The Borreliella burgdorferi BosR-associated small non-coding RNA BasA regulates virulence.

Post-transcriptional regulation is an adaptive response used by living systems to alter protein levels independently of transcription initiation. In bacteria, one mechanism of post-transcriptional regulation involves the binding of small, non-coding RNAs (sRNAs) to target mRNAs to regulate their translation into protein. This regulation generally includes an RNA-binding protein that facilitates the sRNA::mRNA interaction. In the etiological agent of Lyme disease, Borreliella burgdorferi, over 400 temperature-dependent sRNAs have been identified. Here, we characterized the sRNA SR0735, which is upregulated at 37°C (characteristic of mammalian infection). Transcriptomic and proteomic analyses revealed that deleting SR0735 in B. burgdorferi resulted in reduced production of virulence-associated, RpoS-dependent proteins due to a reduction of RpoS and its upstream regulator BosR. We thus renamed SR0735 as BasA for BosR-associated sRNA locus A. Consistent with previous studies that identified BosR as an RNA-binding protein, we demonstrate here that BosR can bind BasA in vitro. Importantly, the loss of BasA significantly attenuated B. burgdorferi infectivity during murine infection, which is consistent with the reduced levels of BosR and RpoS observed. The emerging model suggests that BasA is required for optimal levels of BosR protein through the post-transcriptional regulation of bosR mRNA, which, in turn, promotes the production of RpoS and its downstream genes required for mammalian infectivity and pathogenesis.