially regulated by environmental conditions, suggesting that sRNAs may play a role in gene regulation for spirochete adaptation during its enzootic cycle, although their precise functions or importance in spirochete biology and infectivity remain largely enigmatic. Most recently, an intergenic non-coding small RNA located upstream of bbd18, called ittA, was characterized and shown to be required for optimal infectivity and tissue tropism in B. burgdorferi. In fact, the intergenic region of bbd17 and bbd18 was reported to harbor a small RNA 0735 (SR0735), that is highly expressed at 37°C (mammalian host body temperature). Our preliminary data showed that the insertion of a kanamycin cassette upstream of SR0735 affects B. burgdorferi infectivity and decreases the level of SR0735, as shown in Northern blot and RT-PCR analyses, suggesting a critical importance of SR0735 in microbial virulence. The goals of our current proposal are to study the potential role of this sRNA in spirochete biology and virulence, and to identify its potential target RNA and/or protein binding partners. This study will uncover the sRNA regulatory mechanisms in spirochete biology and may help to decipher the functions of sRNAs in spirochete virulence and pathogenesis.